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  • 101. Heinrichs, Jannica
    et al.
    Olsson, Mikael
    Högskolan Dalarna, Akademin Industri och samhälle, Materialvetenskap.
    Jacobson, Staffan
    New understanding of the initiation of material transfer and transfer layer build-up in metal forming: in situ studies in the SEM2012Ingår i: Wear, ISSN 0043-1648, E-ISSN 1873-2577, Vol. 292, s. 61-73Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The tribological mechanisms behind the initiation of material transfer and build-up of transfer layers in aluminium forming have been studied in situ in the SEM where a tip of aluminium is put into contact with a tool steel surface under controlled sliding contact conditions. By combining in situ observations with post-test high resolution FEG-SEM studies of the contacting surfaces we have shown that aluminium is immediately transferred onto the fine polished tool steel. It was also confirmed that the initial transfer occurs on a very fine scale and is localised to the surface irregularities presented by the slightly protruding carbonitrides. In contrast, the less protruding M6C carbides, as well as the martensitic steel matrix exhibit very little initial transfer. Intentionally made scratches (roughly 5 mu m wide and 2 mu m deep) across the tool surface immediately result in larger scale transfer, which grows upon further passages of work material causing a high coefficient of friction. The study illuminates the extreme value of combining the in situ technique with high-resolution scanning electron microscopy using low acceleration voltage as a mean to detect the very thin initial transfer layers. With the higher acceleration voltages normally used, the transferred aluminium becomes transparent and can hardly be detected. (C) 2012 Elsevier B.V. All rights reserved.

  • 102.
    Hoier, Philipp
    et al.
    Department of Industrial and Materials Science, Chalmers University of Technology, Gothenburg, Sweden.
    Surreddi, Kumar Babu
    Högskolan Dalarna, Akademin Industri och samhälle, Materialteknik.
    Klement, Uta
    Department of Industrial and Materials Science, Chalmers University of Technology, Gothenburg, Sweden.
    Tool wear by dissolution during machining of alloy 718 and Waspaloy: a comparative study using diffusion couples2020Ingår i: The International Journal of Advanced Manufacturing Technology, ISSN 0268-3768, E-ISSN 1433-3015, Vol. 106, nr 3-4, s. 1431-1440Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The wear of metal cutting tools is known to take place by the combined and simultaneous effects of several wear mechanisms. Knowledge of the relative contribution of the individual wear mechanisms is required to understand and predict the tool wear during cutting different workpiece materials and alloys. It has been shown previously that machining two heat resistant superalloys, alloy 718 and Waspaloy, leads to distinctively different tool wears. Even though the subject has been addressed in various studies, there are still open questions regarding the underlying reasons for the differing tool wear rates. In particular, the relative contributions of diffusion/dissolution when machining the two alloys have not been addressed so far. Therefore, a qualitative comparison of the chemical interaction between the tool material and the two superalloys was made by using diffusion couple tests. The aim was to mimic the high temperatures and intimate contact between workpiece and tool material at the tool rake and flank faces during cutting under controlled and static conditions. The obtained results suggest that it is unlikely that differences in flank wear rate when machining the two superalloys are caused by significantly varying magnitudes of tool atoms dissolving into the respective workpiece. Analysis of the tool/superalloy interfaces in the diffusion couples revealed diffusion-affected zones of similar size for both tested superalloys. Increasing test temperature led to enhanced interdiffusion which suggests an increase in tool wear by diffusion/dissolution for higher cutting temperature. For alloy 718, the higher test temperature also led to depletion of carbon together with formation of tungsten within the tool in close vicinity to the interface with the superalloy.

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  • 103. Hooshyar, H.
    et al.
    Jonsson, T.
    Hall, Josefine
    Högskolan Dalarna, Akademin Industri och samhälle, Materialteknik.
    Svensson, J. -E
    Johansson, L. G.
    Liske, J.
    The effect of H2 and H2O on the oxidation of 304L-stainless steel at 600 °C: general behaviour (part I)2016Ingår i: Oxidation of Metals, ISSN 0030-770X, E-ISSN 1573-4889, Vol. 85, nr 3-4, s. 321-342Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The effect of p(H2O) and p(H2) on the oxidation of 304L stainless steel at 600 °C has been investigated in the present study. The samples were analysed by means of X-ray diffraction, Auger spectroscopy, and scanning electron microscopy equipped with energy dispersive spectroscopy. The results showed that at fixed p(H2), the corrosion rate increased considerably with increasing p(H2O). At fixed p(H2O), the corrosion rate decreased slightly with increasing p(H2). Duplex oxide scales formed during the exposure in all environments. The outer and inner layer consisted of Fe3O4 and (Fe, Cr)3O4, respectively. The latter was mainly in the form of internal oxidation. The Cr-rich oxide formation was observed at the initial oxidation process before oxide breakdown. The Auger analysis also suggested the presence of Cr-rich oxide layer just after the breakaway oxidation. The results indicated that the rate-determining step in the corrosion attack is surface controlled or diffusion controlled through an oxide layer with fixed thickness over time.

  • 104.
    Huang, Shuo
    et al.
    Royal Inst Technol, Dept Mat Sci & Engn, Appl Mat Phys, SE-10044 Stockholm, Sweden..
    Vida, Adam
    Wigner Res Ctr Phys, Inst Solid State Phys & Opt, POB 49, H-1525 Budapest, Hungary.;Eotvos Lorand Univ, Dept Mat Phys, Pazmany Peter Setany 1-A, H-1117 Budapest, Hungary..
    Li, Wei
    Royal Inst Technol, Dept Mat Sci & Engn, Appl Mat Phys, SE-10044 Stockholm, Sweden..
    Molnar, David
    Högskolan Dalarna, Akademin Industri och samhälle, Materialteknik. KTH.
    Kwon, Se Kyun
    Pohang Univ Sci & Technol, Grad Inst Ferrous Technol, Pohang 37673, South Korea..
    Holmstrom, Erik
    Sandvik Coromant R&D, S-12680 Stockholm, Sweden..
    Varga, Bela
    Transylvania Univ Brasov, Fac Mat Sci, Bulevardul Eroilor 29, Brasov 500036, Romania..
    Varga, Lajos Karoly
    Wigner Res Ctr Phys, Inst Solid State Phys & Opt, POB 49, H-1525 Budapest, Hungary..
    Vitos, Levente
    Royal Inst Technol, Dept Mat Sci & Engn, Appl Mat Phys, SE-10044 Stockholm, Sweden.;Wigner Res Ctr Phys, Inst Solid State Phys & Opt, POB 49, H-1525 Budapest, Hungary.;Uppsala Univ, Div Mat Theory, Dept Phys & Astron, Box 516, SE-75120 Uppsala, Sweden..
    Thermal expansion in FeCrCoNiGa high-entropy alloy from theory and experiment2017Ingår i: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 110, nr 24, artikel-id 241902Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    First-principle alloy theory and key experimental techniques are applied to determine the thermal expansion of FeCrCoNiGa high-entropy alloy. The magnetic transition, observed at 649 K, is accompanied by a significant increase in the thermal expansion coefficient. The phase stability is analyzed as a function of temperature via the calculated free energies accounting for the structural, magnetic, electronic, vibrational and configurational contributions. The single-and polycrystal elastic modulus for the ferro-and paramagnetic states of the face-centered and body-centered cubic phases are presented. By combining the measured and theoretically predicted temperature-dependent lattice parameters, we reveal the structural and magnetic origin of the observed anomalous thermal expansion behavior. Published by AIP Publishing.

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  • 105. Hultquist, G.
    et al.
    Graham, M. J.
    Kodra, O.
    Moisa, S.
    Liu, R.
    Bexell, Ulf
    Högskolan Dalarna, Akademin Industri och samhälle, Materialteknik.
    Smialek, J. L.
    Corrosion of copper in distilled water without O-2 and the detection of produced hydrogen2015Ingår i: Corrosion Science, ISSN 0010-938X, E-ISSN 1879-0496, Vol. 95, s. 162-167Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    This paper reports on hydrogen pressures measured during similar to 19,000 h immersion of copper in oxygen-free liquid distilled water. Copper corrosion products have been examined ex-situ by SEM and characterized by XPS and SIMS. XPS strongly indicates a corrosion product containing both oxygen and hydrogen. SIMS shows that oxygen is mainly present in the outer 0.3 mu m surface region and that hydrogen penetrates to depths well below the corrosion product. Thermal desorption spectroscopy shows that the reaction product formed near room-temperature is less stable than that formed in air at 350 degrees C. 

  • 106. Hörnström, S. -E
    et al.
    Karlsson, E.
    Losch, A.
    Olsson, Mikael
    Högskolan Dalarna, Akademin Industri och samhälle, Materialteknik.
    Bay, N.
    Forming of high-strength steels using a hot-melt dry lubricant2010Ingår i: 17th International Colloquium Tribology 2010 - Solving Friction and Wear Problems, 2010, Vol. 2, s. 958-971Konferensbidrag (Refereegranskat)
    Abstract [en]

    The increasing use of high strength steels in a variety of mechanical engineering applications has illuminated problems associated with galling in sheet metal forming operations. Galling is a tribological phenomenon associated with transfer of material from the steel sheet to the tool surface during forming resulting in seizure of the tool/steel sheet contact and extensive scratching of the steel sheet surface. As a result, a number of concepts have been developed in order to reduce the tendency to galling in metal forming, including the development of new dry lubricants, new forming tool steel grades and improved surface engineering treatments such as the deposition of low friction CVD and PVD coatings. In the present study the performance of a hot-melt dry lubricant in the forming of hot and cold rolled and hot-dip galvanized high strength steel has been evaluated and compared with a conventional rust protection oil using five different tests methods, i.e. a strip reduction test, a bending under tension test, a stretch-forming test, a pin-on disc test and a strip drawing test. In these tests, two different cold work tool steels, a conventional steel grade and a nitrogen alloyed PM steel grade were evaluated. The results show that the different tests used give consistent results and valuable information concerning the galling tendency of the steel sheet, tool steel and lubricant combinations investigated and when combined can be used to rank the galling resistance of lubricants and tool steels. The results clearly show that the dry lubricant provides better lubrication and generates less galling than the rust protection oil. Also, the nitrogen alloyed PM steel grade shows a significantly higher galling resistance as compared with the conventional steel grade and can, in combination with a dry lubricant, preferably be used in sheet metal forming operations to further improve the galling resistance.

  • 107. Ingemarsson, L.
    et al.
    Halvarsson, M.
    Engkvist, Josefin
    Högskolan Dalarna, Akademin Industri och samhälle, Materialvetenskap.
    Jonsson, T.
    Hellstrom, K.
    Johansson, L. -G
    Svensson, J. -E
    Oxidation behavior of a Mo (Si, Al)(2)-based composite at 300-1000 degrees C2010Ingår i: Intermetallics (Barking), ISSN 0966-9795, E-ISSN 1879-0216, Vol. 18, nr 4, s. 633-640Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The oxidation behavior of a Mo (Si,Al)(2)-based composite of Mo(Si,Al)(2), Al2O3 and Mo-5(Si,Al)(3) (Kanthal Super ER) in synthetic air was investigated. The samples were oxidized isothermally for up to 72 h at 300-1000 degrees C using a thermobalance. The microstructure was analyzed by X-ray diffraction (XRD), Scanning Electron Microscopy (SEM) and Auger Electron Spectroscopy (AES) depth profiling. Broad ion beam milling (BIB) was used to prepare cross-sections. Oxidation behavior depended strongly on the composition of the substrate which consisted of a Mo(Si,Al)(2) matrix and the minority phases Mo-5(Si,Al)(3) and Al2O3. At 300-500 degrees C the mass gains were small with parabolic kinetics, oxidation resulting in a mixture of oxides that reflects the substrate composition. At 600 and 700 degrees C the oxide scale is thin and protective and depleted in molybdenum, a mass loss occurring due to MoO3 vaporization. At 1000 degrees C a protective alpha-alumina scale forms. (C) 2009 Elsevier Ltd. All rights reserved.

  • 108.
    Isgren, Peter
    Högskolan Dalarna, Akademin Industri och samhälle, Materialteknik.
    Dragprovstavens geometripåverkan på mätresultatet2015Självständigt arbete på grundnivå (kandidatexamen), 10 poäng / 15 hpStudentuppsats (Examensarbete)
    Abstract [sv]

    Examensarbetet bygger på en jämförelse av standard SS 112113 med en geometri som kan beskrivas som rak och standard SS-EN 1561:2011 som kan beskrivas som timglasformad för dragprovning. Undersökningen ska ge djupare förståelse för vilken effekt olika dragprovsgeometrier och dragprovshastigheter har på brottgränsen och dess spridning. Syftet är att finna en lämplig geometri och draghastighet som ger liten spridning samt att koppla mikrostruktur till mätresultatet. Sjuttio dragprov ingår i studien och dessa är gjutna från samma gråjärnssmälta i likadana sandformar. De svarvade provstavarna är dragprovade i en Zwick dragprovmaskin. Ljusmikroskop har använts för att undersöka defekter i brottytan, grovlek på ytan samt för grafitklassificering. Svepelektronmikroskop har använts för att kontrollera rost på dragprovsytan. Hårdhetsmätning enligt Brinell är utförd på utvalda prov då det finns ett samband mellan hållfasthet och hårdhet. Brottgränsen är lägre och spridningen är mindre för standard SS 112113 än för standard SS-EN 1561:2011. Brottet inträffar på varierade positioner för standard SS 112113 och för standard SS-EN 1561:2011 sker brott i den tunna sektionen där spänningen blir störst. Varierad draghastighet ger inte någon signifikant skillnad i brottgräns eller spridning. Mikrostrukturen med avseende på grafittyp, grafitlängd förklarar inte skillnaden i brottgräns eller spridning.

  • 109.
    Ismail, Kasimagwa
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad processmetallurgi.
    Brabie, Voicu
    The use of thermodynamic computations to predict the phase transformation in MgO-C refractories during steel refining2008Ingår i: Refractories Manual, s. 42-47Artikel i tidskrift (Refereegranskat)
  • 110.
    Jacobson, S
    et al.
    Uppsala Universitet.
    Beste, U
    Uppsala Universitet.
    Heinrichs, J
    Uppsala Universitet.
    Olsson, Mikael
    Högskolan Dalarna, Akademin Industri och samhälle, Materialteknik.
    Wiklund, U
    Uppsala Universitet.
    On the nature of cemented carbide wear in rock drilling2014Ingår i: Hard Rock Tribology Course and Seminar, Tampere, Finland, November 4-5, 2014, 2014Konferensbidrag (Övrigt vetenskapligt)
  • 111. Jansson, S.
    et al.
    Brabie, Voicu
    Högskolan Dalarna, Akademin Industri och samhälle, Materialteknik.
    Jonsson, P.
    Magnesia-carbon refractory dissolution in Al killed low carbon steel2006Ingår i: Ironmaking & steelmaking, ISSN 0301-9233, E-ISSN 1743-2812, Vol. 33, nr 5, s. 389-397Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The effects of rotation speed, steel temperature and steel composition on the rate of dissolution of MgO-C refractory into Al deoxidised molten steel were investigated using the rotating cylinder method. Cylinders or rods of MgO-C refractory material were immersed in an Al deoxidised molten steel. Experiments were performed for steel temperatures between 1873 and 1973 K and rotation speeds between 100 and 800 rev min(-1) as well as for different immersion times. For each case, the dissolution rate of MgO-C material was determined from measurement of the decrease in the rod radius. The experimental results showed that the dissolution rate of the MgO-C refractory material increased with an increase in steel temperature and rotation speed. The findings strongly suggest the diffusion of magnesium through the slag layer formed around the refractory rods to be a rate determining step. This thin oxide layer at the steel/refractory interface was found to be owing to reaction between magnesium vapour and CO generated by the reaction between MgO and C in the refractory. Oxide inclusions were also found in the steel melt and they were shown to mainly consist of MgO and Al2O3 or a mixture of the two.

  • 112. Jansson, Sune
    et al.
    Brabie, Voicu
    Högskolan Dalarna, Akademin Industri och samhälle, Materialteknik.
    Jonsson, P.
    Corrosion mechanism of commercial doloma refractories in contact with CaO-Al2O3-SiO2-MgO stag2008Ingår i: Ironmaking & steelmaking, ISSN 0301-9233, E-ISSN 1743-2812, Vol. 35, nr 2, s. 99-107Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The dissolution of three doloma based refractories in liquid CaO-Al2O3-SiO2-MgO slag was studied. Cylindrical refractory specimens of doloma, carbon bonded doloma, and magnesia doloma were rotated in a stationary crucible of molten slag under forced convection conditions. Slag composition, temperature, rod rotation speed and rod immersion time were varied. The refractory dissolution rate was determined from the change in diameter of the cylindrical specimens. The corrosion rate was found to increase with temperature and rod rotation speed and decrease when the slag was nearly saturated with MgO. The findings of the study substantiate the assumption that the diffusion of magnesium oxide through the slag boundary layer controls the corrosion process. The results indicated the overall corrosion process to be the dissolution of refractory material into the slag, followed by slag penetration of the pores and grain boundaries and finally, dispersion of the grains into the slag.

  • 113. Jansson, Sune
    et al.
    Brabie, Voicu
    Högskolan Dalarna, Akademin Industri och samhälle, Materialteknik.
    Josson, Par
    Corrosion mechanism of commercial MgO-C refractories in contact with different gas atmospheres2008Ingår i: ISIJ International, ISSN 0915-1559, E-ISSN 1347-5460, Vol. 48, nr 6, s. 760-767Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Corrosion of MgO-C refractories in different gas atmospheres consisting of air, Ar, CO or Ar/CO was studied in laboratory experiments. In total, 103 experiments were carried out in the temperature range 1 173 to 1 773 K and for holding times between 2 to 120 min. The reaction rate of the MgO-C material was determined from measurements of the weight loss of the samples. The results showed that the refractory weight loss increased with an increased temperature or an increased holding time. The thermodynamic conditions and the experimental results showed that magnesium gas and carbon monoxide gas should form during ladle refining of steel when the refractory material consists of MgO-C. It was suggested that the reaction rate is directly dependent on the oxygen potential in the ambient atmosphere.

  • 114. Jansson, Sune
    et al.
    Brabie, Voicu
    Högskolan Dalarna, Akademin Industri och samhälle, Materialteknik.
    Jönsson, Pär
    Corrosion mechanism and kinetic behaviour of MgO-C refractory material in contact with CaO-Al2O3-SiO2-MgO slag2005Ingår i: Scandinavian journal of metallurgy, ISSN 0371-0459, E-ISSN 1600-0692, Vol. 34, nr 5, s. 283-292Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The rate of dissolution of solid MgO-C into liquid CaO-Al2O3-SiO2-MgO slag at different temperatures was studied under conditions of forced convection by rotating cylindrical refractory specimens in a stationary crucible containing molten slag. The corrosion rate was calculated from the change in diameter of the cylindrical refractory specimens. The specimens were rotated for 15-120 min at a speed of 100-400 rpm in the molten slag. The rate of corrosion was found to increase with an increase in temperature and rod rotation speed, and to decrease when the slag was nearly saturated with MgO. The experimental results support the assumption that the diffusion of magnesium oxide through the slag-phase boundary layer controls the corrosion process. The corrosion mechanism seems to be the dissolution of refractory material into the slag followed by penetration of pores and grain boundaries and dispersion of the grains into the slag.

  • 115. Jayamani, Jayaraj
    et al.
    Fleury, E.
    Park, B. J.
    Kim, D. H.
    Kim, W. T.
    Synthesis and characterization of nanometer-sized Ti-based amorphous powders2007Ingår i: Journal of Materials Research, ISSN 0884-2914, E-ISSN 2044-5326, Vol. 22, nr 6Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We present a simple method for preparing nanometer-sized, Ti-based amorphous powders from the Y28Ti28Al24Co20and Y36Ti20Al24Co20two-phase amorphous alloys. The initial microstructure of these rapidly quenched alloys is composed of Ti-based, amorphous, spherical, nanometer-sized particles embedded in a Y-based amorphous matrix, with particle size dependent on the alloy composition. The Ti-based powders were extracted from the two-phase amorphous alloys through selective dissolution of the Y-rich matrix in a 0.1 M HNO3solution. The powders of size ranging between 20 and 200 nm have smooth and spherical morphology, and exhibit different magnetic behavior than the bulk alloy of identical composition.

  • 116. Jayamani, Jayaraj
    et al.
    Fleury, Eric
    Kim, Ki-Bae
    Lee, Jae-Chul
    Globulization mechanism of the primary Al of Al−15Cu alloy during slurry preparation for rheoforming2005Ingår i: Metals and Materials International, ISSN 1598-9623, E-ISSN 2005-4149, Vol. 11, nr 3Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Semisolid slurries of Al-15Cu alloy were produced for rheoforming by a low temperature pouring technique. To investigate the morphological change of the slurry in terms of the particle mean diameter and the roundness factor, samples were extracted during the continuous cooling and the isothermal holding stage of the slurry by a simple technique of interrupt quenching. Results demonstrated that the fine-grained equiaxed dendritic structure, which formed during low temperature pouring, is changed to a globular structure when held at a semisolid temperature for sufficiently long holding time. With regard to the globulization mechanism of the primary α-phase, local melting is considered to take place at the neck of equiaxed dendrites, leading to the separation of small new particles during continuous cooling. These newly formed particles eventually grow during isothermal holding in the semisolid temperature by obeying theD3=Kt kinetic law, which suggests coarsening by Ostwald ripening.

  • 117. Jayamani, Jayaraj
    et al.
    Gebert, A.
    Schultz, L.
    Passivation behaviour of structurally relaxed Zr48Cu36Ag8Al8 metallic glass2009Ingår i: Journal of Alloys and Compounds, ISSN 0925-8388, E-ISSN 1873-4669, Vol. 479, nr 1, s. 257-261Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The electrochemical corrosion behaviour of as-prepared and structurally relaxed Zr48Cu36Ag8Al8 glassy alloy samples was investigated in 1M H2SO4. Results show that the active–passive transition behaviour of Zr48Cu36Ag8Al8 glassy alloy depends on the amount of free volume (FV) present in the metallic glassy alloy. Poor passivation due to active dissolution of Cu was displayed by the Zr48Cu36Ag8Al8 glassy alloy when it was in a high energy metastable state with relative high amount of FV. It is shown that by reducing the amount of FV in the glass, the passivation behaviour is significantly improved.

  • 118.
    Jayamani, Jayaraj
    et al.
    Korea Institute of Science and Technology, South Korea.
    Han, Jae Ho
    Park, Sang Whan
    Kim, Ki Bae
    Fleury, Eric
    Potential of Cr2AlC Ternary Carbide as Material for Bipolar Plate in PEMFC2007Ingår i: Solid State Phenomena, ISSN 1012-0394, E-ISSN 1662-9779, Vol. 124-126, s. 927-930Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    In this paper, we present results of an investigation on the physical, mechanical, chemical properties and processing ability of the Cr2AlC ternary carbide bulk material synthesized by hot pressing technique. The combination of excellent properties indicated that Cr2AlC ternary carbide alloy could be potential candidate materials as bipolar plates in polymer membrane fuel cell (PEMFC).

  • 119. Jayamani, Jayaraj
    et al.
    Kim, K. B.
    Ahn, H. S.
    Fleury, E.
    Corrosion mechanism of N-containing Fe–Cr–Mo–Y–C–B bulk amorphous alloys in highly concentrated HCl solution2007Ingår i: Materials Science & Engineering: A, ISSN 0921-5093, E-ISSN 1873-4936, Vol. 449-451, s. 517-520Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The Fe49Cr15.3Mo15Y2C15B3.4N0.3 (numbers indicate at.%) amorphous alloy in concentrated HCl solution was found to have a corrosion resistance of at least one order of magnitude higher than the N-free Fe-base amorphous alloy. X-ray photoelectron spectroscopy analyses were performed to understand the corrosion mechanism. It was found that the enrichment of Cr oxide and the presence of MoN nitrides on the surface in the passive layer were at the origin of the high corrosion resistance of the N-containing Fe-base amorphous alloy.

  • 120. Jayamani, Jayaraj
    et al.
    Kim, Y. C.
    Kim, K. B.
    Seok, H. K.
    Fleury, E.
    Corrosion behaviors of Fe45−xCr18Mo14C15B6Y2Mx (M=Al, Co, Ni, N and x=0, 2) bulk metallic glasses under conditions simulating fuel cell environment2007Ingår i: Journal of Alloys and Compounds, ISSN 0925-8388, E-ISSN 1873-4669, Vol. 434-435, s. 237-239Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The corrosion properties of the Fe45−xCr18Mo14C15B6Y2Mx (with M=Al, Co, Ni, N and x=0, 2) bulk metallic glasses have been investigated in a 1M H2SO4+2ppm F− solution at 80°C with H2 and air bubbling, which simulate environments of the polymer electrolyte membrane fuel cell. The partial replacement of 2at.% Fe led to significant modification of the corrosion behavior and resulted in corrosion resistances superior to that of stainless steel.

  • 121. Jayamani, Jayaraj
    et al.
    Kim, Y. C.
    Kim, K. B.
    Seok, H. K.
    Fleury, E.
    Corrosion studies on Fe-based amorphous alloys in simulated PEM fuel cell environment2005Ingår i: Science and Technology of Advanced Materials, ISSN 1468-6996, E-ISSN 1878-5514, Vol. 6, nr 3-4, s. 282-289Artikel i tidskrift (Refereegranskat)
  • 122. Jayamani, Jayaraj
    et al.
    Kim, Y. C.
    Seok, H. K.
    Kim, K. B.
    Fleury, E.
    Development of metallic glasses for bipolar plate application2007Ingår i: Materials Science & Engineering: A, ISSN 0921-5093, E-ISSN 1873-4936, Vol. 449-451, s. 30-33Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Fe- and Ni-base amorphous alloys were developed and characterized as alternative bipolar plate materials for polymer electrolyte membrane fuel cell (PEMFC). Lower interfacial contact resistances were obtained for the Fe-base in comparison with Ni-base alloys and particularly the N-containing Fe-base amorphous composition exhibited values almost comparable to that of stainless steel upon high compaction load. Under conditions simulating the anodic and cathodic PEMFC environments, both the Fe- and Ni-base amorphous alloys displayed higher corrosion resistance than stainless steel.

  • 123. Jayamani, Jayaraj
    et al.
    Krishnaveni, P.
    Krishna, D. Nanda Gopala
    Mallika, C.
    Mudali, U. Kamachi
    Corrosion investigations on zircaloy-4 and titanium dissolver materials for MOX fuel dissolution in concentrated nitric acid containing fluoride ions2016Ingår i: Journal of Nuclear Materials, ISSN 0022-3115, E-ISSN 1873-4820, Vol. 473, s. 157-166Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Aqueous reprocessing of plutonium-rich mixed oxide fuels require fluoride as a dissolution catalyst in boiling nitric acid for an effective dissolution of the spent fuel. High corrosion rates were obtained for the candidate dissolver materials zircaloy-4 (Zr-4) and commercial pure titanium (CP-Ti grade 2) in boiling 11.5 M HNO3 + 0.05 M NaF. Complexing the fluoride ions either with Al(NO3)3 or ZrO(NO3)2 aided in decreasing the corrosion rates of Zr-4 and CP-Ti. From the obtained corrosion rates it is concluded that CP-Ti is a better dissolver material than Zr-4 for extended service life in boiling 11.5 M HNO3+0.05 M NaF, when complexed with 0.15 M ZrO(NO3)2. XPS analysis confirmed the presence of TiO2 and absence of fluoride on the surface of CP-Ti samples, indicating that effective complexation had occurred in solution leading to passivation of the metal and imparting high corrosion resistance.

  • 124. Jayamani, Jayaraj
    et al.
    Mendis, C. L.
    Ohkubo, T.
    Oh-ishi, K.
    Hono, K.
    Enhanced precipitation hardening of Mg–Ca alloy by Al addition2010Ingår i: Scripta Materialia, ISSN 1359-6462, E-ISSN 1872-8456, Vol. 63, nr 8, s. 831-834Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We report the enhanced precipitation-hardening response of Mg–0.5Ca (wt.%) alloy by microalloying with Al. The peak hardness of 50 HV for the binary alloy was enhanced to 72 HV in a ternary Mg–0.5Ca–0.3Al alloy. Transmission electron microscopy and 3D atom probe analyses confirmed that the improvement in the peak hardness is associated with the dense precipitation of ordered monolayer Guinier–Preston zones and the subsequent formation of Al2Ca causes the over-aging.

  • 125. Jayamani, Jayaraj
    et al.
    Mudali, U. Kamachi
    Electrochemical Activity at the Interface of Dissimilar Explosive Joint of Stainless Steel with Zircaloy by Scanning Electrochemical Microscopy2012Ingår i: Journal of Advanced Microscopy Research, ISSN 2156-7573, E-ISSN 2156-7581, Vol. 7, nr 3, s. 214-217Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Electrochemical activity at the interface of dissimilar explosive joint of stainless steel with Zircaloy has been studied in 11.5 M nitric acid using scanning electrochemical microscopy. The reduction of nitric acid and oxidation of nitrous acid in the tip-substrate gap is proposed as a mechanism for the electron transfer reaction. Due to this reaction increase in tip current was observed, indicating that the positive feedback mode of SECM is under operation. The difference in tip current was correlated with the microstructure and the electrochemical activity of the dissimilar weld interface.

  • 126. Jayamani, Jayaraj
    et al.
    Nanda Gopala Krishna, D.
    Mallika, C.
    Kamachi Mudali, U.
    Electrochemical Studies and XPS Analysis of the Surface of Zirconium-702 in Concentrated Nitric Acid With and Without Fluoride Ions2018Ingår i: Transactions of the Indian Institute of Metals, ISSN 0972-2815, E-ISSN 0975-1645, Vol. 71, nr 3, s. 521-531Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Zirconium exhibited pseudo-passive behavior in fluorinated nitric acid (11.5 M HNO3 + 0.05 M NaF) as the current density measured from the electrochemical studies was several orders higher than the value in fluoride free nitric acid. Impedance studies on zirconium sample exposed in 11.5 M HNO3 for 240 h confirmed the formation of the passive film with high polarization resistance value and the calculated thickness of the film based on the capacitance value was about ~4.5 nm. On the other hand, in fluorinated nitric acid, the charge transfer resistance value associated with the zirconium dissolution process was dominant when compared to that of the film formation. Results of X-ray photoelectron spectroscopic investigations upheld the presence of ZrOF2 and ZrF4 and indicated that the protective oxide layer growth was restricted by the presence of fluoride ions.

  • 127. Jayamani, Jayaraj
    et al.
    Nanda Gopala Krishna, D.
    Mallika, C.
    Kamachi Mudali, U.
    Passive film properties and corrosion behavior of Ni–Nb and Ni–Nb–Ta amorphous ribbons in nitric acid and fluorinated nitric acid environments2015Ingår i: Materials Chemistry and Physics, ISSN 0254-0584, E-ISSN 1879-3312, Vol. 151, s. 318-329Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Potentiodynamic polarization and electrochemical impedance studies revealed the passivation ability and corrosion resistance of Ni60Nb40 and Ni60Nb30Ta10 amorphous ribbons in 11.5 M HNO3 and 11.5 M HNO3 + 0.05 M NaF media at room temperature. Mott–Schottky analysis indicated the formation of n-type semiconducting passive film on these amorphous ribbon samples. Electrochemical parameters such as corrosion current density, passivation current density and donor density confirmed the passive film property of Ni60Nb30Ta10 amorphous ribbon to be superior to that of Ni60Nb40 amorphous ribbon. Weight loss was insignificant in Ni60Nb30Ta10 ribbon exposed to boiling 11.5 M HNO3 for 240 h. XPS analysis revealed that the origin of passivity of Ni60Nb40 and Ni60Nb30Ta10 amorphous ribbons in boiling 11.5 M HNO3 was due to the formation of a relatively thick passive film of ≈3 nm enriched with Nb2O5 and a thin passive film of ≈1.5 nm enriched with both Nb2O5 and Ta2O5 on the respective ribbon's surface. In boiling fluorinated nitric acid, Ni60Nb40 ribbon underwent severe dissolution owing to the instability of Nb-oxide passive film and the oxide/metal interface.

  • 128. Jayamani, Jayaraj
    et al.
    Park, B. J.
    Kim, D. H.
    Kim, W. T.
    Fleury, E.
    Nanometer-sized porous Ti-based metallic glass2006Ingår i: Scripta Materialia, ISSN 1359-6462, E-ISSN 1872-8456, Vol. 55, nr 11, s. 1063-1066Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    A porous Ti-based metallic glass has been fabricated by applying the principle of dealloying to the Y20Ti36Al24Co20 two-phase amorphous alloy. The initial microstructure of the two-phase glassy alloy consisted of Ti43.3Y3.7Al15.3Co37.7 and Y38.8Ti12.8Al37.1Co11.3 amorphous phases forming an interconnected structure. To fabricate the porous structure, the Y-rich phase has been selectively dissolved from the alloy using both chemical and electrochemical treatments in 0.1M HNO3 solution. The glassy nature of the porous Ti-based alloy was confirmed by transmission electron microscopy analyses.

  • 129. Jayamani, Jayaraj
    et al.
    Park, J. M.
    Gostin, P. F.
    Fleury, E.
    Gebert, A.
    Schultz, L.
    Nano-porous surface states of Ti–Y–Al–Co phase separated metallic glass2009Ingår i: Intermetallics (Barking), ISSN 0966-9795, E-ISSN 1879-0216, Vol. 17, nr 12, s. 1120-1123Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    A novel nano-porous state was fabricated at the surface of the Ti-based metallic glass by selective etching technique. By transforming the surface of the Ti45Y11Al24Co20 phase separated alloy from smooth towards rough with nano-pores in an oxidised state, the passivation behaviour of the glassy alloy in simulated body fluid condition was remarkably improved leading to corrosion resistance significantly higher than that of the Ti–6Al–4V alloy, one of the favourite candidate materials for implant applications.

  • 130. Jayamani, Jayaraj
    et al.
    Ranjith, P. M.
    Ningshen, S.
    Ramanathan, S.
    Studies on Corrosion of Titanium and Air-Oxidized Titanium in Fluorinated Nitric Acid2019Ingår i: Transactions of the Indian Institute of Metals, ISSN 0972-2815, E-ISSN 0975-1645, Vol. 72, nr 7, s. 1917-1926Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Titanium (Ti) is a lustrous transition metal which possesses excellent corrosion resistance in several aggressive environments but is attacked by acidic fluoride media. In this work, the addition of fluoride ion to nitric acid on the corrosion behavior of Ti and air-oxidized Ti was studied. Air oxidation of Ti at 800 °C for 5 h resulted in the formation of an intact rutile TiO2 layer with a thickness of about 35 μm. The corrosion resistance was investigated from the polarization resistance ($$R_{\text{P}}$$RP) values which were obtained from linear polarization and electrochemical impedance spectroscopy (EIS) measurements. A decrease in the $$R_{\text{P}}$$RPvalue of Ti with the addition of fluoride ion in nitric acid was observed, and this indicated the formation of an unstable layer, which resulted in accelerated dissolution. The several order increase in the $$R_{\text{P}}$$RPvalue of air-oxidized Ti in nitric acid containing fluoride ions pointed the improved resistance to corrosion. The diffusivity of species through the air-oxidized TiO2 layer was estimated from the electrochemical equivalent circuit (EEC) analysis of EIS data. Even though the diffusivity increased by several orders with the addition of fluoride ions, air-oxidized Ti provided better protection against nitric acid containing fluoride ions than Ti. The corrosion rates of Ti and air-oxidized Ti in boiling nitric acid containing fluoride ions were also estimated from weight loss experiments. Even in boiling fluorinated nitric acid, air-oxidized Ti provided better corrosion protection, with corrosion rates of about 1000 times less than that of Ti.

  • 131. Jayamani, Jayaraj
    et al.
    Ravi, K. R.
    Mallika, C.
    Kamachi Mudali, U.
    Microstructure and Corrosion Behavior of Hf-40 Wt Pct Ti Alloy in Nitric Acid Medium for Reprocessing Applications2016Ingår i: Metallurgical and Materials Transactions. A, ISSN 1073-5623, E-ISSN 1543-1940, Vol. 47, nr 9, s. 4393-4403Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The Hf-40 wt pct Ti (Hf-Ti) alloy was developed for neutron poison application in the spent nuclear fuel reprocessing plant. The furnace-cooled Hf-Ti sample exhibited the microstructure comprising equiaxed-α, lamellar-α, and feathery-α. The water-quenched Hf-Ti sample confirmed the presence of lath and internally twinned martensite. In comparison to the furnace-cooled sample, low corrosion current density and passivation current density values obtained for the water-quenched Hf-Ti in 6 M HNO3 at 298 K (25 °C) indicated better passivation ability. The martensitic structure exhibited high hardness (660 HV) and negligible corrosion rate in 6 M nitric acid at 298 K (25 °C). X-ray photoelectron spectroscopic (XPS) analysis confirmed that passivation behavior of this alloy was due to the protective passive film composed of TiO2 and HfO2.

  • 132. Jayamani, Jayaraj
    et al.
    Ravi Shankar, A.
    Kamachi Mudali, U.
    Electrochemical and passive characterization of a beta type Ti45Zr38Al17 cast rod in nitric acid medium2012Ingår i: Electrochimica Acta, ISSN 0013-4686, E-ISSN 1873-3859, Vol. 85, s. 210-219Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Electrochemical behavior of the recently developed beta-type Ti–38at% Zr–17at% Al (TZA) alloy has been studied in nitric acid medium for applications in nuclear reprocessing plant. Potentiodynamic polarization and electrochemical impedance studies revealed that the passive film formed on the TZA alloy was highly protective in nature. Mott–Schottky analysis of the passive film formed on TZA alloy showed n-type semiconducting properties. The electrochemical data confirmed the superior corrosion resistance of TZA alloy as the passive film formed exhibited better properties than that of the commercial pure Ti. XPS analyses confirmed that the stable passivity of TZA alloy in nitric acid was due to the formation of thick and protective passive layer, predominantly of ZrO2 with TiO2.

  • 133. Jayamani, Jayaraj
    et al.
    Sordelet, D. J.
    Kim, D. H.
    Kim, Y. C.
    Fleury, E.
    Corrosion behaviour of Ni–Zr–Ti–Si–Sn amorphous plasma spray coating2006Ingår i: Corrosion Science, ISSN 0010-938X, E-ISSN 1879-0496, Vol. 48, nr 4, s. 950-964Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Ni59Zr20Ti16Si2Sn3 amorphous material was deposited by a vacuum plasma spraying technique onto steel and copper substrates in order to investigate their behaviour in a corrosive environment. For comparison, the same alloy was prepared as amorphous ribbons by melt spinning. The amorphous nature of the coatings and ribbons was characterized by XRD, DSC and TEM, while XPS and AES analyses were performed to understand the origin of passivation and mode of corrosion. The corrosion behaviour of the coating was studied in H2SO4 and HCl solutions open to air at room temperature. Potentiodynamic polarisation and galvanic coupling tests were carried out on the substrate and the coating. It was found that the formation of Zr-, Ti- and Si-rich passive oxide layers provide a high corrosion resistance in H2SO4 solution while the breakdown of the passive layer by chloride ion adsorption was responsible for pitting corrosion of the Ni59Zr20Ti16Si2Sn3 amorphous ribbons in HCl solution. Galvanic corrosion was the dominant corrosion mechanism for the coating/copper hybrid structure, in contrast to the Ni59Zr20Ti16Si2Sn3 amorphous coating, which efficiently protected the steel substrate in the corrosive environment.

  • 134. Jayamani, Jayaraj
    et al.
    Thinaharan, C.
    Ningshen, S.
    Mallika, C.
    Kamachi Mudali, U.
    Corrosion behavior and surface film characterization of TaNbHfZrTi high entropy alloy in aggressive nitric acid medium2017Ingår i: Intermetallics (Barking), ISSN 0966-9795, E-ISSN 1879-0216, Vol. 89, s. 123-132Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Corrosion behavior of TaNbHfZrTi high-entropy alloy (HEA) was investigated in nitric and fluorinated nitric acid at ambient (27 °C) and boiling (120 °C) conditions. The alloy passivated spontaneously during potentiodynamic polarization in 11.5 M HNO3 at ambient condition. The corrosion rate was negligible in boiling 11.5 M HNO3, exposed for 240 h. Scanning electron microscopic (SEM) studies did not show any significant corrosion attack. The high corrosion resistance of TaNbHfZrTi HEA was attributed to its single phase bcc structure. X-ray photoelectron spectroscopic (XPS) analysis revealed that the protective passive film formed in boiling nitric acid was predominantly composed of Ta2O5, in contrast to the presence of ZrO2 and HfO2 in air-formed native film. Potentiodynamic polarization studies indicated a pseudo-passivation behavior of the HEA in 11.5 M HNO3 + 0.05 M NaF at ambient condition. In boiling fluorinated nitric acid, SEM images of TaNbHfZrTi HEA displayed a severely corroded morphology indicating the instability of the metal-oxides of the alloying elements. XPS investigations confirmed the presence of ZrF4, ZrOF2 and HfF4 along with un-protective oxides of Ta, Nb and Ti on the film, resulting in decreased corrosion resistance of TaNbHfZrTi HEA in fluorinated nitric acid.

  • 135. Jayamani, Jayaraj
    et al.
    Thirathipviwat, Pramote
    Han, Junhee
    Gebert, Annett
    Microstructure, mechanical and thermal oxidation behavior of AlNbTiZr high entropy alloy2018Ingår i: Intermetallics (Barking), ISSN 0966-9795, E-ISSN 1879-0216, Vol. 100, s. 9-19Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The developed as-cast AlNbTiZr high entropy alloy (HEA) resulted in the formation of solid solution bcc dendrites along with the inter-dendritic Zr2Al intermetallic phase. Due to low-density of 5.74 g/cm3 and high yield strength of about 1650 MPa (under compression testing), the alloy exhibited high specific yield strength of approximately 287 kPa m3/kg. Further, the AlNbTiZr HEA showed high fracture strength of 1950 MPa and substantial plastic strain of approximately 17.9%. During the isothermal thermo-gravimetry analysis in the synthetic air, at 873, 973, 1073, 1173 and 1273 K for 3 h, the mass gain behavior of the alloy was nearly parabolic indicating the formation of the protective oxide layer. Further, the long-term oxidation studies of the AlNbTiZr HEA carried out in open air atmosphere for 50 h at 873, 1073 and 1273 K confirmed that the oxide layers formed were protective, intact, and spallation did not occur. Formation of complex oxides such as AlNbO4 and Ti2ZrO6 along with Al2O3, NbO, ZrO2, and TiO2 as confirmed by X-ray diffraction could have led to the sluggish oxidation kinetics of the AlNbTiZr HEA. In contrast, the HfNbTiZr HEA showed poor oxidation resistance at 873 K.

  • 136. Jayamani, Jayaraj
    et al.
    Thyagarajan, K.
    Mallika, C.
    Mudali, U. Kamachi
    Corrosion Behavior of Zirconium, Titanium, and Their Alloys in Simulated Dissolver Solution of Fast Breeder Reactor Spent Nuclear Fuel Using Zircaloy-4 Mock-Up Dissolver Vessel2015Ingår i: Nuclear Technology, ISSN 0029-5450, E-ISSN 1943-7471, Vol. 191, nr 1, s. 58-70Artikel i tidskrift (Refereegranskat)
  • 137.
    Johansson, Per
    Högskolan Dalarna, Akademin Industri och samhälle, Materialteknik.
    Mekanisk och tribologisk karakterisering av ferrokrombaserat kompositmaterial för tribologiska användningsområden2014Självständigt arbete på grundnivå (kandidatexamen), 10 poäng / 15 hpStudentuppsats (Examensarbete)
  • 138.
    Johansson, Robert
    Högskolan Dalarna, Akademin Industri och samhälle, Materialteknik.
    Finite element modeling of straightening of thin-walled seamless tubes of austenitic stainless steel2016Självständigt arbete på grundnivå (kandidatexamen), 10 poäng / 15 hpStudentuppsats (Examensarbete)
    Abstract [en]

    During this thesis work a coupled thermo-mechanical finite element model (FEM) was builtto simulate hot rolling in the blooming mill at Sandvik Materials Technology (SMT) inSandviken. The blooming mill is the first in a long line of processes that continuously or ingotcast ingots are subjected to before becoming finished products.

    The aim of this thesis work was twofold. The first was to create a parameterized finiteelement (FE) model of the blooming mill. The commercial FE software package MSCMarc/Mentat was used to create this model and the programing language Python was used toparameterize it. Second, two different pass schedules (A and B) were studied and comparedusing the model. The two pass series were evaluated with focus on their ability to healcentreline porosity, i.e. to close voids in the centre of the ingot.

    This evaluation was made by studying the hydrostatic stress (σm), the von Mises stress (σeq)and the plastic strain (εp) in the centre of the ingot. From these parameters the stress triaxiality(Tx) and the hydrostatic integration parameter (Gm) were calculated for each pass in bothseries using two different transportation times (30 and 150 s) from the furnace. The relationbetween Gm and an analytical parameter (Δ) was also studied. This parameter is the ratiobetween the mean height of the ingot and the contact length between the rolls and the ingot,which is useful as a rule of thumb to determine the homogeneity or penetration of strain for aspecific pass.

    The pass series designed with fewer passes (B), many with greater reduction, was shown toachieve better void closure theoretically. It was also shown that a temperature gradient, whichis the result of a longer holding time between the furnace and the blooming mill leads toimproved void closure.

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  • 139. Karasev, A. V.
    et al.
    Kellner, Hans
    Högskolan Dalarna, Akademin Industri och samhälle, Materialteknik. KTH.
    Sundqvist, O.
    Memarpour, A.
    Jönsson, P. G.
    Estimation of non-metallic inclusions in industrial Ni based alloys 8252017Ingår i: Steel Research International, ISSN 1611-3683, E-ISSN 1869-344X, Vol. 88, nr 4, artikel-id 1600024Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    It is well known that inclusions affect the properties of the steel and other alloys. The importance of understanding the behavior of the inclusions during production can never be overstated. This study has examined the main types of big size (>10μm) inclusions that exist in Ni-based Alloy at the end of ladle treatment and after casting during industrial production of Ni based Alloys 825. Sources, mechanisms of formation and behavior of different type large size inclusions in Alloy 825 are discussed based on 2 and 3D investigations of inclusion characteristics (such as, morphology, composition, size, and number) and thermodynamic considerations. The large size inclusions found can be divided in spherical (Type I and II) inclusions and in clusters (Type III-V). Type I-A inclusions (Al2O3-CaO-MgO) originate from the slag. Type I-B inclusions and Type II inclusions consist of CaO-Al2O3-MgO and Al2O3-TiO2-CaO, respectively. Both types originate from the FeTi70R alloy. Type III clusters (Al2O3-MgO-CaO) are formed during an Al deoxidation of the Ni-based alloy. Type IV clusters (Al2O3-TiO2-CaO) formed from small inclusions, which are precipitated in local zones which contain high Ti and Al levels. These clusters are transformed to Type III clusters over time in the ladle. Finally, Type V clusters are typical TiN clusters. 

  • 140.
    Karimi Bakhshandi, Reza
    Högskolan Dalarna, Akademin Industri och samhälle, Materialteknik.
    Corrosion Study of yellowmetals in Biodiesel and Test fuel2014Självständigt arbete på avancerad nivå (masterexamen), 20 poäng / 30 hpStudentuppsats (Examensarbete)
    Abstract [en]

    Biodiesel is a promising substitute fuel for fossil fuels that derived from renewable resources like vegetable oils and animal fats. Rapeseed methyl ester, RME, is the most common biodiesel used in Scandinavia. Chemically, biodiesel is unstable and degradation of biodiesel results in formation of corrosive degradation products such as short chain fatty acids (SCFA) and water.Degradation of biodiesel is a continuous process which takes place even during corrosion studies in laboratory and results in too aggressive fuel. In order to investigate how increasing acidity of degraded fuel influence corrosion of metals and to avoid too corrosive environment, a stable test fuel simulating degraded biodiesel with certain amount of corrosive degradation products but resistance to additional degradation was needed to be developed.In the first part of this project a stable test fuel has been prepared and doped by adding impurity (methanol) and corrosive degradation products such as SCFA and water to a saturated methyl ester in order to simulate the corrosive environment and avoid excessive aggressiveness during the corrosion testing .Then four batches of test fuel were blended to see how increasing acidity and water content will influence the metallic corrosion.In the second part, samples of copper, brass and aluminium, with focus on copper, were exposed to prepared test fuels and RME in order to investigate corrosion behaviour of the metals and their effect on the test fuels.In order to investigate the stability of test fuel and effect of metals on it, developed test fuels were evaluated regarding to its water content using Karl Fischer volumetric titration, SCFA using extraction ion chromatography, structure using GC-MS and methanol using GC-FID. Targeted acceptance criteria for developed test fuel; such as solubility of degradation products, oxidation stability, toxicity, melting point were fulfilled by test fuel.Corrosion rate of the copper samples was calculated and their surfaces were analysed with SEM-EDS and FTIR. Metal content of fuel samples were analysed after exposure using ICP-OES method.As expected copper accelerated the oxidation of biodiesel effectively and copper ions were released into RME or low acidic test fuel but with increasing the acidity in test fuel copper samples were corroded and the corrosion rate increased. The results showed that the developed test fuel enabled accelerated corrosion testing comparable with aged RME.

  • 141.
    Karlsson, P
    et al.
    Karlstads Universitet.
    Eriksson, Jenny
    Högskolan Dalarna, Akademin Industri och samhälle, Materialteknik.
    Gaard, A
    Karlstads Universitet.
    Krakhmalev, P
    Karlstads Universitet.
    Olsson, Mikael
    Högskolan Dalarna, Akademin Industri och samhälle, Materialteknik.
    Bergstrom, J
    Karlstads Universitet.
    Galling resistance evaluation of tool steels by two different laboratory test methods for sheet metal forming2012Ingår i: Lubrication Science, ISSN 0954-0075, E-ISSN 1557-6833, Vol. 24, nr 6, s. 263-272Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Adhesive accumulation of work material on the tool surface is today a major problem in many sheet metal-forming applications. Different laboratory test methods are used to investigate galling with respect to different tool materials, lubricants and process conditions. In the present study, the galling resistance of a modern nitrogen-alloyed powder metallurgy tool steel and an conventional ingot cast D2 type tool steel was evaluated under lubricated sliding against ferritic stainless steel sheets using a commercial pin-on-disc (POD) and an in-house made slider-on-flat-surface (SOFS) tribotester. The investigated tool steels ranked similarly in terms of galling resistanc in both test methods. However, sliding distances to galling were longer for the SOFS equipment due to continuous sliding on new lubricated sheet surface. Best performance was demonstrated by the powder metallurgy tool steel treated to 65?HRC. Differences in friction behaviour and galling initiation were analysed on the basis of the two different working conditions, i.e. open (SOFS) and closed (POD) tribosystems. Copyright (c) 2012 John Wiley & Sons, Ltd.

  • 142. Karlsson, P. G.
    et al.
    Richter, J. H.
    Blomquist, J.
    Uvdal, P.
    Grehk, Mikael
    Högskolan Dalarna, Akademin Industri och samhälle, Materialvetenskap.
    Sandell, A.
    Metal organic chemical vapor deposition of ultrathin ZrO2 films on Si(1 0 0) and Si(1 1 1) studied by electron spectroscopy2007Ingår i: Surface Science, ISSN 0039-6028, E-ISSN 1879-2758, Vol. 601, nr 4, s. 1008-1018Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The growth of ultrathin ZrO2 films on Si(100)-(2x1) and Si(111)-(7x7) has been studied with core level photoelectron spectroscopy and X-ray absorption spectroscopy. The films were deposited sequentially by chemical vapor deposition in ultra-high vacuum using zirconium tetra-tert-butoxide as precursor. Deposition of a > 50Å thick film leads in both cases to tetragonal ZrO2 (t-ZrO2), whereas significant differences are found for thinner films. On Si(111)-(7x7) the local structure of t-ZrO2 is not observed until a film thickness of 51Å is reached. On Si(100)-(2x1) the local geometric structure of t-ZrO2 is formed already at a film thickness of 11Å. The higher tendency for the formation of t-ZrO2 on Si(100) is discussed in terms of Zr–O valence electron matching to the number of dangling bonds per surface Si atom. The Zr–O hybridization within the ZrO2 unit depends furthermore on the chemical composition of the surrounding. The precursor t-butoxy ligands undergo efficient C–O scission on Si(100), leaving carbonaceous fragments embedded in the interfacial layer. In contrast, after small deposits on Si(111) stable t-butoxy groups are found. These are consumed upon further deposition. Stable methyl and, possibly, also hydroxyl groups are found on both surfaces within a wide film thickness range.

  • 143.
    Karlström, Klaudia
    Högskolan Dalarna, Akademin Industri och samhälle, Materialteknik.
    Värmebehandling av kättingstål: Inverkan på slagsegheten och mikrostrukturen2014Självständigt arbete på grundnivå (kandidatexamen), 10 poäng / 15 hpStudentuppsats (Examensarbete)
    Abstract [sv]

    En av Ovakos interna stålsorter 9209 används till kättingar och har därmed höga krav på slagseghet och hårdhet. Efter ett antal kvalitetskontroller, där bland annat slagseghet och kornstorlek kontrollerats efter härdning med efterföljande anlöpning, har resultatet med slagsegheten vid -20 °C inte varit tillfredsställande. För att utreda orsaken till problemet har ett flertal härdtester i ett brett temperaturintervall utförts utan tillräckligt bra resultat. Vid ett tillfälle har materialet enkelglödgats i 720 °C i 135 minuter innan härdning. Detta har resulterat i förvånande höga värden på slagseghet. Det har även noterats att hårdheten ökar med ökad glödgningstemperatur.

    Huvudsyftet med arbetet är att genomföra värmebehandlingar i ett temperaturintervall för att hitta värmebehandlingstemperaturen som maximerar stålets egenskaper och att studera värmebehandlingens inverkan på mikrostrukturen.

    Resultatet av värmebehandlingarna visade att glödgningstemperaturen 700 °C var den enda som resulterade i godkända resultat på alla parametrar på den undersökta chargen.Den undersökta mikrostrukturen visade att glödgningens inverkan på utskiljda partiklar påverkar duktiliteten och på så vis förbättrar slagsegheten.Hårdhetsmätningarna visade att hårdheten ökade med glödgningstemperaturen.

  • 144. Kasimagwa, I.
    et al.
    Brabie, Voicu
    Högskolan Dalarna, Akademin Industri och samhälle, Materialteknik.
    Jonsson, P. G.
    Slag corrosion of MgO-C refractories during secondary steel refining2014Ingår i: Ironmaking & steelmaking, ISSN 0301-9233, E-ISSN 1743-2812, Vol. 41, nr 2, s. 121-131Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Studies of the reactions between the MgO-C refractory and a CaO-Al2O3-SiO2-MgO slag system have been carried out through thermodynamic simulations, laboratory experiments and microscopy studies of the microstructure of the refractory samples after the experimental procedures. Corrosion experiments were conducted using the rotating immersion method of the MgO-C refractory rods in a liquid slag: in the temperature range of 1773-1923 K, revolution speed of 200 rev min(-1), with varying slag compositions and times ( 2700-8100 s). Laboratory experiments have shown that the time during which the ladle lining is exposed to a liquid slag with high stirring and slag composition are two important parameters which have large effect on the kinetics of the refractory wear. The rate constants calculated in the present work are in the range of 4 x 10(-7) to 1 x 10(-6) ms(-1). The estimated activation energy from the experimental results is 26 kJ mol(-1)

  • 145.
    Kasimagwa, Ismail
    Högskolan Dalarna, Akademin Industri och samhälle, Materialvetenskap.
    A study of slag corrosion of oxides and oxide-carbon refractories during steel refining2010Doktorsavhandling, sammanläggning (Övrigt vetenskapligt)
    Abstract [en]

    The use of ceramic material as refractories in the manufacturing industry is a common practice worldwide. During usage, for example in the production of steel, these materials do experience severe working conditions including high temperatures, low pressures and corrosive environments. This results in lowered service lives and high consumptions of these materials. This, in turn, affects the productivity of the whole steel plant and thereby the cost. In order to investigate how the service life can be improved, studies have been carried out for refractories used in the inner lining of the steel ladles. More specifically, from the slag zone, where the corrosion is most severe. By combining thermodynamic simulations, plant trails and post-mortem studies of the refractories after service, vital information about the behaviour of the slagline refractories during steel refining and the causes of the accelerated wear in this ladle area has been achieved. The results from these studies show that the wear of the slagline refractories of the ladle is initiated at the preheating station, through reduction-oxidation reactions. The degree of the decarburization process is mostly dependent on the preheating fuel or the environment. For refractories without antioxidants, refractory decarburization is slower when coal gas is used in ladle preheating than when a mixture of oil and air is used. In addition, ladle preheating of the refractories without antioxidants leads to direct wear of the slagline refractories. This is due to the total loss of the matrix strength, which results in a sand-like product. Thermal chemical changes that take place in the slagline refractories are due to the MgO-C reaction as well as the formation of liquid phases from impurity oxides. In addition, the decrease in the system pressure during steel refining makes the MgO-C reaction take place at the steel refining temperatures. This reduces the refractory’s resistance to corrosion. This is a serious problem for both the magnesia-carbon and dolomite-carbon refractories. The studies of the reactions between the slagline refractories and the different slag compositions showed that slags rich in iron oxide lead mostly to the oxidation of carbon/graphite in the carbon-containing refractories. This leads to an increased porosity and wettability and therefore an enhanced penetration of slag into the refractory structure. If the slag contains high contents of alumina and or silica (such as the steel refining slag), reactions between the slag components and the dolomite-carbon refractory are promoted. This leads to the formation of low-temperature melting phases such as calcium-aluminates and silicates. The state of these reaction products during steel refining leads to an accelerated wear of the dolomite-carbon refractory. The main products of the reactions between the magnesia-carbon refractory and the steel refining slag are MgAl2O4 spinels, and calcium-aluminates, and silicates. Due to the good refractory properties of MgAl2O4 spinels, the slag corrosion resistance of the magnesiacarbon refractory is promoted.

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  • 146.
    Kasimagwa, Ismail
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad processmetallurgi.
    Brabie, Voicu
    Thermo-calc and SEM analysis of the dolomite lining during steel refining2008Ingår i: Proceedings for the Third Nordic Symposium for Young Scientists in Metallurgy, 2008, s. 46-50Konferensbidrag (Refereegranskat)
  • 147.
    Kasimagwa, Ismail
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad processmetallurgi.
    Brabie, Voicu
    Högskolan Dalarna, Akademin Industri och samhälle, Materialvetenskap.
    Jönsson, Pär G.
    Studies on decarburization of MgO-c refractories during ladle preheating2010Ingår i: Steel GRIPS Journal, ISSN 1611-4442, nr 8, s. 357-363Artikel i tidskrift (Refereegranskat)
  • 148.
    Kasimagwa, Ismail
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad processmetallurgi.
    Eriksson, J.
    Brabie, Voicu
    Wahlberg, H.
    Slagline refractory2008Ingår i: Proceedings for the SCANMET III-3rd International Conference on Process Development in Iron and Steel making, 2008, s. 377-384Konferensbidrag (Refereegranskat)
  • 149.
    Kellner, Hans
    Högskolan Dalarna, Akademin Industri och samhälle, Materialteknik. KTH, Tillämpad processmetallurgi.
    Study of Non-metallic Inclusion in Alloy 8252017Doktorsavhandling, sammanläggning (Övrigt vetenskapligt)
    Abstract [sv]

    Det är välkänt att inneslutningar påverkar egenskaperna i stål och legeringar. Därför är det viktigt att förstå vilken sorts inneslutningar som existerar samt hur de beter sig, särskilt stora inneslutningar. Således undersöktes de stora icke-metalliska inneslutningarna i ferrolegeringen FeTi70R i två dimensioner (2D) genom att använda svepelektronmikroskopi (SEM) i kombination med energidispersionsteknik (EDS). Det visade sig att ferrolegeringen FeTi70R innehåller komplexa oxidinneslutningar bestående huvudsakligen av CaO, Si02 och TiOx. Vidare utfördes laborativa försök för att undersöka hur dessa inneslutningar uppträder när de kommer ner i det smälta stålet. Mer specifikt så gjordes en jämförelse mellan rent Fe och Alloy 825 legeringen. Dessa resultat fastställde hur olika parametrar påverkade inneslutningarnas omvandling i smältan.

    De stora icke-metalliska inneslutningarna i Alloy 825 legeringen under skänkugnsbehandlingen undersöktes vid industriella försök med hjälp av både tvådimensionella (2D) och tredimensionella (3D) mikroskopiska undersökningar. Resultaten visade att inneslutningarna bestod av sfäriska oxider och kluster uppbyggda av oxider och nitrider. Ytterligare undersökningar visade att de sfäriska inneslutningarna omvandlades från befintliga icke-metalliska inneslutningar i ferrolegeringen FeTi70R och slaggpartiklar. När det gäller kluster härrör de från desoxidationsprodukter. Vidare så bildades små inneslutningar i de lokala zonerna kring den tillsatta FeTi70R legeringen och kring titanitriderna. Undersökningarna fann också att endast Al2O3-MgO och TiN-kluster existerar efter gjutning.

    De industriella försöken utfördes under den sista perioden av skänkugnsbehandlingen och med en kombinerad elektromagnetisk (EMS) och gas (GS) omröring. Syftet med detta var att undersöka effekten av olika riktningar på EMS omrörningen på agglomerationen och avskiljningen av Al2O3-MgO- och TiN klustren. Undersökningarna utfördes sedan i 3D efter en elektrolytisk extraktion av metallproverna. Resultaten visar att en uppåtriktad elektromagnetisk omröring är bäst för agglomereringen av Al2O3-MgO inneslutningar och TiN kluster. Emellertid så är en nedåtriktad elektromagnetisk omröring effektivare för att avlägsna kluster från smältan. Dessa resultat överensstämmer med de teoretiska förutsägelserna baserade på Stokes, Brownian och Turbulent kollisionsvolymer. Dessutom visade beräkningarna att för Al2O3-MgO kluster med storlekar <20 μm är det turbulenta kollisioner som är den avgörande faktorn för agglomerering. Dock är det både Stokes och de Turbulenta kollisionerna som dominerar för större inneslutningar. För TiN klustren är det de turbulenta kollisionerna som är den dominerande faktorn.

    Ytterligare undersökningar med fler charger av Alloy 825 och olika omrörningsmetoder gjordes baserade på 2D mikroskopiska undersökningar. Mer specifikt så bestämdes antalet, storleken, sammansättningen och morfologin för olika inneslutningar med användning av SEM i kombination med EDS och Inca Feature analyser. Resultaten visar att en nedåtriktad EMS i kombination med ett gasflöde på 0,04 m3 min-1 främjar ett generellt avlägsnande av Al2O3-MgO och TiN inneslutningar. Vidare främjar den uppåtriktade EMS omrörningen en drastisk ökning av inneslutningar med en ekvivalent storlek av 11,2 μm eller mindre. Vidare har omröringen med ett gasflöde på 0,02 m3 min-1 en bättre avskiljningshastighet för inneslutningar i både nedåt och uppåtgående omrörningsriktningar jämfört med omrörningen med ett gasflöde på 0,04 m3 min-1. Emellertid kunde inget inflytande på sammansättningen och morfologin ses från de olika omrörningssätten.

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  • 150.
    Kellner, Hans
    et al.
    Högskolan Dalarna, Akademin Industri och samhälle, Materialteknik.
    Karasev, A. V.
    Memarpour, A.
    Jönsson, P. G.
    Evolution of non-metallic inclusions from FeTi70R alloys during alloying of Fe-40Ni-20Cr steels2016Ingår i: Steel Research International, ISSN 1611-3683, E-ISSN 1869-344X, Vol. 87, nr 11, s. 1461-1468Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    In this study, the composition, size, and number of large non-metallic inclusions (&gt;20μm) are investigated in a commercial refined FeTi70R alloy, which is used for deoxidation and alloying of different industrial high-quality steels. It is found that this ferroalloy contains different complex oxide inclusions, which sizes vary from 20 to 260μm. These different complex inclusions contain mostly CaO, SiO2, and TiOx. When adding FeTi70R alloy in the steel during the final stage of ladle treatment, these large size inclusions can significantly decrease the cleanliness and mechanical properties of steel. Therefore, the evolution and behavior of these inclusions after addition of this ferroalloy into the liquid iron or Fe-40Ni-20Cr steel are investigated in laboratory experiments. In addition, the results from the laboratory scale experiments are compared to results obtained from industrial heats using Alloy 825. A consideration of the evolution mechanism of large inclusions after an addition of a FeTi70R alloy helps to understand their behavior in the melt. It also helps to estimate their possible harmful effects on the quality of this steel grade during commercial production. 

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