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  • 151.
    Kellner, Hans
    et al.
    Högskolan Dalarna, Akademin Industri och samhälle, Materialteknik. KTH.
    Karasev, A. V.
    Sundqvist, O.
    Jönsson, P. G.
    Effect of the Stirring Mode on the Behavior of Al2O3–MgO Particles and Clusters during Ladle Treatment of Ni-based Alloy 8252017Ingår i: Steel Research International, ISSN 1611-3683, E-ISSN 1869-344X, Vol. 88, nr 12, artikel-id 1700165Artikel i tidskrift (Refereegranskat)
  • 152.
    Kellner, Hans
    et al.
    Högskolan Dalarna, Akademin Industri och samhälle, Materialteknik. KTH.
    Karasev, Andrey Vladimirovich
    KTH Royal Inst Technol, S-10044 Stockholm, Sweden..
    Sundqvist, Olle
    Sandvik Mat Technol AB, S-81181 Sandviken, Sweden..
    Jönsson, Pär Göran
    KTH Royal Inst Technol, S-10044 Stockholm, Sweden..
    TiN Particles and Clusters during Ladle Treatments of Ni-based Alloy 825 using Different Stirring Modes2018Ingår i: ISIJ International, ISSN 0915-1559, E-ISSN 1347-5460, Vol. 58, nr 2, s. 292-298Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Today, titanium is often used in steelmaking not only for deoxidation but also for micro-alloying and alloying for a wide range of steel grades. Therefore, many studies are focused on investigations on the formation and behavior of Ti-containing non-metallic inclusions (such as oxides, nitrides and carbides) during production of different Ti-containing steels and their effect on final steel properties. This study has examined the behavior of TiN clusters and particles in the melt during the ladle treatment of Alloy 825 containing up to 1.2 wt% of Ti. The industrial trials were performed at the end of the ladle treatment by using argon gas in combination with electromagnetic stirring using an upwards or a downwards stirring direction. Metal samples were taken before and after ladle treatment to enable three-dimensional investigations of non-metallic inclusions and clusters. The composition, size and number of particles and clusters were determined after electrolytic extraction of the metal samples by using SEM in combination with EDS. It was found that agglomerations of TiN clusters and particles in the melt are faster during an upwards stirring in comparison to a downwards stirring. However, the removal of clusters from the melt is more effective when using a downwards stirring direction compared to when using an upwards stirring in combination with gas stirring. It was also found that the Turbulent collision is the dominant factor for the agglomeration of TiN particles in the melt.

  • 153.
    Keränen, Elias
    Högskolan Dalarna, Akademin Industri och samhälle, Materialvetenskap.
    Experimental and modelling ofmachining behavior of stainlesssteel in interrupted cutting withcoated cemented carbide2014Självständigt arbete på avancerad nivå (masterexamen), 20 poäng / 30 hpStudentuppsats (Examensarbete)
    Abstract [en]

    Understanding the chip formation process and the loads that the tools are subjected to in intermittent cutting operations of stainless steel are of importance in order to increase the span of the tool life. Examples of improvements that would follow an increased tool life are reduced use of materials, decreased energy consumption, increased productivities and increased quality of the finished product.A study has been carried out to increase the understanding of chip formation process and what conditions the cutting tool is exposed to in metal cutting in the stainless steel 316L under intermittent conditions. Wear and wear rates of the cutting tools used in these conditions are determined by mechanical and thermal fatigue caused by the stress and temperature cycles. A number of different substrates with varying carbide grain size and cobalt content were included to find the beneficial properties of the cemented carbide. The study includes both practical cutting tests and simulations done in AdvantEdge with varying feed and cutting speed.A preliminary version of a power law based temperature dependent model including damage evolution has been proposed. The model was able to predict chip segmentation but failed to capture the non-linear relation between segmentation parameters and cutting speed.Simulations showed that the tool exit generates tensile stresses in the rake face of the tool which may result in fracture of the cutting edge. These stresses are caused by the footing phenomena that alter the chip formation momentarily during the tool exit.Tests also showed that it is difficult to predict tool life in milling operations of the stainless steel 316L. Chipping proved to be a dominant wear mechanism of the cemented carbide. Tough substrates with a coarse grain size and high cobalt content proved to be beneficial in terms of wear rates and tool life.

  • 154.
    Khoshkhoo, Mohsen Samadi
    et al.
    IFW Dresden, Institut für Komplexe Materialien, Postfach 27 01 16, D-01171 Dresden, Germany.
    Scudino, Sergio
    IFW Dresden, Institut für Komplexe Materialien, Postfach 27 01 16, D-01171 Dresden, Germany.
    Thomas, Jürgen
    IFW Dresden, Institut für Komplexe Materialien, Postfach 27 01 16, D-01171 Dresden, Germany.
    Surreddi, Kumar Babu
    IFW Dresden, Institut für Komplexe Materialien.
    Eckert, Jürgen
    IFW Dresden, Institut für Komplexe Materialien, Postfach 27 01 16, D-01171 Dresden, Germany.
    Grain and crystallite size evaluation of cryomilled pure copper2011Ingår i: Journal of Alloys and Compounds, ISSN 0925-8388, E-ISSN 1873-4669, Vol. 509, s. S343-S347Artikel i tidskrift (Refereegranskat)
  • 155.
    Khraisat, Walid
    Högskolan Dalarna, Akademin Industri och samhälle, Materialteknik.
    Graphite pore filling and surface blistering of sintered Fe-C-Si2012Ingår i: Powder Metallurgy, ISSN 0032-5899, E-ISSN 1743-2901, Vol. 55, nr 3, s. 242-247Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Different alloys of the system Fe-C-Si were sintered to obtain a grey iron microstructure and then hardened by post-sintering heat treatment to obtain a martensitic structure. The main problem in the development of this approach is related to the occurrence of surface blistering in the as sintered material when sintering in N2 atmosphere. Surface blistering is explained by the increase in entrapped gas pressure in pores caused by graphite pore filling. A mechanism has been proposed to explain graphite pore filling. According to this mechanism, graphite pore filling is caused by the C activity difference between the gas entrapped in pores and the matrix, which is a consequence of Boudouard’s reaction. This difference in C activity causes C to diffuse from the matrix to the pores, thus filling pores with graphite. © 2012 Institute of Materials, Minerals and Mining.

  • 156.
    Kolvereid, Anneli
    Högskolan Dalarna, Akademin Industri och samhälle, Materialteknik.
    Framtagande av fördelningsfaktorer för säkrare beräkning vid skrotlastning2014Självständigt arbete på grundnivå (kandidatexamen), 10 poäng / 15 hpStudentuppsats (Examensarbete)
    Abstract [sv]

    Detta arbete är utfört på Ovako Sweden AB i Hofors som en examinationsuppgift för ingenjörsutbildning i materialteknik. I stålindustrin är kostnaden för råvaror såsom skrot och legeringar den överlägset största och något som kräver hjälpmedel för att utnyttja på bästa sätt. Genom att använda ett optimeringsprogram vid lastning av skrot går det att gör stora besparingar. I examensarbetet presenteras framtagande av fördelningsfaktorer för säkrare beräkning vid skrotlastning. Dessa faktorer används i optimeringsprogrammet RAWMATMIX då det vid lastning av skrot går att göra besparingar genom att programmet väljer det mest ekonomiskt fördelaktiga råmaterialet. Resultaten visar att fördelningsfaktorerna skiljer sig åt mellan olika skrotklasser vilket medför att en ny fördelningsmodell måste tas fram för varje klass. Vidare måste optimeringsprogrammet anpassas för körning med ”sump” dvs. den mängd stål från föregående charge som är kvar i ljusbågsugnen.

  • 157. Larsson, C.
    et al.
    Holden, T. M.
    Bourke, M. A. M.
    Stout, M.
    Teague, J.
    Lindgren, Lars-Erik
    Högskolan Dalarna, Akademin Industri och samhälle, Materialteknik.
    Measurement andniodeling of residual stress in a welded Haynes (R) 25 cylinder2005Ingår i: Materials Science & Engineering: A, ISSN 0921-5093, E-ISSN 1873-4936, Vol. 399, nr 1-2, s. 49-57Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    An experimental and simulation study of residual stresses was made in the vicinity of a gas tungsten arc weld, used to join a hemispherical end cap to a cylinder. The capped cylinder is used in a satellite application and was fabricated from a Co-based Haynese (R) 25 alloy. The cylinder was 34.7 mm in outer diameter and 3.3 mm in thickness. The experimental measurements were made by neutron diffraction and the simulation used the implicit Marc finite element code. The experimental resolution was limited to approximately 3 rum parallel to the axis of the cylinder (the weld was 6 mm in the same direction) and comparison over the same volume of the finite element prediction showed general agreement. Subject to the limited spatial resolution, the largest experimentally measured tensile residual stress was 180 MPa, located at the middle of the weld. However, the predictions suggest that there are regions in the weld where average tensile residual stresses as much as 400 MPa exist. One qualitative disparity between the model and the experiments was that the measurement included a larger degree of asymmetry on either side of the weld than predicted by the model. 

  • 158. Lindgren, L. -E
    et al.
    Gyhlesten Back, Jessica
    Högskolan Dalarna, Akademin Industri och samhälle, Materialteknik.
    Elastic properties of ferrite and austenite in low alloy steels versus temperature and alloying2019Ingår i: Materialia, ISSN 2589-1529, Vol. 5, artikel-id 100193Artikel i tidskrift (Refereegranskat)
  • 159.
    Lindgren, Lars-Erik
    et al.
    Högskolan Dalarna, Akademin Industri och samhälle, Materialteknik.
    Domkin, Konstantin
    Högskolan Dalarna, Akademin Industri och samhälle, Maskinteknik.
    Hansson, Sofia
    Dislocations, vacancies and solute diffusion in physical based plasticity model for AISI 316L2008Ingår i: Mechanics of materials (Print), ISSN 0167-6636, E-ISSN 1872-7743, Vol. 40, nr 11, s. 907-919Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    A physical based model for the evolution of flow stress of AISI 316L from room temperature up to 1300 °C, strains up to 0.6 and strain rates from 0.0005 up to 10 s-1 is developed. One set of tests have been used for model calibration and another more complex set of tests for its validation. The model is based on a coupled set of evolution equations for dislocation density and (mono) vacancy concentration. Furthermore, it includes the effect of diffusing solutes in order to describe dynamic strain ageing (DSA). The model described the overall flow stress evolution well with exception of the details of the effect of the DSA phenomenon. Its numerical solution is implemented in a format suitable for large-scale finite element simulations.

  • 160.
    Lindgren, Lars-Erik
    et al.
    Högskolan Dalarna, Akademin Industri och samhälle, Materialvetenskap.
    Olsson, Mikael
    Högskolan Dalarna, Akademin Industri och samhälle, Materialvetenskap.
    Carlsson, Per
    Högskolan Dalarna, Akademin Industri och samhälle, Materialvetenskap.
    Simulation of hydroforming of steel tube made of metastable stainless steel2010Ingår i: International journal of plasticity, ISSN 0749-6419, E-ISSN 1879-2154, Vol. 26, nr 11, s. 1576-1590Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The Olson-Cohen model for strain-induced deformation, further developed by Stringfellow and others, has been calibrated together with a flow stress model for the plastic deformation of metastable stainless steel. Special validation tests for checking one of the limitations of the model have also been carried out. The model has been implemented into a commercial finite element code using a staggered approach for integrating the stress-strain relations with the microstructure model. Results from a thermo-mechanical coupled simulation of hydroforming of a tube have been compared with corresponding experiments. The agreement between experimental results of radial expansion and martensite fraction and the corresponding computed results is good. 

  • 161.
    Lindgren, Michael
    Högskolan Dalarna, Akademin Industri och samhälle, Materialteknik.
    An improved model for the longitudinal peak strain in the flange of a roll formed U-channel developed by FE-analyses2007Ingår i: Steel Research International, ISSN 1611-3683, E-ISSN 1869-344X, Vol. 78, nr 1, s. 82-87Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Today one can find cold roll forming (CRF) products in many applications, for example vehicles, furniture and in the building industry. Though CRF is a well known sheet metal process, it is still not entirely understood due to the geometrically complex forming. There are several computer aided engineering (CAE) programs on the market that can assist the tool maker when designing a new CRF machine. However, they are often based on simple formulas when predicting the stress and the strain in the strip. The main objective of this study is to improve formulas for the longitudinal peak membrane strain and the deformation length when a U-channel is formed. These are important since they can be used to determine the number of forming steps and the distance between them. A twolevel factorial design is done using the finite element analysis to investigate which parameters affect the peak strain and the deformation length. The parameters are then used to build models for the peak strain and the deformation length.

  • 162.
    Lindgren, Michael
    Högskolan Dalarna, Akademin Industri och samhälle, Materialteknik.
    Cold roll forming of a U-channel made of high strength steel2007Ingår i: Journal of Materials Processing Technology, ISSN 0924-0136, E-ISSN 1873-4774, Vol. 186, nr 1-3, s. 77-81Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Cold roll forming is a bending process where the bending occurs gradually in several forming steps from an undeformed strip to a finished profile. The process is very interesting for the sheet metal industry due to the high speed in which the profile can be produced. High strength steel has, in recent years, become more common in cold roll forming. These materials have advantages but also disadvantages that affect the design of the process. Simple models in literature [K.F. Chiang, Cold roll forming, ME Thesis, University of Auckland, August 1984] predict that the longitudinal peak membrane strain in the flange of a profile is independent of the material properties. However, Ingvarsson [L. Ingvarsson, F¨orenklad teori f¨or rullforming av element¨ar v-profil, j¨amf¨orelse mellan normalt och h¨ogh°allfast st°al, VAMP 15- rullforming 23 april 2001] compared mild and ultra high strength in a roll forming experiment and the conclusion was that the material properties will affect the finished profile. This paper is a fundamental study performed in order to understand the observation by Ingvarsson [L. Ingvarsson, F¨orenklad teori f¨or rullforming av element¨ar v-profil, j¨amf¨orelse mellan normalt och h¨ogh°allfast st°al, VAMP 15- rullforming 23 april 2001]. The objectives of this study are to investigate the change in the longitudinal peak membrane strain at the flange edge and the deformation length when the yield strength increases. These are important since they can be used to determine the number of forming steps and the distance between them when designing the cold roll forming machine. The result from the simulations show that the longitudinal peak membrane strain decreases and the deformation length increases when the yield strength is increased.

  • 163.
    Lindgren, Michael
    Högskolan Dalarna, Akademin Industri och samhälle, Materialteknik.
    Experimental and computational investigation of the roll forming process2009Doktorsavhandling, monografi (Övrigt vetenskapligt)
    Abstract [en]

    One of the first questions to consider when designing a new roll forming line is the number of forming steps required to produce a profile. The number depends on material properties, the cross-section geometry and tolerance requirements, but the tool designer also wants to minimize the number of forming steps in order to reduce the investment costs for the customer. There are several computer aided engineering systems on the market that can assist the tool designing process. These include more or less simple formulas to predict deformation during forming as well as the number of forming steps. In recent years it has also become possible to use finite element analysis for the design of roll forming processes. The objective of the work presented in this thesis was to answer the following question: How should the roll forming process be designed for complex geometries and/or high strength steels? The work approach included both literature studies as well as experimental and modelling work. The experimental part gave direct insight into the process and was also used to develop and validate models of the process. Starting with simple geometries and standard steels the work progressed to more complex profiles of variable depth and width, made of high strength steels. The results obtained are published in seven papers appended to this thesis. In the first study (see paper 1) a finite element model for investigating the roll forming of a U-profile was built. It was used to investigate the effect on longitudinal peak membrane strain and deformation length when yield strength increases, see paper 2 and 3. The simulations showed that the peak strain decreases whereas the deformation length increases when the yield strength increases. The studies described in paper 4 and 5 measured roll load, roll torque, springback and strain history during the U-profile forming process. The measurement results were used to validate the finite element model in paper 1. The results presented in paper 6 shows that the formability of stainless steel (e.g. AISI 301), that in the cold rolled condition has a large martensite fraction, can be substantially increased by heating the bending zone. The heated area will then become austenitic and ductile before the roll forming. Thanks to the phenomenon of strain induced martensite formation, the steel will regain the martensite content and its strength during the subsequent plastic straining. Finally, a new tooling concept for profiles with variable cross-sections is presented in paper 7. The overall conclusions of the present work are that today, it is possible to successfully develop profiles of complex geometries (3D roll forming) in high strength steels and that finite element simulation can be a useful tool in the design of the roll forming process.

  • 164. Lindgren, Michael
    et al.
    Bexell, Ulf
    Högskolan Dalarna, Akademin Industri och samhälle, Materialteknik.
    Comparison of Roll Forming Using Different Forming Strategies and Bending2014Ingår i: IDDRG 2014, conference proceedings: Innovations for the sheet metal industry, June 1-4 2014, Paris, France / [ed] SFAR Hedi, MAILLARD André, 2014Konferensbidrag (Övrigt vetenskapligt)
  • 165.
    Lindgren, Michael
    et al.
    Högskolan Dalarna, Akademin Industri och samhälle, Materialvetenskap.
    Bexell, Ulf
    Högskolan Dalarna, Akademin Industri och samhälle, Materialteknik.
    Wikström, Lars
    Roll forming of partially heated cold rolled stainless steel2009Ingår i: Journal of Materials Processing Technology, ISSN 0924-0136, E-ISSN 1873-4774, Vol. 209, nr 7, s. 3117-3124Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Today you will find roll formed details in many different products, for example buildings, household appliances and vehicles. The industry, in order to save weight, tends to use more and more high strength steel. The disadvantage with these materials is that they can be difficult to form due to reduced ductility. A way to increase the ductility in the forming areas is by partially heat the steel. It is shown that partial heating substantially increases the ductility of high strength steel and make it possible to roll form large bend angles. When roll forming, the material will work hardening almost to the as-received condition in the outer and inner radius of the roll formed profile. Furthermore, the heating power decides the bend angle obtained. Finally, the mechanical properties after heating and roll forming are discussed.

  • 166.
    Lindgren, Michael
    et al.
    Högskolan Dalarna, Akademin Industri och samhälle, Materialteknik.
    Edberg, Jonas
    Lindgren, Lars-Erik
    Roll forming2015Ingår i: Handbook of Manufacturing Engineering and Technology, Springer-Verlag London Ltd , 2015, s. 285-307Kapitel i bok, del av antologi (Övrigt vetenskapligt)
    Abstract [en]

    Roll forming is cost-effective compared to other sheet metal forming processes for uniform profiles. The process has during the last 10 years developed into forming of profiles with varying cross sections and is thereby becoming more flexible. The motion of the rolls can now be controlled with respect to many axes enabling a large variation in the profiles along the formed sheet, the so-called 3D roll forming or flexible roll forming technology. The roll forming process has also advantages compared to conventional forming for high-strength materials. Furthermore, computer tools supporting the design of the process have also been developed during the last 10 years. This is quite important when designing the forming of complex profiles. The chapter describes the roll forming process, particularly from the designer’s perspective. It gives the basic understanding of the process and how it is designed. Furthermore, modern computer design and simulation tools are discussed. © Springer-Verlag London 2015. All rights reserved.

  • 167. Lindgren, Michael
    et al.
    Ingmarsson, Lars-Olof
    3D roll-forming of hat-profile with variable depth and width2009Ingår i: Rollform09 1st International congress on roll forming, Bilbao, Spain, 2009Konferensbidrag (Övrigt vetenskapligt)
    Abstract [en]

    The use of roll-formed products in automotive, furniture, buildings etc. increases every year due to the low part-production cost and the complicated cross-sections that can be produced. The limitation with roll-forming until recent years is that one could only produce profiles with a constant cross-section in the longitudinal direction. About eight years ago ORTIC AB [1] developed a machine in which it was possible to produce profiles with a variable width (“3D roll-forming”) for the building industry. Experimental equipment was recently built for research and prototyping of profiles with variable cross-section in both width and depth for the automotive industry. The objective with the current study is to investigate the new tooling concept that makes it possible to roll-form hat-profiles, made of ultra high strength steel, with variable cross-section in depth and width. The result shows that it is possible to produce 3D roll-formed profiles with close tolerances.

  • 168. Lissel, Linda
    et al.
    Engberg, Göran
    Högskolan Dalarna, Akademin Industri och samhälle, Materialvetenskap.
    Prediction of the microstructural evolution during hot strip rolling of Nb microalloyed steels2007Ingår i: Materials Science Forum, ISSN 0255-5476, E-ISSN 1662-9752, Vol. 558-559, nr 2, s. 1127-1132Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    A physically based model is used to describe the microstructural evolution of Nb microalloyed steels during hot rolling. The model is based on a physical description of dislocation density evolution, where the generation and recovery of dislocations determines the flow stress and also the driving force for recrystallization. In the model, abnormally growing subgrains are assumed to be the nuclei of recrystallized grains and recrystallization starts when the subgrains reach a critical size and configuration. The model is used to predict the flow stress during rolling in SSAB Tunnplåt’s hot strip mill. The predicted flow stress in each stand was compared to the stresses calculated by a friction-hill roll-force model. Good fit is obtained between the predicted values by the microstructure model and the measured mill data, with an agreement generally within the interval ±15%.

  • 169.
    Ljungberg, Adam
    et al.
    Högskolan Dalarna, Akademin Industri och samhälle, Materialteknik.
    Schmidt, Nathalie
    Högskolan Dalarna, Akademin Industri och samhälle, Materialteknik.
    Deformationsstrukturer i ett duplext rostfritt stål (SAF 2507)2014Självständigt arbete på grundnivå (kandidatexamen), 10 poäng / 15 hpStudentuppsats (Examensarbete)
    Abstract [sv]

    För att kunna förbättra processer och användning av det duplexa rostfria stålet SAF 2507 måste dess deformationsegenskaper undersökas och förklaras. Genom EBSD-analyser har deformationsstrukturer och polfgurer tagits fram för att kunna beskriva materialets beteende vid deformation. Även Taylorfaktorer, E-moduler och Poissons tal har tagits fram för att kunna undersöka materialets anisotropi.

    Experimenten har utförts på prov av SAF 2507 som har deformerats plastiskt till olika töjningar. Det som undersökts är odeformerat prov, prov som dragits enaxligt till 7,7 % och 24,3 % töjning, samt ett prov som är cykliskt belastat till 3 % töjning. Det undersökta stålet tillverkas genom två olika metoder, men i denna rapport har enbart det extruderade stålet undersökts.

    Genom att jämföra hur stålets olika mekaniska egenskaper beter sig under plastisk deformation har resultatet blivit att stålets ferritfas beter sig anisotropt med en antydan till ökande isotropi vid ökande deformation. Austenitfasen beter sig däremot isotropt och blir varken mer eller mindre isotropt vid ökande deformation. Substrukturerna i ferritfasen ökar tydligt vid ökande deformation, och ses framför allt i austenitfasen efter 24 % deformation.

  • 170.
    Malakizadi, Amir
    et al.
    Department of Materials and Manufacturing Technology, Chalmers University of Technology, Gothenburg, Sweden .
    Cedergren, Stefan
    Department of Materials and Manufacturing Technology, Chalmers University of Technology, Gothenburg, Sweden .
    Surreddi, Kumar Babu
    Nyborg, Lars
    Department of Materials and Manufacturing Technology, Chalmers University of Technology, Gothenburg, Sweden .
    A methodology to evaluate the machinability of Alloy 718 by means of FE simulation2013Ingår i: International Conference on Advanced Manufacturing Engineering and Technologies. Stockholm: NEWTECH, 2013, s. 95-106Konferensbidrag (Refereegranskat)
  • 171. Malmberg, P.
    et al.
    Bexell, Ulf
    Högskolan Dalarna, Akademin Industri och samhälle, Materialvetenskap.
    Eriksson, C.
    Nygren, H.
    Richter, K.
    Analysis of bone minerals by time-of-flight secondary ion mass spectrometry: a comparative study using monoatomic and cluster ions sources2007Ingår i: Rapid Communications in Mass Spectrometry, ISSN 0951-4198, E-ISSN 1097-0231, Vol. 21, nr 5, s. 745-749Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Time-of-flight secondary ion mass spectrometry (TOF-SIMS) is an important tool for the analysis of bone minerals at implant surfaces. Most studies have been performed with monoatomic primary ion sources such as Ga+ with poor secondary molecular ion production efficiency and only elemental distributions and minor fragments of bone minerals have been reported. By using cluster ion sources, such as Au and Bi, identification of larger hydroxyapatite species at m/z 485, 541, 597 and 653, identified as Ca5P3O12, Ca6P3O13, Ca7P3O14 and Ca8P3O15, respectively, became possible. The ions appear to be fragments of the hydroxyapatite unit cell Ca10(PO4)6(OH)2. Each ion in the series is separated by 55.9 m/z units, corresponding to CaO, and this separation might reflect the columnar nature of the unit cell. Copyright © 2007 John Wiley & Sons, Ltd.

  • 172.
    Memarpour, Arashk
    Högskolan Dalarna, Akademin Industri och samhälle, Materialteknik.
    An Experimental Study of Submerged Entry Nozzles (SEN) Focusing on Decarburization and Clogging2011Doktorsavhandling, sammanläggning (Övrigt vetenskapligt)
    Abstract [en]

    The submerged entry nozzle (SEN) is used to transport the molten steel from a tundish to a mould. The main purpose of its usage is to prevent oxygen and nitrogen pick-up by molten steel from the gas. Furthermore, to achieve the desired flow conditions in the mould. Therefore, the SEN can be considered as a vital factor for a stable casting process and the steel quality. In addition, the steelmaking processes occur at high temperatures around 1873 K, so the interaction between the refractory materials of the SEN and molten steel is unavoidable. Therefore, the knowledge of the SEN behaviors during preheating and casting processes is necessary for the design of the steelmaking processes  The internal surfaces of modern SENs are coated with a glass/silicon powder layer to prevent the SEN graphite oxidation during preheating. The effects of the interaction between the coating layer and the SEN base refractory materials on clogging were studied. A large number of accretion samples formed inside alumina-graphite clogged SENs were examined using FEG-SEM-EDS and Feature analysis. The internal coated SENs were used for continuous casting of stainless steel grades alloyed with Rare Earth Metals (REM). The post-mortem study results clearly revealed the formation of a multi-layer accretion. A harmful effect of the SENs decarburization on the accretion thickness was also indicated. In addition, the results indicated a penetration of the formed alkaline-rich glaze into the alumina-graphite base refractory. More specifically, the alkaline-rich glaze reacts with graphite to form a carbon monoxide gas. Thereafter, dissociation of CO at the interface between SEN and molten metal takes place. This leads to reoxidation of dissolved alloying elements such as REM (Rare Earth Metal). This reoxidation forms the “In Situ” REM oxides at the interface between the SEN and the REM alloyed molten steel. Also, the interaction of the penetrated glaze with alumina in the SEN base refractory materials leads to the formation of a high-viscous alumina-rich glaze during the SEN preheating process. This, in turn, creates a very uneven surface at the SEN internal surface. Furthermore, these uneven areas react with dissolved REM in molten steel to form REM aluminates, REM silicates and REM alumina-silicates.

    The formation of the large “in-situ” REM oxides and the reaction of the REM alloying elements with the previously mentioned SEN´s uneven areas may provide a large REM-rich surface in contact with the primary inclusions in molten steel. This may facilitate the attraction and agglomeration of the primary REM oxide inclusions on the SEN internal surface and thereafter the clogging. The study revealed the disadvantages of the glass/silicon powder coating applications and the SEN decarburization.

    The decarburization behaviors of Al2O3-C, ZrO2-C and MgO-C refractory materials from a commercial Submerged Entry Nozzle (SEN), were also investigated for different gas atmospheres consisting of CO2, O2 and Ar. The gas ratio values were kept the same as it is in a propane combustion flue gas at different Air-Fuel-Ratio (AFR) values for both Air-Fuel and Oxygen-Fuel combustion systems. Laboratory experiments were carried out under nonisothermal conditions followed by isothermal heating. The decarburization ratio (α) values of all three refractory types were determined by measuring the real time weight losses of the samples. The results showed the higher decarburization ratio (α) values increasing for MgO-C refractory when changing the Air-Fuel combustion to Oxygen-Fuel combustion at the same AFR value. It substantiates the SEN preheating advantage at higher temperatures for shorter holding times compared to heating at lower temperatures during longer holding times for Al2O3-C samples. Diffusion models were proposed for estimation of the decarburization rate of an Al2O3-C refractory in the SEN.

    Two different methods were studied to prevent the SEN decarburization during preheating: The effect of an ZrSi2 antioxidant and the coexistence of an antioxidant additive and a (4B2O3 ·BaO) glass powder on carbon oxidation for non-isothermal and isothermal heating conditions in a controlled atmosphere. The coexistence of 8 wt% ZrSi2 and 15 wt% (4B2O3 ·BaO) glass powder of the total alumina-graphite refractory base materials, presented the most effective resistance to carbon oxidation. The 121% volume expansion due to the Zircon formation during heating and filling up the open pores by a (4B2O3 ·BaO) glaze during the green body sintering led to an excellent carbon oxidation resistance.

    The effects of the plasma spray-PVD coating of the Yttria Stabilized Zirconia (YSZ) powder on the carbon oxidation of the Al2O3-C coated samples were investigated. Trials were performed at non-isothermal heating conditions in a controlled atmosphere. Also, the applied temperature profile for the laboratory trials were defined based on the industrial preheating trials. The controlled atmospheres consisted of CO2, O2 and Ar. The thicknesses of the decarburized layers were measured and examined using light optic microscopy, FEG-SEM and EDS. A 250-290 μm YSZ coating is suggested to be an appropriate coating, as it provides both an even surface as well as prevention of the decarburization even during heating in air. In addition, the interactions between the YSZ coated alumina-graphite refractory base materials in contact with a cerium alloyed molten stainless steel were surveyed. The YSZ coating provided a total prevention of the alumina reduction by cerium. Therefore, the prevention of the first clogging product formed on the surface of the SEN refractory base materials. Therefore, the YSZ plasma-PVD coating can be recommended for coating of the hot surface of the commercial SENs.

  • 173.
    Memarpour, Arashk
    et al.
    Högskolan Dalarna, Akademin Industri och samhälle, Materialvetenskap.
    Brabie, Voicu
    Högskolan Dalarna, Akademin Industri och samhälle, Materialvetenskap.
    Jönsson, Pär
    Studies of effect of glass/silicon powder coatings on clogging behaviour of submerged entry nozzles when using REM alloyed stainless steels2011Ingår i: Ironmaking & steelmaking, ISSN 0301-9233, E-ISSN 1743-2812, Vol. 38, nr 3, s. 229-239Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The internal surfaces of modern submerged entry nozzles (SENs) were coated with a glass/silicon powder layer to prevent SEN graphite oxidation during preheating. The effects of the interaction between the coating layer and the SEN base refractory materials on clogging were studied. The results indicated that penetration of the formed alkaline rich glaze into the alumina/graphite base refractory occurs during preheating. More specifically, the glaze reacts with graphite to form carbon monoxide gas. Thereafter, dissociation of CO at the SEN/molten metal interface takes place. This leads to reoxidation of dissolved rare earth metals, which form ‘in situ’ rare earth metal oxides at the interface between the SEN and the molten steel. In addition, the interaction of the penetrated glaze with alumina in the SEN base refractory materials leads to the formation of a high viscous alumina rich glaze during the SEN preheating process. This, in turn, creates a very uneven surface at the SEN internal surface. The ‘in situ’ formation of the rare earth metal oxides together with the uneven internal surface of the SEN may facilitate the accumulation of the primary inclusions on the refractory walls.

  • 174.
    Memarpour, Arashk
    et al.
    Högskolan Dalarna, Akademin Industri och samhälle, Materialvetenskap.
    Brabie, Voicu
    Jönsson, Pär
    Studies of Yttria Stabilized Zirconia (YSZ) plasma-PVD coated Al2O3-C refractory base materials of a commercial SEN with respect todecarburization and clogging2011Ingår i: Steel Grips - Journal of Steel and Related Materials, ISSN 1866-8453Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Carbon oxidation is a main industrial problem for alumina-graphite refractory base materials used in commercial Submerged Entry Nozzles (SEN) during preheating. Thus, the effects of the plasma spray-PVD coating of the Yttria Stabilized Zirconia (YSZ) powder on the carbon oxidation were investigated. Laboratory preheating trials were performed at non-isothermal heating conditions in a controlled atmosphere. Also, the applied temperature profile for the laboratory trials were defined based on industrial preheating trials. The controlled atmospheres consisted of CO2, O2 and Ar. The (CO2/O2) ratios were kept the same as for a propane combustion flue gas at an Air-Fuel-Ratio (AFR) value equal to 1.5 for heating in an air-fuel mixture and in air. The thicknesses of the decarburized layers were measured and examined using light optic microscopy, FEG-SEM and EDS. The YSZ plasma-PVD coated alumina-graphite refractory base materials, presented the effective resistance to carbon oxidation at different coating thicknesses from 160-480 μm in both combustion flue gas and air atmospheres. For the YSZ plasma coating that contained a thinner coating layer such as 160 μm, the uneven surface of the substrate may be reflected more than it could be reflected for a thicker coating. However, for the YSZ plasma coating with a coating thickness of 290 μm, the uneven surface of the substrate may be reflected much less than it could be reflected for thinner coatings. A 250μm and a 290μm YSZ coating may prevent the decarburization of an alumina-graphite refractory base materials during preheating in air at a maximum heating temperature of 1020°C. Moreover, in an oxidizing atmosphere with an AFR value equal to 1.5 at a maximum temperature of 1020°C and a holding time of 7200 seconds. A 250-290 μm YSZ coating is suggested to be an appropriate coating, as it provides both an even surface and prevention of the decarburization even during heating in air. In addition, the interactions between the YSZ coated alumina-graphite refractory base materials in contact with a cerium alloyed molten stainless steel were surveyed. The YSZ coating provided a total prevention of the alumina reduction by cerium. Therefore, the prevention of the first clogging product formed on the surface of the SEN refractory base materials. Therefore, the YSZ plasma-PVD coating can be recommended for coating of the hot surface of thecommercial SENs.

  • 175.
    Memarpour, Arashk
    et al.
    Högskolan Dalarna, Akademin Industri och samhälle, Materialvetenskap.
    Brabie, Voicu
    Jönsson, Pär G.
    Decarburization and clogging behaviour of yttria stabilized zirconia coatings applied to SEN´s Al2O3-C refractories by plasma PVD2012Ingår i: Steel Grips - Journal of Steel and Related Materials, ISSN 1611-4442, E-ISSN 1866-8453, Vol. 10, s. 353-363Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Carbon oxidation is a main industrial problem for alumina-graphite refractory base materials used in commercial Submerged Entry Nozzles (SEN) during preheating. Thus, the effects of the plasma spray-PVD coating of the Yttria Stabilized Zirconia (YSZ) powder on the carbon oxidation were investigated. Laboratory preheating trials were performed at non-isothermal heating conditions in a controlled atmosphere. Also, the applied temperature profile for the laboratory trials were defined based on industrial preheating trials. The controlled atmospheres consisted of CO2, O2 and Ar. The (CO2/O2) ratios were kept the same as for a propane combustion flue gas at an Air-Fuel-Ratio (AFR) value equal to 1.5 for heating in an air-fuel mixture and in air. The thicknesses of the decarburized layers were measured and examined using light optic microscopy, FEG-SEM and EDS. The YSZ plasma-PVD coated alumina-graphite refractory base materials, presented the effective resistance to carbon oxidation at different coating thicknesses from 160-480 µm in both combustion flue gas and air atmospheres. For the YSZ plasma coating that contained a thinner coating layer such as 160 µm, the uneven surface of the substrate may be reflected more than it could be reflected for a thicker coating. However, for the YSZ plasma coating with a coating thickness of 290 µm, the uneven surface of the substrate may be reflected much less than it could be reflected for thinner coatings. A 250µm and a 290µm YSZ coating may prevent the decarburization of an alumina-graphite refractory base materials during preheating in air at a maximum heating temperature of 1020°C. Moreover, in an oxidizing atmosphere with an AFR value equal to 1.5 at a maximum temperature of 1020°C and a holding time of 7200 seconds. A 250-290 µm YSZ coating is suggested to be an appropriate coating, as it provides both an even surface and prevention of the decarburization even during heating in air. In addition, the interactions between the YSZ coated alumina-graphite refractory base materials in contact with a cerium alloyed molten stainless steel were surveyed. The YSZ coating provided a total prevention of the alumina reduction by cerium. Therefore, the prevention of the first clogging product formed on the surface of the SEN refractory base materials. Therefore, the YSZ plasma-PVD coating can be recommended for coating of the hot surface of the commercial SENs.

  • 176.
    Memarpour, Arashk
    et al.
    Högskolan Dalarna, Akademin Industri och samhälle, Materialvetenskap.
    Brabie, Voicu
    Högskolan Dalarna, Akademin Industri och samhälle, Materialvetenskap.
    Jönsson, Pär G.
    Post-mortem study of the internal coated SENs (Submerged Entry Nozzle) respecting clogging phenomena2011Konferensbidrag (Refereegranskat)
    Abstract [en]

    A large number of accretion samples formed inside alumina/graphite clogged Submerged Entry Nozzles (SEN) were examined using FEG-SEM-EDS and Feature analysis. The SENs were used for continuous casting of stainless steel grades alloyed by Rare Earth Metals (REM). The internal surfaces of the SENs were coated by a glass/silicon powder layer to prevent the SEN decarburization during the preheating process. The results indicated a harmful effect of the SENs decarburization on the accretion thickness. In addition, the post-mortem results clearly revealed the formation of a multi-layer accretion. Also, the study indicated the penetration of the protecting glaze into the Alumina/graphite refractory materials. The interaction of the penetrated glaze with alumina in the SEN refractory materials leads to formation of high viscous alumina-rich glaze during the SEN preheating process. This interaction may lead to formation of an uneven surface inside the SEN. These areas consist of alumina particles, silica particles and the penetrated glaze in between. The results showed that these areas react with dissolved REM in molten steel to form REM aluminates, REM silicates and REM alumina-silicates. Furthermore, the penetration of the glaze may lead to reactions between alkalines in the glaze and the graphite. This leads to a supply of oxygen at the interface between the SEN and the molten steel. This, in turn, may lead to reoxidation of the REM alloying elements in molten steel under the formation of “in situ” REM oxides. The formation of the large “in-situ” REM oxides and the reaction of the REM alloying elements with the SEN´s uneven inside surface, may create a large REM-rich surface in contact with the primary inclusions in molten steel. This may facilitate the attraction and agglomeration of the primary REM oxides inclusions on the SEN internal surface and thereafter the clogging.

  • 177.
    Memarpour, Arashk
    et al.
    Högskolan Dalarna, Akademin Industri och samhälle, Materialvetenskap.
    Brabie, Voicu
    Högskolan Dalarna, Akademin Industri och samhälle, Materialvetenskap.
    Jönsson, Pär G.
    The effect of zirconium disilicide (ZrSi2) additions on the carbon oxidation behavior of alumina/graphite refractory materials2010Ingår i: ISIJ International, ISSN 0915-1559, E-ISSN 1347-5460, Vol. 50, nr 11, s. 1612-1621Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Carbon oxidation is a main industrial problem for Alumina/Graphite Submerged Entry Nozzles (SEN) during pre-heating. Thus, the effect of ZrSi2 antioxidants and the coexistence of antioxidant additive and (4B2O3 •BaO) glass powder on carbon oxidation were investigated at simulated non-isothermal heating conditions in a controlled atmosphere. Also, the effect of ZrSi2 antioxidants on carbon oxidation was investigated at isothermal temperatures at 1473 K and 1773 K. The specimens’ weight loss and temperature were plotted versus time and compared to each others. The thickness of the oxide areas were measured and examined using XRD, FEG-SEM and EDS. The coexistence of 8 wt% ZrSi2 and 15 wt% (4B2O3 •BaO) glass powder of the total alumina/Graphite base refractory materials, presented the most effective resistance to carbon oxidation. The 121% volume expansion due to the Zircon formation during heating and filling up the open pores by (4B2O3 •BaO) glaze during green body sintering led to an excellent carbon oxidation resistance.

  • 178.
    Michael, Lindgren
    Högskolan Dalarna, Akademin Industri och samhälle, Materialteknik.
    Experimental investigations of the roll load and roll torque when high strength steel is roll formed2007Ingår i: Journal of Materials Processing Technology, ISSN 0924-0136, E-ISSN 1873-4774, Vol. 191, nr 1-3, s. 44-47Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The cold roll forming process is a highly efficient process used to produce profiles for many applications, for example vehicles, buildings, domestic machines, etc. Therefore, its market share is increasing every year. Many of the above products are already today made of high strength steel and the usage of these materials will likely continue to increase. The objectives of this project are to find howthe roll load and roll torque are influenced by the yield strength of the material. Full-scale experiments have been performed. U-channels made of different materials from mild to ultra high strength steels have been formed. The roll torque is measured during the process using a torque sensor mounted between the tool and the power transmission. Used power is also calculated with help of the motor current. The roll load is measured with load cells mounted on both side of the roll forming tool. The experimental result will increase the understanding of the specific conditions for roll forming steels with increasing yield strength. The result can be used to support the roll machine designer to choose machine elements and power unit for these applications. Furthermore, the result can also be compared with finite element simulations in order to improve and validate simulation models.

  • 179.
    Molnar, David
    Högskolan Dalarna, Akademin Industri och samhälle, Materialteknik. KTH, Tillämpad materialfysik.
    Generalised stacking fault energy and plastic deformation of austenitic stainless steels2018Licentiatavhandling, sammanläggning (Övrigt vetenskapligt)
    Abstract [sv]

    Austenitiska rostfria stål är främst kända för sin exceptionella korrosionsbeständighet. De har en ytcentrerad kubisk (FCC) struktur som stabiliseras genom att nickel tillsätts till Fe-Cr legeringen. Fe-Cr-Ni-systemet kan utökas ytterligare genom tillsats av andra element såsom Mn, Mo, N, C, etc. för att förbättra egenskaperna. Eftersom austenitiska rostfria stål ofta används som konstruktionsmaterial är det viktigt att kunna förutsäga deras mekaniska egenskaper baserat på deras sammansättning, mikrostruktur, magnetiska tillstånd, etc.

    I denna avhandling undersöker vi det plastiska deformationsbeteendet hos austenitiska rostfria stål både teoretiskt och experimentellt. I FCC material spelar staplingsfelsenergin (SFE) en viktig roll vid förutsägelsen av deformationsmekanism. Baserat på storleken av SFE kan olika deformationsmekanismer observeras, såsom martensitbildning, tvillingbildning, dissocierad eller odissocierad dislokationsglidning. Alla dessa funktioner påverkar beteendet på olika sätt, därför är det önskvärt att kunna förutsäga deras förekomst. Legering och temperatur har stark inverkan på SFE och därmed legeringarnas mekaniska egenskaper. Flera modeller, baserade på SFE och mer nyligen på den så kallade generaliserade staplingsfelenergin (GSFE eller γ-surface), är tillgängliga för att förutsäga legeringens benägenhet till tvillingbildning och den kritiska spänning som representerar den minsta upplösta skjuvspänningen som krävs för att initiera tvillingbildning. Man kan använda ab initio beräkningar baserade på täthetsfunktionalteori (DFT) för att beräkna GSFE för austenitiska stål och härleda parametrar som twinnability och kritisk tvillingsspänning.

    Vi diskuterar effekten av staplingsfelenergi på deformationsbeteendet för två olika austenitiska rostfria stål. Vi beräknar GSFE för de valda legeringarna och baserat på olika modeller, förutsäger vi deras tendens till tvillingbildning och den kritiska tvillingsspänningen. De teoretiska förutsägelserna jämförs med resultat från dragprov och bakåtspridd elektron diffraktion (EBSD). Flera konventionella och in situ dragprov utfördes för att verifiera de teoretiska resultaten. Vi utförde EBSD-mätningar på dragprov som avbrutits vid olika töjningar och efter brott samt med in situ dragprov för att följa utvecklingen av mikrostrukturen noggrant. Vi tar hänsyn till de inre energibarriärernas roll i våra förutsägelser och presenterar ett nytt sätt att experimentellt få GSFE av austenitiska rostfria stål. Tidigare kunde endast SFE mätas tillförlitligt genom väl utformade experiment. I den aktuella avhandlingen går vi vidare och föreslår en teknik som kan ge noggranna värden för den instabila staplingsfelenergin för alla austenitiska legeringar som uppvisar tvillingbildning.

  • 180.
    Molnar, David
    Högskolan Dalarna, Akademin Industri och samhälle, Materialteknik. KTH, Tillämpad materialfysik.
    Stacking fault energy and deformation behaviour of austenitic stainless steels: a joint theoretical-experimental study2019Doktorsavhandling, sammanläggning (Övrigt vetenskapligt)
    Abstract [sv]

    Austenitiska rostfria stål är främst kända för sin exceptionella korrosionsbeständighet. De har en ytcentrerad kubisk (FCC) struktur som stabiliseras genom att nickel, mangan eller kväve tillsätts till Fe-Cr legeringen. Fe-Cr-Ni-systemet kan utökas ytterligare genom tillsats av andra element såsom Mo, Cu, Ti, C, etc. för att förbättra egenskaperna. Eftersom austenitiska rostfria stål ofta används som konstruktionsmaterial är det viktigt att kunna förutsäga deras mekaniska egenskaper baserat på deras sammansättning, mikrostruktur, magnetiska tillstånd, etc. 

    I denna avhandling är det plastiska deformationsbeteendet hos austenitiska rostfria stål undersökt med teoretiskt och experimentellt. I FCC material spelar staplingsfelsenergin (SFE) en viktig roll vid förutsägelsen och beskrivning av deformationsmekanism. Baserat på storleken av SFE kan olika deformationsmekanismer observeras, såsom martensitbildning, tvillingbildning, eller dislokationsglidning. Alla dessa funktioner påverkar beteendet, därför är det önskvärt att förutsäga och kontrollera deras förekomst. Legering och temperatur har stark inverkan på SFE och därmed legeringarnas mekaniska egenskaper. Flera modeller, baserade på SFE och mer nyligen på den så kallade generaliserade staplingsfelenergin (GSFE eller γ-surface), är tillgängliga för att förutsäga legeringens affinitet till tvillingbildning och den kritiska spänning som representerar den minsta upplösta skjuvspänningen som krävs för att initiera tvillingbildning. Man kan använda ab initio beräkningar baserade på täthetsfunktionalteori (DFT) för att beräkna GSFE för austenitiska stål och härleda parametrar som twinnability och kritisk tvillingsspänning.

    Korrelation mellan staplingsfelenergi och deformationsbeteendet för fyra olika austenitiska rostavstavning stål diskuteras i detta arbete. SFE för de valda legeringarna erhålls genom ab initio beräkningar och baserat på olika modeller, deras tendens till tvillingbildning och den kritiska tvillingsspänningen kan förutsägas. Deras mekaniska beteende och affinitet till tvilling och martensitisk transformation kartläggs över ett brett temperaturområde (−70°C to +500°C) för de fyra legeringarna. De teoretiska förutsägelserna jämförs med resultat från dragprov och bakåtspridd elektrondiffraktion (EBSD). Flera konventionella och in situ dragprov utfördes för att verifiera de teoretiska resultaten. Vi utförde EBSD-mätningar på dragprov som avbrutits vid olika töjningar och efter brott samt med in situ dragprov för att följa utvecklingen av mikrostrukturen noggrant. Vi tar hänsyn till de inre energibarriärernas roll i våra förutsägelser och presenterar ett nytt sätt att experimentellt få GSFE av austenitiska rostfria stål. Tidigare kunde endast SFE mätas tillförlitligt genom väl utformade experiment. I den aktuella avhandlingen går vi vidare och föreslår en teknik som kan ge noggranna värden för den instabila staplingsfelenergin för alla austenitiska legeringar som uppvisar tvillingbildning på låga spänningsnivåer. Betydelsen av temperatur och mellanliggande legering på mekaniskt beteende undersökt också i detta arbete.

  • 181.
    Molnar, David
    et al.
    Högskolan Dalarna, Akademin Industri och samhälle, Materialteknik. KTH.
    Engberg, Göran
    Högskolan Dalarna, Akademin Industri och samhälle, Materialteknik.
    Li, Wei
    Lu, Song
    Hedström, Peter
    Kwon, Se Kyun
    Vitos, Levente
    Experimental study of the gamma-surface of austenitic stainless steels2019Ingår i: Acta Materialia, ISSN 1359-6454, E-ISSN 1873-2453, Vol. 173, s. 34-43Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We introduce a theory-guided experimental approach to study the γ-surface of austenitic stainless steels. The γ-surface includes a series of intrinsic energy barriers (IEBs), which are connected to the unstable stacking fault (USF), the intrinsic stacking fault (ISF), the unstable twinning fault (UTF) and the extrinsic stacking fault (ESF) energies. The approach uses the relationship between the Schmid factors and the effective energy barriers for twinning and slip. The deformation modes are identified as a function of grain orientation using in situ electron backscatter diffraction measurements. The observed critical grain orientation separating the twinning and slip regimes yields the USF energy, which combined with the universal scaling law provides access to all IEBs. The measured IEBs and the critical twinning stress are verified by direct first-principles calculations. The present advance opens new opportunities for modelling the plastic deformation mechanisms in multi-component alloys.

  • 182.
    Molnar, David
    et al.
    Högskolan Dalarna, Akademin Industri och samhälle, Materialteknik. KTH.
    Engberg, Göran
    Högskolan Dalarna, Akademin Industri och samhälle, Materialteknik.
    Li, Wei
    Vitos, Levente
    Deformation properties of austenitic stainless steels with different stacking fault energies2018Ingår i: Materials Science Forum, ISSN 0255-5476, E-ISSN 1662-9752, Vol. 941, s. 190-197Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    In FCC metals a single parameter – stacking fault energy (SFE) – can help to predict the expectable way of deformation such as martensitic deformation, deformation twinning or pure dislocation glide. At low SFE one can expect the perfect dislocations to dissociate into partial dislocations, but at high SFE this separation is more restricted. The role of the magnitude of the stacking fault energy on the deformation microstructures and tensile behaviour of different austenitic steels have been investigated using uniaxial tensile testing and electron backscatter diffraction (EBSD). The SFE was determined by using quantum mechanical first-principles approach. By using plasticity models we make an attempt to explain and interpret the different strain hardening behaviour of stainless steels with different stacking fault energies.

  • 183.
    Molnar, David
    et al.
    Högskolan Dalarna, Akademin Industri och samhälle, Materialteknik. KTH.
    Sun, Xun
    Lu, Song
    Li, Wei
    Engberg, Göran
    Högskolan Dalarna, Akademin Industri och samhälle, Materialteknik.
    Vitos, Levente
    Effect of temperature on the stacking fault energy and deformation behaviour in 316L austenitic stainless steel2019Ingår i: Materials Science & Engineering: A, ISSN 0921-5093, E-ISSN 1873-4936, Vol. 759, s. 490-497Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The stacking fault energy (SFE) is often used as a key parameter to predict and describe the mechanical behaviour of face centered cubic material. The SFE determines the width of the partial dislocation ribbon, and shows strong correlation with the leading plastic deformation modes. Based on the SFE, one can estimate the critical twinning stress of the system as well. The SFE mainly depends on the composition of the system, but temperature can also play an important role. In this work, using first principles calculations, electron backscatter diffraction and tensile tests, we show a correlation between the temperature dependent critical twinning stress and the developing microstructure in a typical austenitic stainless steel (316L) during plastic deformation. We also show that the deformation twins contribute to the strain hardening rate and gradually disappear with increasing temperature. We conclude that, for a given grain size there is a critical temperature above which the critical twinning stress cannot be reached by normal tensile deformation, and the disappearance of the deformation twinning leads to lower strain hardening rate and decreased ductility.

  • 184.
    Molnar, David
    et al.
    Högskolan Dalarna, Akademin Industri och samhälle, Materialteknik. KTH.
    Vida, Ádám
    Huang, Shuo
    Chinh, Nguyen Q
    The effect of cooling rate on the microstructure and mechanical properties of NiCoFeCrGa high-entropy alloy2019Ingår i: Journal of Materials Science, ISSN 0022-2461, E-ISSN 1573-4803, Vol. 54, nr 6, s. 5074-5082Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The effect of cooling rate on the microstructure and mechanical properties of equimolar NiCoFeCrGa high-entropy alloy (HEA) was studied by scanning electron microscopy, energy-dispersive X-ray spectroscopy and electron backscatter diffraction (EBSD), as well as by microhardness tests. Experimental results show that the cooling rate has a crucial impact on the developing microstructure which has a mixture of two—FCC and BCC—phases, leading to a self-similarity of the solidified structure formed in the sample. Furthermore, the cooling rate influences both the composition of the two phase-components and the ratio of their volume fractions, determining the mechanical properties of the sample. The present results confirm the grouping of Co, Fe and Cr in the FCC phase and that of Ni and Ga in BCC phase in the NiCoFeCrGa high-entropy alloy system. An empirical rule is suggested to predict how the phase-components can be expected in this complex high-entropy alloy.

  • 185.
    Mukhopadhyay, N K
    et al.
    a Centre of Advanced Study, Department of Metallurgical Engineering, Institute of Technology, Banaras Hindu University, Varanasi 221 005, India.
    Ali, Fahad
    IFW Dresden, Institut für Komplexe Materialien, Postfach 27 01 16, D-01171 Dresden, Germany.
    Srivastava, Vikas C
    National Metallurgical Laboratory, Jamshedpur-831 007, India.
    Yadav, T P
    Department of Physics, Banaras Hindu University, Varanasi 221 005, India.
    Sakaliyska, Miroslava
    IFW Dresden, Institut für Komplexe Materialien, Postfach 27 01 16, D-01171 Dresden, Germany.
    Surreddi, Kumar Babu
    IFW Dresden, Institut für Komplexe Materialien.
    Scudino, Sergio
    IFW Dresden, Institut für Komplexe Materialien, Postfach 27 01 16, D-01171 Dresden, Germany.
    Uhlenwinkel, Volker
    Institut für Werkstofftechnik, Universität Bremen, Badgasteiner Str. 3, D-28359 Bremen, Germany.
    Eckert, Jürgen
    IFW Dresden, Institut für Komplexe Materialien, Postfach 27 01 16, D-01171 Dresden, Germany.
    Strain-induced structural transformation of single-phase Al–Cu–Fe icosahedral quasicrystal during mechanical milling2011Ingår i: Philosophical Magazine, ISSN 1478-6435, Vol. 91, nr 19-21, s. 2482-2490Artikel i tidskrift (Refereegranskat)
  • 186.
    Nikolowski, K
    et al.
    IFW Dresden, Institut für Komplexe Materialien, Postfach 27 01 16, D-01171 Dresden, Germany.
    Scudino, Sergio
    IFW Dresden, Institut für Komplexe Materialien, Postfach 27 01 16, D-01171 Dresden, Germany.
    Stoica, Mihai
    IFW Dresden, Institut für Komplexe Materialien, Postfach 27 01 16, D-01171 Dresden, Germany.
    Surreddi, Kumar Babu
    IFW Dresden, Institut für Komplexe Materialien.
    Das, Jayanta
    IFW Dresden, Institut für Komplexe Materialien, Postfach 27 01 16, D-01171 Dresden, Germany.
    Eckert, Jürgen
    IFW Dresden, Institut für Komplexe Materialien, Postfach 27 01 16, D-01171 Dresden, Germany.
    Stress-induced martensitic transformation in a Ti45Zr38Al17 cast rod2009Ingår i: Journal of Physics: Conference Series, ISSN 1742-6588, Vol. 144, nr 1, s. 1-4Artikel i tidskrift (Refereegranskat)
  • 187.
    Nilsson, Maria
    Högskolan Dalarna, Akademin Industri och samhälle, Materialteknik.
    Tribology in Metal Working2012Licentiatavhandling, sammanläggning (Övrigt vetenskapligt)
    Abstract [en]

    This thesis focuses on the tribological performance of tool surfaces in two steel working operations, namely wire drawing and hot rolling. In all forming operations dimensions and surface finish of the products are of utmost importance. Forming basically includes three parts – forming conditions excluded – that may be changed; work material, tool and (possibly) lubricant. In the interface between work material and tool, the conditions are very aggressive with – generally or locally – high temperatures and pressures. The surfaces will be worn in various ways and this will change the conditions in the process. Consequently, the surface finish as well as the dimensions of the formed product may change and in the end, the product will not fulfil the requirements of the customer. Therefore, research and development in regard to wear, and consequently tribology, of the forming tools is of great interest.

    The investigations of wire drawing dies focus on coating adhesion/cohesion, surface characteristics and material transfer onto the coated steel both in laboratory scale as well as in the wire drawing process. Results show that it in wire drawing is possible to enhance the tribological performance of drawing dies by using a lubricant together with a steel substrate coated by a polished, dual-layer coating containing both hard and friction-lowering layers.

    The investigations of hot rolling work rolls focus on microstructure and hardness as well as cracking- and surface characteristics in both laboratory scale and in the hot strip mill. Results show that an ideal hot work roll material should be made up of a matrix with high hardness and a large amount of complex, hard carbides evenly distributed in the microstructure. The surface failure mechanisms of work rolls are very complex involving plastic deformation, abrasive wear, adhesive wear, mechanical and thermal induced cracking, material transfer and oxidation.

    This knowledge may be used to develop new tools with higher wear resistance giving better performance, lower costs and lower environmental impact.

  • 188.
    Nilsson, Maria
    et al.
    Högskolan Dalarna, Akademin Industri och samhälle, Materialteknik.
    Olsson, Mikael
    Högskolan Dalarna, Akademin Industri och samhälle, Materialteknik.
    An investigation of worn work roll materials used in the finishing stands of the hot strip mill for steel rolling2012Konferensbidrag (Refereegranskat)
    Abstract [en]

    The surface failure characteristics of different work roll materials, i.e. High Speed Steel, High Chromium Iron and Indefinite Chill Iron, used in the finishing stands of a hot strip mill have been investigated using stereo microscopy, 3D optical profilometry, scanning electron microscopy and energy dispersive X-ray spectroscopy. The results show that the surface failure mechanisms of work rolls for hot rolling are very complex, involving plastic deformation, abrasive wear, adhesive wear, mechanical and thermal induced cracking, material transfer and oxidation. Despite the differences in chemical composition and microstructure, the tribological response of the different work roll materials was found to be strongly dependent on the material microstructure and especially the presence and distribution of microstructural constituents, such as the different carbide phases and graphite (in the case of Indefinite Chill Iron). Cracking and chipping of the work roll surfaces, both having a negative impact on work roll wear, are strongly influenced by the presence of carbides, carbide networks and graphite in the work roll surface. Consequently, the amount of carbide forming elements as well as the manufacturing process must be controlled in order to obtain an optimised microstructure and a predictable wear rate.

  • 189.
    Nilsson, Maria
    et al.
    Högskolan Dalarna, Akademin Industri och samhälle, Materialteknik.
    Olsson, Mikael
    Högskolan Dalarna, Akademin Industri och samhälle, Materialteknik.
    An investigation of worn work roll materials used in the finishing stands of the hot strip mill for steel rolling2013Ingår i: Proceedings of the Institution of mechanical engineers. Part J, journal of engineering tribology, ISSN 1350-6501, E-ISSN 2041-305X, Vol. 227, nr 8, s. 837-844Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The surface failure characteristics of different work roll materials, i.e. High Speed Steel, High Chromium Iron and Indefinite Chill Iron, used in the finishing stands of a hot strip mill have been investigated using stereo microscopy, 3D optical profilometry, scanning electron microscopy and energy dispersive X-ray spectroscopy. The results show that the surface failure mechanisms of work rolls for hot rolling are very complex, involving plastic deformation, abrasive wear, adhesive wear, mechanical and thermal induced cracking, material transfer and oxidation. Despite the differences in chemical composition and microstructure, the tribological response of the different work roll materials was found to be strongly dependent on second phase constituents such as the size, morphology and distribution of different carbide phases and graphite (in the case of Indefinite Chill Iron) which was found to promote cracking. Cracking and chipping of the work roll surfaces, both having a negative impact on work roll wear, are strongly influenced by the presence of carbides, carbide networks and graphite in the work roll surface. Consequently, the amount of carbide forming elements as well as the manufacturing process must be controlled in order to obtain an optimised microstructure and a predictable wear rate.

  • 190.
    Nilsson, Maria
    et al.
    Högskolan Dalarna, Akademin Industri och samhälle, Materialteknik.
    Olsson, Mikael
    Högskolan Dalarna, Akademin Industri och samhälle, Materialteknik. Tribomaterials group, The Ångström Laboratory, Uppsala University, Sweden.
    Microstructural, mechanical and tribological characterisation of roll materials for the finishing stands of the hot strip mill for steel rolling2013Ingår i: Wear, ISSN 0043-1648, E-ISSN 1873-2577, Vol. 307, nr 1-2, s. 209-217Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The microstructure, mechanical and tribologicalproperties for three different materials, High Speed Steel, High Chromium ironand Indefinite Chill iron, used for hot strip mill work rolls have beenevaluated. Microstructural characterisation was performed using light opticalmicroscopy, scanning electron microscopy and energy dispersive X-rayspectroscopy. The mechanical and tribological properties were evaluated usingmicro Vickers indentation and scratch testing in combination with post-testmicroscopy. The microstructures of the investigated materials were found to berather complex with a number of secondary phases andalso materials with similar nominal composition display significant differenceswith respect to distribution, size and morphology of carbides. Scratch testing,including detection of friction coefficient, acoustic emission and penetrationdepth, gives valuable information concerning the mechanical and tribologicalresponse on a microscopic level of the investigated materials. Type,amount, distribution, size and morphology of the secondary phases in thematerials have a strong impact on the surface deformation and wear mechanismsduring scratching. Cracking and chipping are frequently observed in connectionto the ridges surrounding the scratches. However, cross-sectional analyses ofthe scratched microstructures reveal that cracking of the brittle carbidephases may extend to significant depths, >100 µm, reducing the mechanicalstrength of the material. Based on the results, it is believed that a moreisotropic microstructure, e.g. obtained via a powder metallurgy process, withfiner carbides would result in improved properties and performance in a hotrolling application.

  • 191.
    Nilsson, Maria
    et al.
    Högskolan Dalarna, Akademin Industri och samhälle, Materialvetenskap.
    Olsson, Mikael
    Högskolan Dalarna, Akademin Industri och samhälle, Materialvetenskap.
    Tribological Testing of Some Potential PVD and CVD Coatings for Steel Wire Drawing Dies2010Ingår i: Nordtrib 2010, Storforsen, 2010Konferensbidrag (Refereegranskat)
    Abstract [en]

    Cemented carbide is today the most frequently used drawing die material in steel wire drawing applications. This is mainly due to the possibility to obtain a broad combination of hardness and toughness thus meeting the requirements concerning strength, crack resistance and wear resistance set by the wire drawing process. However, the increasing cost of cemented carbide in combination with the possibility to increase the wear resistance of steel through the deposition of wear resistant CVD and PVD coatings have enhanced the interest to replace cemented carbide drawing dies with CVD and PVD coated steel wire drawing dies. In the present study, the possibility to replace cemented carbide wire drawing dies with CVD and PVD coated steel drawing dies have been investigated by tribological characterisation, i.e. pin-on-disc and scratch testing, in combination with post-test observations of the tribo surfaces using scanning electron microscopy, energy dispersive X-ray spectroscopy and 3D surface profilometry. Based on the results obtained, CVD and PVD coatings aimed to provide improved tribological performance of steel wire drawing dies should display a smooth surface topography, a high wear resistance, a high fracture toughness (i.e. a high cracking and chipping resistance) and intrinsic low friction properties in contact with the wire material. Also, the steel substrate used must display a sufficient load carrying capacity and resistance to thermal softening. Of the CVD and PVD coatings evaluated in the tribological tests, a CVD TiC and a PVD CrC/C coating displayed the most promising results.

  • 192. Olofsson, J.
    et al.
    Bexell, Ulf
    Högskolan Dalarna, Akademin Industri och samhälle, Materialteknik.
    Jacobson, S.
    Tribofilm formation of lightly loaded self mated alumina contacts2012Ingår i: Wear, ISSN 0043-1648, E-ISSN 1873-2577, Vol. 289, s. 39-45Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    A tribofilm is formed on alumina surfaces that have been slid against alumina surfaces. The tribofilm is formed by alumina wear particles that have been ground, agglomerated and tribosintered to a film. The tribofilm smoothens out the surface topography and fills up cavities. Tribofilms on alumina surfaces have been investigated with respect to surface appearance, hardness and chemical composition. Surface preparation and surrounding humidity have shown to affect the character and lateral distribution of the tribofilm. The tribofilm that was formed in humid air was softer than the tribofilm formed in dry air. XPS analysis revealed the chemical shift of the Al 2p peak did not differ between the tribofilms that was formed in different humidity, nor the unworn reference surface, finding that no hydroxide was found on the alumina surfaces. Also, no tribochemical changes could be detected by ToF-SIMS analysis. (C) 2012 Elsevier B.V. All rights reserved.

  • 193.
    Olovsjö, S
    et al.
    Atlas Copco.
    Johanson, R
    Atlas Copco.
    Bexell, Ulf
    Högskolan Dalarna, Akademin Industri och samhälle, Materialteknik.
    Olsson, Mikael
    Högskolan Dalarna, Akademin Industri och samhälle, Materialteknik.
    On the understanding of cemented carbide degradation in rock drilling: the importance of metallographic sample preparation2012Ingår i: Proceedings of Euro PM 2012 Congress & Exhibition Vol. 2, 2012Konferensbidrag (Refereegranskat)
  • 194.
    Olovsjö, S
    et al.
    Atlas Copco.
    Johanson, R
    Atlas Copco.
    Falsafi, M
    Atlas Copco.
    Bexell, Ulf
    Högskolan Dalarna, Akademin Industri och samhälle, Materialteknik.
    Olsson, Mikael
    Högskolan Dalarna, Akademin Industri och samhälle, Materialteknik.
    Surface failure and wear of cemented carbide rock drill buttons: the importance of sample preparation and optimized microscopy settings2013Ingår i: Wear, ISSN 0043-1648, E-ISSN 1873-2577, Vol. 302, nr 1-2, s. 1546-1554Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The combination of suitable mechanical properties and wear resistance makes cemented carbide one of the most interesting engineering composite materials for tribological applications, such as in rock drilling. Despite the fact that cemented carbide buttons have been used in rock drilling applications for a long time the detailed understanding of the prevailing wear mechanisms is far from complete and wear and breakage of rock drill buttons are still one of the lifetime-limiting factors for rock drill bits. Consequently, further research in this area, including detailed characterization of worn drill button surfaces and sub-surface regions, is needed in order to support the future development of new cemented carbide grades with improved failure and wear resistance. In the present paper, high resolution scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS) and Auger electron spectroscopy (AES) have been used to characterize the wear and failure mechanisms of worn drill buttons and samples exposed to well controlled impact and scratch tests performed in the laboratory. The most important mechanisms of surface failure and wear were found to be severe plastic deformation, cracking, crushing of individual WC grains and mechanical/tribochemical degradation of the Co binder phase including Co depletion. Fracture cross-sectioning under tensile stress-state was found to be the best method for achieving large and reliable sub-surface cross-sections within a short time and to a low cost. The importance of optimized microscopy and spectroscopy settings for enhanced surface sensitivity for the examination of small-scale tribological phenomena is illuminated and discussed.

  • 195.
    Olsson, Mikael
    Högskolan Dalarna, Akademin Industri och samhälle, Materialvetenskap.
    A new test method for measuring the galling resistance between metal powders and die tool materials in powder compaction2011Ingår i: Wear, ISSN 0043-1648, E-ISSN 1873-2577, Vol. 273, nr 1, s. 49-54Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The friction characteristics and galling resistance between metal powder and die tool material in metal powder compaction is of outmost importance since they will influence the porosity and surface quality of the green body and consequently the porosity, tolerances and surface quality of the final sintered product. In the present study, a new test method for evaluating the tribological performance of die tool materials aimed for powder compaction is presented. The test method is based on controlled scratch testing using a commercial scratch tester but instead of the commonly used Rockwell C diamond stylus a sample holder with a small green body of compacted powder particles is drawn over the surface in a well controlled multi pass linear reciprocating sliding contact. The capability of the test method was evaluated for different types of tool materials including two PVD coatings in contact with different types of metal powders to determine the friction characteristics and the adhesion and material transfer tendency at the sliding interface. Post-test examination of the tool surfaces using FEG-SEM and EDS were performed in order to evaluate the mechanisms controlling the friction behavior and the material transfer tendency. The results show that the proposed test is a simple and fast method to obtain relevant data regarding the friction and galling characteristics of die tool materials in metal powder compaction. The mechanisms prevailing at the green body/die tool material interface, e.g. cold welding, can easily be monitored by the friction and acoustic emission signals. Of the die tool materials investigated the low friction PVD a-C:Cr coating displayed the lowest friction and highest galling resistance.

  • 196.
    Olsson, Mikael
    Högskolan Dalarna, Akademin Industri och samhälle, Materialteknik.
    On the use of scratch testing as a model experiment for evaluating the initial wear of cemented carbidein rock drilling2013Konferensbidrag (Refereegranskat)
  • 197.
    Olsson, Mikael
    Högskolan Dalarna, Akademin Industri och samhälle, Materialvetenskap.
    Tribological evaluation of some potential tribo materials used in column lift rolling contacts: a case study2011Ingår i: Wear, ISSN 0043-1648, E-ISSN 1873-2577, Vol. 270, nr 9-10, s. 720-724Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The friction and wear characteristics of some potential tribological pairs aimed for the wheel/rail rolling contact in column lifts were studied. Tribo tests were performed using a pin-on-disc equipment and the tribological pairs included; stainless steel against ball bearing steel, stainless steel against WC/C-coated ball bearing steel and stainless steel against cast nylon (polyamide 6). The influence of coating surface topography as well as stainless steel surface topography on the friction and wear behaviour of the tribological pairs was investigated. The results show that the WC/C-coating significantly improves the tribological performance of the stainless steel/ball bearing steel sliding couples but that the WC/C-coating show a limited life-time in sliding contact with stainless steel under the prevailing contact conditions. In contrast, the stainless steel/ball bearing steel sliding couples suffer from high friction and wear due to strong adhesion between the mating surfaces followed by metal transfer and severe adhesive wear. The stainless steel/cast nylon sliding couples show a somewhat intermediate behaviour regarding friction and wear where the friction is controlled by the generation of a polymer transfer film and wear of the cast nylon is controlled by the surface topography of the mating stainless steel surface. The results obtained are discussed in relation to the identified friction and wear mechanisms as characterized by SEM and EDX.

  • 198.
    Olsson, Mikael
    Högskolan Dalarna, Akademin Industri och samhälle, Materialteknik.
    Tråddragningens tribologi2015Ingår i: Nordisk Trådteknisk Förening: Årsbok 2015 / [ed] Leif Eriksson, NTTF , 2015Kapitel i bok, del av antologi (Övrigt vetenskapligt)
  • 199.
    Olsson, Mikael
    et al.
    Högskolan Dalarna, Akademin Industri och samhälle, Materialvetenskap.
    Bexell, Ulf
    Högskolan Dalarna, Akademin Industri och samhälle, Materialteknik.
    Friction characteristics and material transfer tendency in metal powder compaction2011Ingår i: Wear, ISSN 0043-1648, E-ISSN 1873-2577, Vol. 271, nr 9-10, s. 1903-1908Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The friction characteristics and material transfer tendency between metal powder and die tool material in metal powder compaction play an important role in the production of near-net-shape components of high density. A natural step to further increase the green density and simplify the sintering process is to reduce the amount of internal lubricant in the powder since the volume fraction of an organic lubricant will result in a significant contribution to the resulting porosity. However, this will significantly increase the adhesive contact and thus the friction between the die and the powder/green body during the powder compaction process. As a result, the compaction and ejection forces as well as the wear rate of the die and punch surfaces will increase. Consequently, improved knowledge concerning the friction mechanisms prevailing at the metal powder/die tool material interface is needed. The present paper will present data regarding the influence of type of tool and coating material on the friction characteristics and material transfer tendency during simulated powder compaction of a water atomized plain iron powder under no or starved lubrication conditions using two different laboratory tribo tests. Tool materials investigated include ingot cast tool steel, powder metallurgy (PM) tool steel and TiAlN and DLC-type PVD coatings. Post-test characterization using scanning electron microscopy and energy dispersive X-ray spectroscopy was used to analyse the tribo surfaces and especially the tendency to material transfer and tribo film formation. The results show that the material transfer tendency is mainly controlled by strong adhesive metal–metal contacts and that a PVD coating showing intrinsic low-friction properties and a smooth surface topography may significantly reduce the interaction between the mating surfaces promoting a stable friction and a low material transfer tendency.

  • 200.
    Olsson, Mikael
    et al.
    Högskolan Dalarna, Akademin Industri och samhälle, Materialteknik.
    Heinrichs, Jannica
    Yvell, Karin
    Högskolan Dalarna, Akademin Industri och samhälle, Materialteknik.
    Jacobson, Staffan
    Initial degradation of cemented carbides for rock drilling: model studies of the tribological contact against rock2015Ingår i: International journal of refractory metals & hard materials, ISSN 0958-0611, E-ISSN 2213-3917, Vol. 52, s. 104-113Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Hardness and fracture toughness are often used as the prime material parameters to characterise cemented carbides used in rock drilling. However, the deformation and wear of cemented carbide are too complicated to be described by these parameters alone. The cemented carbide and the wearing rock mineral are both composite materials, containing phases with widely varying hardness. Moreover, the deformation behaviour of the individual phases may be strongly anisotropic, as for the WC grains in the cemented carbide. The wear of the cemented carbide typically occurs on the scale of individual grains or smaller. Contrastingly, the hardness stated for both is typically a macroscopic value, averaged over numerous grains, orientations, etc. The present investigation aims to contribute to the understanding of the relations between microstructure, properties and wear mechanisms of cemented carbide buttons in rock drilling. It is focused on the role of scale of deformation in relation to size of the different phases of the cemented carbide. This is achieved by simplifying the contact situation of the rock drill button to a single stylus sliding contact between a granite stylus and a polished cemented carbide surface. The deformation and wear of this well controlled contact is then evaluated on the sub-micrometer scale; using high resolution FEG-SEM with EBSD, FIB cross-sectioning and AFM. The results show that even an extremely local deformation, such as slip within individual WC grains, affects the tribological contact, and that the nominally much softer granite may cause deformation both within individual WC grains, and on the composite scale. The results are discussed with respect to their significance for wear of cemented carbides in rock drilling. (C) 2015 Elsevier Ltd. All rights reserved.

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