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  • 251.
    Valyukh, Sergiy
    et al.
    Högskolan Dalarna, Akademin Industri och samhälle, Materialteknik.
    Adas, C.
    Franklin, G.
    Skarp, K.
    Högskolan Dalarna, Akademin Industri och samhälle, Materialteknik.
    Measuring parameters of liquid crystal cells with MePaLC system2005Inngår i: IDMC 2005: Proceedings of the International Display Manufacturing Conference, 2005, s. 795-798Konferansepaper (Fagfellevurdert)
    Abstract [en]

    We present a sytem MePaLC for measuring retardation, its wavelength dispersion, twist angle, cell gap, and orientation of the input director. MePaLC enables us to measure practically all types of nematic liquid crystal cells: reflective and transmissive ones, with small and large cell gap.

  • 252.
    Valyukh, Sergiy
    et al.
    Högskolan Dalarna, Akademin Industri och samhälle, Materialteknik.
    Osterman, Jesper
    Högskolan Dalarna, Akademin Industri och samhälle, Materialvetenskap.
    Adås, C.
    Skarp, Kent
    Högskolan Dalarna, Akademin Industri och samhälle, Materialvetenskap.
    Cell gap measurements of flexible reflective TN- and STN-LC cells2004Inngår i: SID international symposium, 2004Konferansepaper (Fagfellevurdert)
  • 253.
    Valyukh, Sergiy
    et al.
    Högskolan Dalarna, Akademin Industri och samhälle, Materialteknik.
    Osterman, Jesper
    Högskolan Dalarna, Akademin Industri och samhälle, Materialvetenskap.
    Skarp, Kent
    Högskolan Dalarna, Akademin Industri och samhälle, Materialvetenskap.
    Simple Spectroscopic Method to Measure Cell Gap and Twist Angle of TN-LCD2003Inngår i: International display research conference, 2003Konferansepaper (Fagfellevurdert)
  • 254.
    Valyukh, Sergiy
    et al.
    Högskolan Dalarna, Akademin Industri och samhälle, Materialteknik.
    Osterman, Jesper
    Högskolan Dalarna, Akademin Industri och samhälle, Materialvetenskap.
    Skarp, Kent
    Högskolan Dalarna, Akademin Industri och samhälle, Materialvetenskap.
    Chigrinov, V.
    Optical performance of bistable reflective and transflective ferroelectric LCDs2005Inngår i: SID international symposium, Boston, 2005Konferansepaper (Fagfellevurdert)
  • 255.
    Valyukh, Sergiy
    et al.
    Högskolan Dalarna, Akademin Industri och samhälle, Materialteknik.
    Osterman, Jesper
    Högskolan Dalarna, Akademin Industri och samhälle, Materialvetenskap.
    Valyuhk, Iryna
    Högskolan Dalarna, Akademin Industri och samhälle, Materialvetenskap.
    Skarp, Kent
    Högskolan Dalarna, Akademin Industri och samhälle, Materialvetenskap.
    Characterization of flexible reflective liquid crystal cells2005Inngår i: Journal of the Society for Information Display, ISSN 1071-0922, E-ISSN 1938-3657, Vol. 13, nr 6, s. 501-506Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We consider peculiarities in testing flexible reflective liquid-crystal (LC) cells. Several new methods for measuring optical retardation of filled reflective LC cells on plastic substrates are proposed. Cases when the plastic is anisotropic and the LC cell consists of either one or two internal polarizers are studied. The majority of proposed methods can be applied for transmissive LC cells as well as for measuring twist angle.

  • 256.
    Valyukh, Sergiy
    et al.
    Högskolan Dalarna, Akademin Industri och samhälle, Materialteknik.
    Rybalochka, A.
    Sorokin, V.
    Slobodyanyuk, A.
    Spectroscopic method to measure cellgap of TN LC cells2002Inngår i: Proc. of Eurodisplay 2002, NiceArtikkel i tidsskrift (Annet vitenskapelig)
  • 257.
    Valyukh, Sergiy
    et al.
    Högskolan Dalarna, Akademin Industri och samhälle, Materialteknik.
    Rybalochka, A.
    Sorokin, V.
    Tytarenko, P.
    Skarp, Kent
    Högskolan Dalarna, Akademin Industri och samhälle, Materialvetenskap.
    A method for measuring reflective twist nematic liquid crystal cell properties2003Inngår i: Advanced display technologies, Moscow, Russia, 2003Konferansepaper (Fagfellevurdert)
  • 258.
    Valyukh, Sergiy
    et al.
    Högskolan Dalarna, Akademin Industri och samhälle, Materialteknik.
    Rybalochka, A
    Sorokin, V
    Tytarnenko, T
    Skarp, Kent
    Högskolan Dalarna, Akademin Industri och samhälle, Materialvetenskap.
    A method for measuring reflective twist nematic liquid crystal cell proporties2003Inngår i: Proceedings of XII International Symposium Advanced Display Technologies, Moscow, Russia, 2003, s. 254-257Konferansepaper (Fagfellevurdert)
  • 259.
    Valyukh, Sergiy
    et al.
    Högskolan Dalarna, Akademin Industri och samhälle, Materialteknik.
    Slobodyanyuk, A.
    Sorokin, V.
    Skarp, Kent
    Högskolan Dalarna, Akademin Industri och samhälle, Materialvetenskap.
    Computer simulation of scattering properties of cholesteric liquid crystal displays2001Inngår i: European conference on liquid crystals, Halle, Germany, 2001Konferansepaper (Annet vitenskapelig)
  • 260.
    Valyukh, Sergiy
    et al.
    Högskolan Dalarna, Akademin Industri och samhälle, Materialteknik.
    Valyuhk, Iryna
    Högskolan Dalarna, Akademin Industri och samhälle, Materialvetenskap.
    Skarp, Kent
    Högskolan Dalarna, Akademin Industri och samhälle, Materialteknik.
    Spectrophotometric determination of reflective liquid crystal cell parameters2006Inngår i: Journal of applied physiology, ISSN 8750-7587, E-ISSN 1522-1601, Vol. 99, nr 5Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We introduce a method for the determination of the optical retardation, its wavelength dispersion, the cell twist angle, and the orientation of the input director in a reflective liquid crystal (LC) cell. These parameters are found from the extremes of a characteristic function defined as a sum of two spectral reflectivities of the LC cell placed between a pair of linear polarizers. The reflectivities are measured for two cell orientations, one of which is arbitrary and the other one is turned through 45°. Both theoretical analysis and experimental procedures are presented. Excellent agreement between the experiment and our theory has been found. The proposed method can be applied to the measurement of reflective LC cells with small and large cell gaps, as well as cells with small and large twist angles.

  • 261.
    Valyukh, Sergiy
    et al.
    Högskolan Dalarna, Akademin Industri och samhälle, Materialteknik.
    Valyukh, Iryna
    Högskolan Dalarna, Akademin Industri och samhälle, Materialteknik.
    Adås, C.
    Chigrinov, V.
    Skarp, Kent
    Högskolan Dalarna, Akademin Industri och samhälle, Materialvetenskap.
    Reflective liquid crystal cell parameters2004Inngår i: Asia display, 2004Konferansepaper (Fagfellevurdert)
  • 262.
    Valyukh, Sergiy
    et al.
    Högskolan Dalarna, Akademin Industri och samhälle, Materialteknik.
    Valyukh, Iryna
    Högskolan Dalarna, Akademin Industri och samhälle, Materialteknik.
    Xu, Peizhi
    Chigrinov, Vladimir
    Study on birefringent color generation for a reflective ferroelectric liquid crystal display2006Inngår i: Japanese Journal of Applied Physics, ISSN 0021-4922, E-ISSN 1347-4065, Vol. 45, nr 10A, s. 7819-7826Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We study the possibility of a layer of a surface stabilized ferroelectric liquid crystal coupled with several retardation plates for birefringent color generation. Double and single polarizer reflective bistable dichromatic ferroelectric liquid crystal displays are considered. We demonstrate that one or two retardation plates are sufficient for a display having good color characteristics and high brightness. Optimal parameters for green/red and blue/yellow ferroelectric liquid crystal displays are found.

  • 263. Vattur Sundaram, M.
    et al.
    Surreddi, Kumar Babu
    Högskolan Dalarna, Akademin Industri och samhälle, Materialteknik.
    Hryha, E.
    Veiga, A.
    Berg, S.
    Castro, F.
    Nyborg, L.
    Enhanced densification of PM steels by liquid phase sintering with boron-containing master alloy2017Inngår i: Metallurgical and Materials Transactions. A, ISSN 1073-5623, E-ISSN 1543-1940, Vol. 49A, nr 1, s. 255-263Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Reaching high density in PM steels is important for high-performance applications. In this study, liquid phase sintering of PM steels by adding gas-atomized Ni-Mn-B master alloy was investigated for enhancing the density levels of Fe- and Mo- prealloyed steel powder compacts. The results indicated that liquid formation occurs in two stages, beginning with the master alloy melting (LP-1) below and eutectic phase formation (LP-2) above 1373 K (1100 °C). Mo and C addition revealed a significant influence on the LP-2 temperatures and hence on the final densification behavior and mechanical properties. Microstructural embrittlement occurs with the formation of continuous boride networks along the grain boundaries, and its severity increases with carbon addition, especially for 2.5 wt pct of master alloy content. Sintering behavior, along with liquid generation, microstructural characteristics, and mechanical testing revealed that the reduced master alloy content from 2.5 to 1.5 wt pct (reaching overall boron content from 0.2 to 0.12 wt pct) was necessary for obtaining good ductility with better mechanical properties. Sintering with Ni-Mn-B master alloy enables the sintering activation by liquid phase formation in two stages to attain high density in PM steels suitable for high-performance applications. © 2017 The Author(s)

  • 264.
    Vattur Sundaram, Maheswaran
    et al.
    Chalmers University of Technology.
    Surreddi, Kumar Babu
    Högskolan Dalarna, Akademin Industri och samhälle, Materialteknik.
    Hryha, Eduard
    Chalmers University of Technology.
    Veiga, Angela
    CEIT, Pº Manuel Lardizábal 15, 20018 San Sebastián, Spain.
    Berg, Siguard
    Höganäs AB, SE-263 83 Höganäs, Sweden.
    Castro, Francisco
    CEIT, Pº Manuel Lardizábal 15, 20018 San Sebastián, Spain.
    Nyborg, Lars
    Chalmers University of Technology.
    Full Densification in PM Steels Through Liquid Phase Sintering and HIP Approach2018Inngår i: Euro PM2018 Proceedings, 2018Konferansepaper (Fagfellevurdert)
    Abstract [en]

    High-density powder metallurgy (PM) components are required for high-performance applications. Liquid phase sintering (LPS) is one such method to improve the densification, especially the master alloy route is preferred due to the flexibility in tailoring the alloying contents. In this study, gas atomised Ni-Mn-B master alloy powder of size fraction < 45 µm was admixed with water atomised iron and Mo-prealloyed powder. During sintering, there was a significant densification due to LPS where the liquid formation occurred in two stages, one from the master alloy melting and another from the eutectic liquid formation, enabling densities > 95%. The microstructural investigation revealed that the surface densification was achieved after sintering in H2 containing atmosphere. Capsule free hot isostatic pressing was performed on these samples to achieve full density. This approach of combining LPS and capsule free hot isostatic pressing demonstrates the potential in reaching full densification in high-performance PM steel components.

  • 265. Vida, Á.
    et al.
    Maksa, Z.
    Molnar, David
    Högskolan Dalarna, Akademin Industri och samhälle, Materialteknik. KTH.
    Huang, S.
    Kovac, J.
    Varga, L. K.
    Vitos, L.
    Chinh, N. Q.
    Evolution of the phase structure after different heat treatments in NiCoFeCrGa high entropy alloy2018Inngår i: Journal of Alloys and Compounds, ISSN 0925-8388, E-ISSN 1873-4669, Vol. 743, s. 234-239Artikkel i tidsskrift (Fagfellevurdert)
  • 266. Wang, Z.
    et al.
    Prashanth, K. G.
    Surreddi, Kumar Babu
    Högskolan Dalarna, Akademin Industri och samhälle, Materialteknik.
    Suryanarayana, C.
    Eckert, J.
    Scudino, S.
    Pressure-assisted sintering of Al–Gd–Ni–Co amorphous alloy powders2018Inngår i: Materialia, ISSN 2589-1529, Vol. 2, s. 157-166Artikkel i tidsskrift (Fagfellevurdert)
  • 267.
    Westin, Tommy
    Högskolan Dalarna, Akademin Industri och samhälle, Materialvetenskap.
    Induktiv provning av ferritiskt rostfritt stå2011Independent thesis Advanced level (degree of Master (Two Years)), 20 poäng / 30 hpOppgave
    Abstract [en]

    The report examines the factors which may be a contributing cause to the problems that are present when ferritic stainless steel are eddy current tested in a warm condition. The work is carried out at Fagersta Stainless AB in Fagersta which manufactures stainless steel wire. In the rolling mill there is an eddy current equipment for detection of surface defects on the wire. The ferritic stainless steels cause a noise when testing and this noise complicates the detection of defects.Because of this, a study was made of how the noise related to factors such as steel grade, temperature, size and velocity. By observing the signal and with the possibilities to change the equipment settings the capability to let a signal filter reduce the noise level were evaluated. Theories about the material's physical properties have also been included, mainly the magnetic properties, electrical conductivity and the material's tendency to oxidize.Results from the tests show that a number of factors do not affect the inductive test significantly and to use a filter to reduce the noise level does not seem to be a viable option. The level of noise does not relate to the presence of superficial particles in form of oxides.The ferritic stainless steels showed some difference in noise level. Which noise level there was did match well with the steels probability for a precipitation of a second phase, and precipitation of austenite may in this case contribute to noise when using an eddy current instrument.The noise is probably due to some physical material property that varies within the thread.

  • 268.
    Westlund, V.
    et al.
    Uppsala Univ, Angstrom Tribomat Grp, Box 534, S-75121 Uppsala, Sweden..
    Heinrichs, J.
    Uppsala Univ, Angstrom Tribomat Grp, Box 534, S-75121 Uppsala, Sweden..
    Olsson, Mikael
    Högskolan Dalarna, Akademin Industri och samhälle, Materialteknik. Uppsala Univ, Angstrom Tribomat Grp, Box 534, S-75121 Uppsala, Sweden.
    Jacobson, S.
    Uppsala Univ, Angstrom Tribomat Grp, Box 534, S-75121 Uppsala, Sweden..
    Investigation of material transfer in sliding friction-topography or surface chemistry?2016Inngår i: Tribology International, ISSN 0301-679X, E-ISSN 1879-2464, Vol. 100, s. 213-223Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    To differentiate between the roles of surface topography and chemical composition on influencing friction and transfer in sliding contact, a series of tests were performed in situ in an SEM. The initial sliding during metal forming was investigated, using an aluminum tip representing the work material, put into sliding contact with a polished flat tool material. Both DLC-coated and uncoated tool steel was used. By varying the final polishing step of the tool material, different surface topographies were obtained. The study demonstrates the strong influence from nano topography of an unpolished DLC coated surface on both coefficient of friction and material transfer. The influence of tool surface chemistry is also discussed.

  • 269.
    Wiklund, Urban
    et al.
    Uppsala University.
    Olsson, Mikael
    Högskolan Dalarna, Akademin Industri och samhälle, Materialteknik.
    Jacobson, Staffan
    Uppsala University.
    Degradation mechanisms of matrix steel in rock drill bits2016Inngår i: Proceedings of the 17th Nordic Symposium on Tribology - Nordtrib 2016, 2016Konferansepaper (Fagfellevurdert)
  • 270. Wikström, Lars
    et al.
    Bexell, Ulf
    Högskolan Dalarna, Akademin Industri och samhälle, Materialteknik.
    Lindgren, Michael
    Högskolan Dalarna, Akademin Industri och samhälle, Materialteknik.
    Partial annealing of stainless steel before roll forming2007Inngår i: Stål 2007, 2007Konferansepaper (Annet vitenskapelig)
  • 271.
    Yvell, Karin
    Högskolan Dalarna, Akademin Industri och samhälle, Materialteknik. KTH, Materialvetenskap.
    Experimental Studies of Deformation Structures in Stainless Steels using EBSD2018Doktoravhandling, med artikler (Annet vitenskapelig)
    Abstract [en]

    In this thesis, the focus has been the study of deformation structures in stainless steels by using electron backscatter diffraction (EBSD). Via increased knowledge of the evolution of the substructure during deformation, the design and control of the manufacturing process can be improved.

    A relation was found between the active deformation mechanisms, the evolution of low angle boundaries (LABs) and the strain hardening rate. When deformation twinning was an active deformation mechanism in an austenitic stainless steel with lower stacking fault energy (SFE), the strain hardening rate was maintained up to large strains due to formation of LABs. The deformation twin boundaries acted as new obstacles for dislocation slip which in turn increased the formation of LABs even further. During deformation by slip in an austenitic stainless steel with a higher SFE, the strain hardening rate instead decreased when LABs were formed. A high value of SFE promotes dislocation cross slip which in turn increases annihilation of dislocations leading to a minor increase in LAB formation.

    Deformation structures formed in surface grains during in situ tensile tests were found to develop at lower strains than in bulk grains obtained from interrupted conventional tensile tests. This behavior is consistent with the fact that dislocations sources and deformation twinning operate at approximately half the stress on a free surface as compared to the bulk.

    The deformation structures were quantified by measuring size distributions for entities bounded by LABs and high angle boundaries (HABs). The size distributions were found to be well described by bimodal lognormal distribution functions. The average size for the distribution of small grains and subgrains correlated well with the mean free distance of dislocation slip and to the strain hardening.

  • 272.
    Yvell, Karin
    et al.
    Högskolan Dalarna, Akademin Industri och samhälle, Materialteknik. KTH, Materialvetenskap.
    Engberg, Göran
    Högskolan Dalarna, Akademin Industri och samhälle, Materialteknik.
    Deformation structures in a duplex stainless steel2018Inngår i: Materials Science Forum, ISSN 0255-5476, E-ISSN 1662-9752, Vol. 941, s. 176-181Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The evolution of the deformation structure with strain has been studied using electron backscatter diffraction (EBSD). Samples from interrupted uniaxial tensile tests and from a cyclic tension/compression test were investigated. The evolution of low angle boundaries (LABs) was studied using boundary maps and by measuring the LAB density. From calculations of local misorientations, smaller orientation changes in the substructure can be illustrated. The different orientations developed with strain within a grain, due to operation of different slip systems in different parts of the grain, were studied using a misorientation profile showing substantial orientation changes after a true strain of 0.24. The texture evolution with increasing strain was followed by using inverse pole figures (IPFs). The observed substructure development in the ferritic and austenitic phases could be successfully correlated with the stress-strain curve from a tensile test. LABs were first observed in the different phases when the strain hardening rate changed in appearance indicating that cross slip started to operate as a significant dislocation recovery mechanism. The evolution of the deformation structure is concluded to occur in a similar manner in the austenitic and ferritic phases but with different texture evolution for the two phases.

  • 273.
    Yvell, Karin
    et al.
    Högskolan Dalarna, Akademin Industri och samhälle, Materialteknik.
    Engberg, Göran
    Högskolan Dalarna, Akademin Industri och samhälle, Materialteknik.
    Microstructure evolution in an austenitic stainless steel during wire rolling2013Inngår i: Materials Science Forum, ISSN 0255-5476, E-ISSN 1662-9752, Vol. 753, s. 407-410Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Material characterization is of great importance for example to improve and further develop physically based models for predicting the microstructural evolution in steels during and after hot deformation. The aim of this study was to characterize the microstructure evolution during wire rod rolling of an austenitic stainless steel of type AISI 304L in a wire rod block, consisting of eight pairs of rolls, using electron backscatter diffraction. The investigation showed that the grain size in the center of the bar decreases during the first four passes. The grain size decrease from 6.5 Όm after the first roll pass down to 2 Όm, and only small changes was measured in the overall grain size during the last four passes. The subgrain size adopts an almost constant size of 0.9 Όm from the second until the fifth roll pass. During the first 3 passes almost no recrystallization is observed and strain accumulates. Partial recrystallization then starts and for the last 3 passes the recrystallization is almost complete and the texture is nearly random. © (2013) Trans Tech Publications, Switzerland.

  • 274.
    Yvell, Karin
    et al.
    Högskolan Dalarna, Akademin Industri och samhälle, Materialteknik.
    Grehk, T. M.
    Engberg, Göran
    Högskolan Dalarna, Akademin Industri och samhälle, Materialteknik.
    Microstructure characterization of 316L deformed at high strain rates using EBSD2016Inngår i: Materials Characterization, ISSN 1044-5803, E-ISSN 1873-4189, Vol. 122, s. 14-21Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Specimens from split Hopkinson pressure bar experiments, at strain rates between ~ 1000–9000 s− 1 at room temperature and 500 °C, have been studied using electron backscatter diffraction. No significant differences in the microstructures were observed at different strain rates, but were observed for different strains and temperatures. Size distribution for subgrains with boundary misorientations > 2° can be described as a bimodal lognormal area distribution. The distributions were found to change due to deformation. Part of the distribution describing the large subgrains decreased while the distribution for the small subgrains increased. This is in accordance with deformation being heterogeneous and successively spreading into the undeformed part of individual grains. The variation of the average size for the small subgrain distribution varies with strain but not with strain rate in the tested interval. The mean free distance for dislocation slip, interpreted here as the average size of the distribution of small subgrains, displays a variation with plastic strain which is in accordance with the different stages in the stress-strain curves. The rate of deformation hardening in the linear hardening range is accurately calculated using the variation of the small subgrain size with strain.

  • 275.
    Yvell, Karin
    et al.
    Högskolan Dalarna, Akademin Industri och samhälle, Materialteknik.
    Grehk, T. M.
    Hedström, P.
    Borgenstam, A.
    Engberg, Göran
    Högskolan Dalarna, Akademin Industri och samhälle, Materialteknik.
    EBSD analysis of surface and bulk microstructure evolution during interrupted tensile testing of a Fe-19Cr-12Ni alloy2018Inngår i: Materials Characterization, ISSN 1044-5803, E-ISSN 1873-4189, Vol. 141, s. 8-18Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Abstract The microstructure evolution in both surface and bulk grains in a pure Fe-19Cr-12Ni alloy has been analyzed using electron backscatter diffraction after tensile testing interrupted at different strains. Surface grains were studied during in situ tensile testing performed in a scanning electron microscope, whereas bulk grains were studied after conventional tensile testing. The evolution of the deformation structure in surface and bulk grains displays a strong resemblance but the strain needed to obtain a similar deformation structure is lower in the case of surface grains. Both slip and twinning are observed to be important deformation mechanisms, whereas deformation-induced martensite formation is of minor importance. Since the stacking fault energy (SFE) is low, 17mJ/m2, dynamic recovery by cross slip of un-dissociated dislocations is unfavorable. This reduces the annihilation of dislocations which in turn leads to a significant increase of low angle boundaries with increasing strain. The low SFE also favors formation of deformation twins which reduces the slip distance, leading to a hardening similar to the Hall-Petch relation. The combination of a low ability for cross-slip and a reduced slip distance caused by twinning is concluded to be the main reason for maintaining a high strain-hardening rate up to strains close to necking.

  • 276.
    Yvell, Karin
    et al.
    Högskolan Dalarna, Akademin Industri och samhälle, Materialteknik.
    Grehk, T. M.
    Hedström, P.
    Borgenstam, A.
    Engberg, Göran
    Högskolan Dalarna, Akademin Industri och samhälle, Materialteknik.
    Microstructure development in a high-nickel austenitic stainless steel using EBSD during in situ tensile deformation2018Inngår i: Materials Characterization, ISSN 1044-5803, E-ISSN 1873-4189, Vol. 135, nr Supplement C, s. 228-237Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Plastic deformation of surface grains has been observed by electron backscatter diffraction technique during in situ tensile testing of a high-nickel austenitic stainless steel. The evolution of low- and high-angle boundaries as well as the orientation changes within individual grains has been studied. The number of low-angle boundaries and their respective misorientation increases with increasing strain and some of them also evolve into high-angle boundaries leading to grain fragmentation. The annealing twin boundaries successively lose their integrity with increasing strain. The changes in individual grains are characterized by an increasing spread of orientations and by grains moving towards more stable orientations with 〈111〉 or 〈001〉 parallel to the tensile direction. No deformation twins were observed and deformation was assumed to be caused by dislocation slip only.

  • 277.
    Yvell, Karin
    et al.
    Högskolan Dalarna, Akademin Industri och samhälle, Materialteknik.
    Lindgren, Michael
    Bexell, Ulf
    Högskolan Dalarna, Akademin Industri och samhälle, Materialteknik.
    A microstructural investigation of roll formed austenitic stainless steel2013Inngår i: Sheet metal 2013: Key engineering metals, 2013, Vol. 549, s. 364-371Konferansepaper (Fagfellevurdert)
    Abstract [en]

    Due to high production rates and the possibility to form complex geometries roll forming has become an increasingly popular forming process for sheet metal. Increasing quantities of high strength steels are used today but can be difficult to form due to their low ductility. One way to partly overcome this problem is to heat the steel in the forming area thus locally increasing the ductility. In the present study partially heated cold rolled high strength AISI 301 type austenitic stainless steel was investigated using electron backscattered diffraction (EBSD), and the results were compared to microhardness measurements. The results show that partial heating will give an almost complete reverse martensite transformation, i.e. martensite (alpha') transforms to austenite (gamma), close to the surfaces and grain growth in the middle of the steel sheet. The extension of the heat affected zone can be determined using either microhardness or EBSD measurements. Both these measurements can be used to determine the position of the neutral layer after roll forming. The hardness measurement cannot distinguish between microstructural features but the results are in good agreement with the EBSD results for volume fraction of alpha'-martensite. A major advantage of using EBSD is the possibility to characterize and follow the microstructural development when heating and roll forming.

  • 278.
    Zhou, Nian
    Högskolan Dalarna, Akademin Industri och samhälle, Materialteknik. KTH, Yt- och korrosionsvetenskap.
    Surface integrity and corrosion behavior of stainless steels after grinding operations2018Doktoravhandling, med artikler (Annet vitenskapelig)
    Abstract [en]

    Stainless steels are widely used in applications where both the mechanical properties of steels and high corrosion resistance are required. There is continuous research to enable stainless steel components to be produced in a more economical way and be used in more harsh environments. A way to achieve this is to correlate the service performance with the production processes.

    The central theme of this thesis is surface integrity and corrosion, especially the stress corrosion cracking behavior, after grinding processes. Controlled grinding parameters, including abrasive grit size, machine power and grinding lubricant, were used and the resulting surface properties studied for austenitic 304L and duplex 2304 stainless steels. The abrasive grit size effect was found to have a larger influence. Surface defects, a highly deformed surface layer and the generation of a high level surface tensile residual stresses along the grinding direction were observed as the main types of damage. 

    The effect of grinding on stress corrosion cracking behavior of austenitic 304L, ferritic 4509 and duplex 2304 stainless steels in chloride-containing environments was also investigated.  The abrasive grit size effect on corrosion behavior for the three grades was compared. Grinding-induced surface tensile residual stress was suggested as the main factor to cause micro-cracks on the ground surface for 304L and 2304; for 4509, grinding-induced grain fragmentation was considered as the main factor for the initiation of extensive micro-pits. For duplex 2304, the microstructure and micro-notches in the as-ground surface also had significant influence. Depending on the surface conditions, the actual loading by four-point bending was found to deviate from the calculated value using the formula according to ASTM G39 by different amounts. The knowledge obtained from this work can provide guidance for choosing appropriate stainless steel grades and grinding parameters; and can also be used to help understanding the failure mechanism of ground stainless steel components during service.

  • 279.
    Zhou, Nian
    et al.
    Högskolan Dalarna, Akademin Industri och samhälle, Materialteknik. KTH.
    Lin Peng, Ru
    Linköping University.
    Pettersson, Rachel
    Jernkontoret, KTH.
    Surface characterization of austenitic stainless steel 304L after different grinding operations2017Inngår i: International Journal of Mechanical and Materials Engineering, ISSN 2198-2791, Vol. 12, nr 6Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Background: The austenitic stainless steel 304L is widely used as a structural material for which the finished surface has significant effect on the service performance. A study of the grinding process with regard to the quality of the ground surfaces is therefore interesting from the point of view of both industrial application and scientific research.

    Method: This work investigates the influence of grinding parameters including abrasive grit size, machine power, and grinding lubrication on the surface integrity of the austenitic stainless steel 304L. The induced normal grinding force, grinding surface temperature, metal removal rate, and surface property changes have been investigated and compared.

    Results and Conclusion: Using grinding, lubrication significantly enhanced the metal removal rate. Surface defects (deep grooves, smearing, adhesive chips, and indentations), a highly deformed thin surface layer up to a few microns in thickness, and high surface tensile residual stresses parallel to the grinding direction have been observed as the main damage induced by the grinding operations. Surface finish and deformation were found to be improved by using smaller abrasive grits or by using lubrication during grinding. Increasing the machine power increased surface deformation while reducing surface defects. The results obtained can provide a reference for choosing appropriate grinding parameters when machining 304L; and can also help to understand the failure mechanism of ground austenitic stainless steel components during service.

  • 280.
    Zhou, Nian
    et al.
    Högskolan Dalarna, Akademin Industri och samhälle, Materialteknik. KTH.
    Lin Peng, Ru
    Linköping University.
    Pettersson, Rachel
    Jernkontoret, KTH.
    Schönning, Mikael
    Avesta Research Center - Outokumpu Stainless AB.
    Residual stress in stainless steels after surface grinding and its effect on chloride induced SCC2016Inngår i: Materials Research Proceedings: Residual Stresses 2016: ICRS-10, 2016, s. 289-294Konferansepaper (Fagfellevurdert)
    Abstract [en]

    The induced residual stresses in stainless steels as a consequence of surface grinding as well as their influence on the chloride induced stress corrosion cracking (SCC) susceptibility have been investigated. Three types of materials were studied: 304L austenitic stainless steel, 4509 ferritic stainless steel and 2304 duplex stainless steel. Surface grinding using 60# and 180# grit size abrasives was performed for each material. Residual stress depth profiles were measured using X-ray diffraction. The susceptibility to stress corrosion cracking was evaluated in boiling MgCl2 according to ASTM G36. Specimens were exposed without applying any external loading to evaluate the risk for SCC caused solely by residual stresses. Induced residual stresses and corrosion behavior were compared between the austenitic, ferritic and duplex stainless steels to elucidate the role of the duplex structure. For all materials, the grinding operation generated tensile residual stresses in the surface along the grinding direction but compressive residual stresses perpendicular to the grinding direction. In the subsurface region, compressive stresses in both directions were present. Micro-cracks initiated due to high grinding-induced tensile residual stresses in the surface layer were observed in austenitic 304L and duplex 2304, but not in the ferritic 4509. The surface residual stresses decreased significantly after exposure for all specimens.

  • 281.
    Zhou, Nian
    et al.
    Högskolan Dalarna, Akademin Industri och samhälle, Materialteknik. KTH.
    Lin Peng, Ru
    Linköping University.
    Schönning, Mikael
    Avesta Research Center–Outokumpu Stainlelss AB.
    Pettersson, Rachel
    Jernkontoret, KTH.
    SCC of 2304 duplex stainless steel - microstructure, residual stress and surface grinding effects2017Inngår i: Materials, ISSN 1996-1944, E-ISSN 1996-1944, Vol. 10, nr 3, artikkel-id 221Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The influence of surface grinding and microstructure on chloride induced stress corrosion cracking (SCC) behavior of 2304 duplex stainless steel has been investigated. Grinding operations were performed both parallel and perpendicular to the rolling direction of the material. SCC tests were conducted in boiling magnesium chloride according to ASTM G36; specimens were exposed both without external loading and with varied levels of four-point bend loading. Residual stresses were measured on selected specimens before and after exposure using the X-ray diffraction technique. In addition, in-situ surface stress measurements subjected to four-point bend loading were performed to evaluate the deviation between the actual applied loading and the calculated values according to ASTM G39. Micro-cracks, initiated by grinding induced surface tensile residual stresses, were observed for all the ground specimens but not on the as-delivered surfaces. Loading transverse to the rolling direction of the material increased the susceptibility to chloride induced SCC. Grinding induced tensile residual stresses and micro-notches in the as-ground surface topography were also detrimental.

  • 282.
    Zhou, Nian
    et al.
    Högskolan Dalarna, Akademin Industri och samhälle, Materialteknik.
    Peng, R. L.
    Pettersson, R.
    Surface integrity of 2304 duplex stainless steel after different grinding operations2016Inngår i: Journal of Materials Processing Technology, ISSN 0924-0136, E-ISSN 1873-4774, Vol. 229, s. 294-304Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Surface integrity has significant effect on service performance of a component. In this study, the evolution of the surface and sub-surface changes induced by grinding duplex stainless steel (DSS) 2304 was studied with regard to the residual stress, the microstructure, surface roughness and surface defects. The results provide insights into the effect of abrasive grit size, grinding force and lubrication on the surface integrity. The abrasive grit size was found to have the largest influence. Surface defects, a highly deformed surface layer and the generation of tensile residual stresses along the grinding direction have been found to be the main types of damage induced by the grinding operation. Residual stresses induced by mechanical effects dominate over thermal effects in this study. The results obtained can be used to understand the contribution of surface condition and residual stress on failure of duplex stainless steels in service by fatigue or stress corrosion cracking.

  • 283.
    Zhou, Nian
    et al.
    Högskolan Dalarna, Akademin Industri och samhälle, Materialteknik. KTH.
    Pettersson, R.
    Schönning, M.
    Peng, R. L.
    Influence of surface grinding on corrosion behavior of ferritic stainless steels in boiling magnesium chloride solution2018Inngår i: Materials and corrosion - Werkstoffe und Korrosion, ISSN 0947-5117, E-ISSN 1521-4176, Vol. 69, nr 11, s. 1560-1571Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The influence of grinding operations on surface properties and corrosion behavior of a ferritic stainless steel (FSS), EN 1.4509, has been investigated and limited comparisons also made to the grade EN 1.4622. Surface grinding was performed along the rolling direction of the material. Corrosion tests were conducted in boiling magnesium chloride solution according to ASTM G36; specimens were exposed both without external loading and under four‐point bend loading. The surface topography and cross‐section microstructure before and after exposure were investigated, and residual stresses were measured on selected specimens before and after corrosion tests using X‐ray diffraction. In addition, in situ surface stress measurements were performed to evaluate the actual surface stresses of specimens subject to four‐point bend loading according to ASTM G39. Micro‐pits showing branched morphology initiated from the highly deformed ground surface layer which contained fragmented grains, were observed for all the ground specimens but not those in the as‐delivered condition. Grain boundaries under the surface layer appeared to hinder the corrosion process. No macro‐cracking was found on any specimen after exposure even at high calculated applied loads.

  • 284.
    Zhou, Nian
    et al.
    Högskolan Dalarna, Akademin Industri och samhälle, Materialteknik. KTH.
    Pettersson, Rachel
    KTH; Jernkontoret.
    Peng, Ru Lin
    Linköping universitet.
    Schonning, Mikael
    Outokumpu Stainless AB, Avesta.
    Effect of surface grinding on chloride induced SCC of 304L2016Inngår i: Materials Science & Engineering: A, ISSN 0921-5093, E-ISSN 1873-4936, Vol. 658, s. 50-59Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The effect of surface grinding on the stress corrosion cracking (SCC) behavior of 304L austenitic stainless steel in boiling magnesium chloride has been investigated. SCC tests were conducted both without external loading and with varied levels of four-point bend loading for as-delivered material and for specimens which had been ground parallel or perpendicular to the loading direction. Residual stresses due to the grinding operation were measured using the X-ray diffraction technique. In addition, surface stress measurements under applied load were performed before exposure to evaluate the deviation between actual applied loading and calculated values according to ASTM G39. Micro-cracks initiated by a high level of tensile residual stress in the surface layer were observed for all the ground specimens but not those in the as-delivered condition. Grinding along the loading direction increased the susceptibility to chloride induced SCC; while grinding perpendicular to the loading direction improved SCC resistance. Surface tensile residual stresses were largely relieved after the initiation of cracks. (C) 2016 Elsevier B.V. All rights reserved.

  • 285.
    Ångström, Carl-Johan
    et al.
    Högskolan Dalarna, Akademin Industri och samhälle, Materialteknik.
    Karlsson, Johan
    Högskolan Dalarna, Akademin Industri och samhälle, Materialteknik.
    Studie av fasomvandlingar vid värmebehandling av bi-metallblad i kontinuerlig process2014Independent thesis Basic level (degree of Bachelor), 10 poäng / 15 hpOppgave
    Abstract [sv]

    Håkansson Sågblad tillverkar i dagsläget sågblad av bimetalltyp för kapning i metall, där en del av bladet består av varmarbetsstål och en annan av snabbstål. Håkansson har investerat i en ny ugnslinje för snabbanlöpning. Anlöpningsparametrarna för den nya ugnen är i optimeringsfasen.

    Arbetets syfte var att studera de fasomvandlingar som sker i materialet vid de värmebehandlingsoperationer som det utsätts för, utöver det skall även ett lösningsförslag för anlöpningsparametrarna tas fram. För att kunna uppfylla arbetets syfte har studier av material från både den nya och den äldre ugnslinjen genomförts, där fokus ligger på snabbstålet i sågtanden. Materialet studerades sedan i mikroskop och hårdhetsmättes. Strukturen i tandspetsen identifierades som en restaustenitisk, martensitisk grundmassa med utfällda karbider, där halterna av de olika strukturerna varierade med olika prov. Hårdhetsmässigt låg proven mellan 920 och 970 HV, vilket var inom förväntat intervall. Proverna från den nya ugnen med den högre hastigheten innehåller en mängd restaustenit som gör att hårdheten ökar vid en ytterligare anlöpning.

    Anlöpningsparametrarna bör förändras för att undvika att leveransklart material innehåller denna mängd restaustenit. Detta kan på ett fördelaktigt sätt ske genom en temperaturhöjning i ugnen eller genom en höjning av temperaturen i det förvärmningsaggregat som ingår i anlöpningsutrustningen.

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