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  • 1.
    Balachandramurthi, Arun Ramanathan
    et al.
    Univ West, Sweden.
    Moverare, Johan
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, Faculty of Science & Engineering. Univ West, Sweden.
    Dixit, Nikhil
    Univ West, Sweden.
    Pederson, Robert
    Univ West, Sweden.
    Influence of defects and as-built surface roughness on fatigue properties of additively manufactured Alloy 7182018In: Materials Science & Engineering: A, ISSN 0921-5093, E-ISSN 1873-4936, Vol. 735, p. 463-474Article in journal (Refereed)
    Abstract [en]

    Electron beam melting (EBM) and Selective Laser Melting (SLM) are powder bed based additive manufacturing (AM) processes. These, relatively new, processes offer advantages such as near net shaping, manufacturing complex geometries with a design space that was previously not accessible with conventional manufacturing processes, part consolidation to reduce number of assemblies, shorter time to market etc. The aerospace and gas turbine industries have shown interest in the EBM and the SLM processes to enable topology-optimized designs, parts with lattice structures and part consolidation. However, to realize such advantages, factors affecting the mechanical properties must be well understood - especially the fatigue properties. In the context of fatigue performance, apart from the effect of different phases in the material, the effect of defects in terms of both the amount and distribution and the effect of "rough" as-built surface must be studied in detail. Fatigue properties of Alloy 718, a Ni-Fe based superalloy widely used in the aerospace engines is investigated in this study. Four point bending fatigue tests have been performed at 20 Hz in room temperature at different stress ranges to compare the performance of the EBM and the SLM material to the wrought material. The experiment aims to assess the differences in fatigue properties between the two powder bed AM processes as well as assess the effect of two post-treatment methods namely - machining and hot isostatic pressing (HIP). Fractography and metallography have been performed to explain the observed properties. Both HIPing and machining improve the fatigue performance; however, a large scatter is observed for machined specimens. Fatigue properties of SLM material approach that of wrought material while in EBM material defects severely affect the fatigue life.

  • 2.
    Borlado, C R
    et al.
    Inst de Ciencia de Materiales de Madrid Madrid.
    Mompean, F J
    Inst de Ciencia de Materiales de Madrid Madrid.
    Peng, Ru
    Linköping University, The Institute of Technology. Linköping University, Department of Mechanical Engineering, Engineering Materials.
    Izquierdo, J
    IBERDROLA Madrid.
    Roman, M A
    Babcock and Wilcox Galindo.
    Lopez Serrano, V
    Centro Nacional de Investigaciones Metalurgicas Madrid.
    Neutron strain scannin gon bimetallic tubes2000In: Materials Science & Engineering: A, ISSN 0921-5093, E-ISSN 1873-4936, Vol. 288, p. 288-292Article in journal (Refereed)
  • 3.
    Brodin, Håkan
    et al.
    Linköping University, Department of Mechanical Engineering, Engineering Materials. Linköping University, The Institute of Technology.
    Eskner, Mats
    Material Science KTH.
    High Temperature Elastic-Plastic Behaviour of a Vacuum Plasma-Sprayed NiCrAlY Coating by Spherical Indentation and Small Punch Tests1998In: Materials Science & Engineering: A, ISSN 0921-5093, E-ISSN 1873-4936Article in journal (Refereed)
  • 4.
    Ceschini, Lorella
    et al.
    Dept of Industrial Engineering (DIN), University of Bologa, Italy.
    Morri, Alessandro
    Dept of Industrial Engineering (DIN), University of Bologna, Italy.
    Toschi, Stefania
    Dept of Industrial Engineering (DIN), University of Bologna, Italy.
    Johansson, Sten
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, Faculty of Science & Engineering.
    Seifeddine, Salem
    Dept of Materials and Manufacturing, Jönköping University.
    Microstructural and Mechanical Properties Characterization of Heat Treated and Overaged Cast A354 Alloy with Various SDAS at Room and Elevated Temperature2015In: Materials Science & Engineering: A, ISSN 0921-5093, E-ISSN 1873-4936, Vol. 648, p. 340-349Article in journal (Refereed)
    Abstract [en]

    The aim of the present study was to carry out a microstructural and mechanical characterization of the A354 (Al–Si–Cu–Mg) cast aluminum alloy. The effect of microstructure on the tensile behavior was evaluated by testing samples with different Secondary Dendrite Arm Spacing, (SDAS) values (20–25 μm and 50–70 μm for fine and coarse microstructure, respectively), which were produced through controlled casting conditions. The tensile behavior of the alloy was evaluated both at room and elevated temperature (200 °C), in the heat treated and overaged (exposure at 210 °C for 41 h, after heat treatment) conditions. Optical, scanning electron microscopy (SEM) and scanning transmission electron microscopy (STEM) were used for microstructural investigations.

    Experimental data confirmed the significant role of microstructural coarseness on the tensile behavior of A354 alloy. Ultimate tensile strength and elongation to failure strongly increased with the decrease of SDAS. Moreover, solidification rate influenced other microstructural features, such as the eutectic silicon morphology as well as the size of the intermetallic phases, which in turn also influenced elongation to failure. Coarsening of the strengthening precipitates was induced by overaging, as observed by STEM analyses, thus leading to a strong reduction of the tensile strength of the alloy, regardless of SDAS. Tensile properties of the alloy sensibly decrease at elevated temperature (200 °C) in all the investigated heat treatment conditions.

  • 5.
    Chen, Zhe
    et al.
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, Faculty of Science & Engineering.
    Hörnqvist Colliander, Magnus
    Department of Physics, Chalmers University of Technology, Gothenburg, Sweden.
    Sundell, Gustav
    Department of Physics, Chalmers University of Technology, Gothenburg, Sweden.
    Peng, Ru
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, Faculty of Science & Engineering.
    Zhou, Jinming
    Division of Production and Materials Engineering, Lund University, Sweden.
    Johansson, Sten
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, Faculty of Science & Engineering.
    Moverare, Johan
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, Faculty of Science & Engineering.
    Nano-scale characterization of white layer in broached Inconel 7182017In: Materials Science & Engineering: A, ISSN 0921-5093, E-ISSN 1873-4936, Vol. 684, p. 373-384Article in journal (Refereed)
    Abstract [sv]

    The formation mechanism of white layers during broaching and their mechanical properties are not well investigated and understood to date. In the present study, multiple advanced characterization techniques with nano-scale resolution, including transmission electron microscopy (TEM), transmission Kikuchi diffraction (TKD), atom probe tomography (APT) as well as nano-indentation, have been used to systematically examine the microstructural evolution and corresponding mechanical properties of a surface white layer formed when broaching the nickel-based superalloy Inconel 718.

    TEM observations showed that the broached white layer consists of nano-sized grains, mostly in the range of 20–50 nm. The crystallographic texture detected by TKD further revealed that the refined microstructure is primarily caused by strong shear deformation. Co-located Al-rich and Nb-rich fine clusters have been identified by APT, which are most likely to be γ′ and γ′′ clusters in a form of co-precipitates, where the clusters showed elongated and aligned appearance associated with the severe shearing history. The microstructural characteristics and crystallography of the broached white layer suggest that it was essentially formed by adiabatic shear localization in which the dominant metallurgical process is rotational dynamic recrystallization based on mechanically-driven subgrain rotations. The grain refinement within the white layer led to an increase of the surface nano-hardness by 14% and a reduction in elastic modulus by nearly 10% compared to that of the bulk material. This is primarily due to the greatly increased volume fraction of grain boundaries, when the grain size was reduced down to the nanoscale.

  • 6.
    Chen, Zhe
    et al.
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, Faculty of Science & Engineering.
    Moverare, Johan
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, Faculty of Science & Engineering.
    Peng, Ru
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, Faculty of Science & Engineering.
    Johansson, Sten
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, Faculty of Science & Engineering.
    Gustafsson, David
    Siemens Industrial Turbomachinery AB, SE-61283 Finspång, Sweden.
    On the Conjoint Influence of Broaching and Heat Treatment on Bending Fatigue Behavior of Inconel 7182016In: Materials Science & Engineering: A, ISSN 0921-5093, E-ISSN 1873-4936, Vol. 671, p. 158-169Article in journal (Refereed)
    Abstract [en]

    In this study, the conjoint effect of a broaching operation, similar to that used for machining fir-tree slots on turbine discs, and subsequent heat treatments at 550 °C and 650 °C on the fatigue performance and corresponding crack initiation behavior of forged Inconel 718 has been investigated. Four-point bending fatigue tests were conducted under load control on specimens of two groups, i.e. a polished group and a broached group, with totally six different surface conditions. Compared to the as-polished specimens, a beneficial effect of the broaching operation was found on the fatigue life due to the high compressive residual stresses on the broached surface which transfer the fatigue crack initiation from surface to sub-surface regions. Introducing a heat treatment generally deteriorated the fatigue performance of the alloy because of the oxidation assisted crack initiation, while the reduction in fatigue life was found to be more remarkable for the broached specimens, in particular when heat treated at 650 °C, as the thermal impact also led to a great relaxation of the compressive residual stresses; the combined effect, together with the substantial anomalies created by broaching on the surface, such as cracked carbides and machining grooves, caused an increased propensity to surface cracking in fatigue and consequently a loss of the lifetime. Furthermore, it was found that the occurrence of surface recrystallization at elevated temperatures in machined Inconel 718 could lead to intergranular oxidation, creating micro-notches as preferable sites for the fatigue crack initiation.

  • 7.
    Deng, Dunyong
    et al.
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, Faculty of Science & Engineering.
    Moverare, Johan
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, Faculty of Science & Engineering.
    Peng, Ru Lin
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, Faculty of Science & Engineering.
    Söderberg, Hans
    Sandvik Machining Solutions AB, Sandviken, Sweden.
    Microstructure and Anisotropic Mechanical Properties of EBM Manufactued Inconel 718 and Effects of Post Heat Treatment2017In: Materials Science & Engineering: A, ISSN 0921-5093, E-ISSN 1873-4936, Vol. 693, p. 151-163Article in journal (Refereed)
    Abstract [en]

    Materials manufactured with electron beam melting (EBM) have different microstructures and properties to those manufactured using conventional manufacturing methods. A detailed study of the microstructures and mechanical properties of Inconel 718 manufactured with EBM was performed in both as-manufactured and heat-treated conditions. Different scanning strategies resulted in different microstructures: contour scanning led to heterogeneous grain morphologies and weak texture, while hatch scanning resulted in predominantly columnar grains and strong 〈001〉 building direction texture. Precipitates in the as-manufactured condition included γ′, γ″, δ  , TiN and NbC, among which considerable amounts of γ″ yielded relatively high hardness and strength. Strong texture, directionally aligned pores and columnar grains can lead to anisotropic mechanical properties when loaded in different directions. Heat treatments increased the strength and led to different δ precipitation behaviours depending on the solution temperatures, but did not remove the anisotropy. Ductility seemed to be not significantly affected by heat treatment, but instead by the NbC and defects inherited from manufacturing. The study thereby might provide the potential processing windows to tailor the microstructure and mechanical properties of EBM IN718.

  • 8.
    Deng, Dunyong
    et al.
    Linköping University, Department of Management and Engineering. Linköping University, Faculty of Science & Engineering.
    Peng, Ru
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, Faculty of Science & Engineering.
    Brodin, Håkan
    Siemens Ind Turbomachinery AB, Sweden.
    Moverare, Johan
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, Faculty of Science & Engineering.
    Microstructure and mechanical properties of Inconel 718 produced by selective laser melting: Sample orientation dependence and effects of post heat treatments2018In: Materials Science & Engineering: A, ISSN 0921-5093, E-ISSN 1873-4936, Vol. 713, p. 294-306Article in journal (Refereed)
    Abstract [en]

    Inconel 718 produced by selective laser melting (SLM) has been characterized with focus on the microstructure, the dependence of sample orientation on the mechanical properties and the effects of post heat treatments. The as-manufactured IN718 has a very fine cellular-dendritic structure with fine Laves phases precipitating in the interdendritic region, and electron backscatter diffraction (EBSD) analysis shows that both the vertically and horizontally built samples have relatively weak texture. The vertically built samples show lower tensile strength but higher ductility than the horizontally built samples, and the mechanism is shown to be partly due to the crystallographic feature but more importantly due to the different amount of residual stress and dislocations accumulated in these two kinds of samples. Applying heat treatments can significantly increase the strength while decrease the ductility correspondingly, and difference in yield strength between the vertically and horizontally built samples decreases with increasing the heat treatment temperatures, mainly due to the removal of residual stress and dislocations.

  • 9.
    Ekström, Thommy
    et al.
    AB Sandvik Hard Materials, Stockholm, Sweden.
    Käll, Per-Olov
    University of Stockholm, Sweden.
    Nygren, Mats
    University of Stockholm, Sweden.
    Olsson, Per-Olof
    University of Stockholm, Sweden.
    Mixed α- and β-(Si-Al-O-N) Materials with Yttria and Neodymia Additions1988In: Materials Science & Engineering: A, ISSN 0921-5093, E-ISSN 1873-4936, Vol. 105/106, p. 161-168Article in journal (Refereed)
    Abstract [en]

    A number of ceramic materials have been fabricated on a semipilot plant scale at different overall compositions in the (Y, Nd)---Al---O---N system at 177°C. Constant molar amounts of oxide mixtures of Y2O3: Nd2O3 in the ratios 100:0, 75:25, 50:50, 25:75 or 0:100 have been added. Dense materials were obtained for all compositions except those corresponding to mixed α- and β-(Si---Al---O---N) with higher α-(Si---Al---O---N) contents and high Nd2O3 contents. At the preparation temperature used in this study, the formation of an α-(Nd---Si---Al---O---N) seems prohibited and, thus, with increasing Nd2O3 content the amount of α-(Si---Al---O---N) decreased. The Nd2O3 added mainly formed crystalline intergranular phases such as the N-melilite phase, which increased in amount with increasing Nd2O3 in the starting mix. Hardness and indentation fracture toughness measurements were made and are discussed in relation to the phase composition and the microstructure. Some of the high Nd2O3 content Si---Al---O---N materials have as high fracture toughness values as the pure Y2O3 Si---Al---O---N materials do.

  • 10.
    Govik, Alexander
    et al.
    Linköping University, Department of Management and Engineering, Solid Mechanics. Linköping University, The Institute of Technology.
    Rentmeester, Rikard
    Saab AB, Linköping, Sweden.
    Nilsson, Larsgunnar
    Linköping University, Department of Management and Engineering, Solid Mechanics. Linköping University, The Institute of Technology.
    A study of the unloading behaviour of dual phase steel2014In: Materials Science & Engineering: A, ISSN 0921-5093, E-ISSN 1873-4936, Vol. 602, p. 119-126Article in journal (Refereed)
    Abstract [en]

    It is important to understand the strain recovery of a steel sheet in order to predict its springback behaviour. During strain recovery, the stress–strain relation is non-linear and the resulting unloading modulus is decreased. Moreover, the unloading modulus will degrade with increasing plastic pre-straining. This study aims at adding new knowledge on these phenomena and the mechanisms causing them. The unloading behaviour of the dual-phase steel DP600 is characterised experimentally and finite element (FE) simulations of a representative volume element (RVE) of the microstructure are performed. The initial stress and strain state of the micromechanical FE model is found by a simplified simulation of the annealing processes. It is observed from the experimental characterisation that the decrease of the initial stiffness of the unloading is the main reason for the degrading unloading modulus. Furthermore, the developed micromechanical FE model exhibits non-linear strain recovery due to local plasticity caused by interaction between the two phases.

  • 11.
    Jia, N
    et al.
    Key Laboratory for Anisotrooy and Testure of Materials Northeastern university, Shenyang, China.
    Peng, Ru
    Linköping University, The Institute of Technology. Linköping University, Department of Management and Engineering, Engineering Materials .
    Chai, G C
    Sandvik Materials Technology SFM Sandviken.
    Johansson, Sten
    Linköping University, Department of Management and Engineering, Engineering Materials . Linköping University, The Institute of Technology.
    Wang, Y D
    Key Laboratory for Anisotropy and Texture of Materials Northeastern university, Shenyang, China.
    Direct experimental mapping of microscale deformation heterogeneity in duplex stainless steel2008In: Materials Science & Engineering: A, ISSN 0921-5093, E-ISSN 1873-4936, Vol. 491, no 1-2, p. 425-433Article in journal (Refereed)
    Abstract [en]

    In situ tensile test has been performed with the electron back-scattering diffraction (EBSD) technique for characterizing the deformation heterogeneity at microscopic level of a duplex stainless steel consisting of austenite and ferrite. It was observed that, as deformation proceeded, the fraction of low-angle boundaries continuously increased and strain gradient developed at some grain boundaries and twin boundaries, as well as in the interior of some grains. The in situ experiments quantitatively captured the change of grain-orientation-dependent plastic behavior in respective phases and the strain partition between duplex phases as a function of applied strain. Using a visco-plastic self-consistent (VPSC) model incorporating the accommodation of micromechanical properties of grains with different orientations in two phases, the evolution of microstresses/microstrains at various length scales was simulated and discussed in detailed within the material undergoing plastic deformation. The experimental observations are well explained by the VPSC model. The present investigations provide the in-depth understanding of anisotropic micromechanical behaviors of the duplex steel. © 2008 Elsevier B.V. All rights reserved.

  • 12.
    Jinnestrand, Magnus
    et al.
    Linköping University, Department of Mechanical Engineering, Solid Mechanics. Linköping University, The Institute of Technology.
    Brodin, Håkan
    Linköping University, Department of Mechanical Engineering, Engineering Materials. Linköping University, The Institute of Technology.
    Crack initiation and propagation in air plasma sprayed thermal barrier coatings, testing and mathematical modelling of low cycle fatigue behaviour2004In: Materials Science & Engineering: A, ISSN 0921-5093, E-ISSN 1873-4936, Vol. 379, no 1-2, p. 45-57Article in journal (Refereed)
    Abstract [en]

    In the present paper failure mechanisms in air plasma sprayed thermal barrier coatings for land-based gas turbines have been studied. This has been done by finite element simulations and fractographic investigations of low cycle fatigue (LCF) tested material, here chosen as an 350 μm thick partially stabilised zirconia top coat (TC) together with a 150 μm thick Ni-Co-Cr-Al-Y bond coat (BC) on a nickel base substrate (Haynes 230). Both LCF testing, modelling results and fractographic investigations point in the same direction. An increased thickness of the thermally grown oxide (TGO) does decrease the LCF life of a coated structural alloy. Several points of crack initiation were found, in the TGO at the TC/BC interface, at the oxide network within the BC and at oxide inclusions between BC and substrate. During LCF tests the initiated cracks will grow radially into the substrate material. The behaviour is explained by increased TC/BC delamination stresses and changed oxidation behaviour with increased oxidation times.

  • 13.
    Johansson, Sten
    et al.
    Linköping University, Department of Mechanical Engineering, Engineering Materials. Linköping University, The Institute of Technology.
    Zeng, Xiaohu
    Linköping University, Department of Mechanical Engineering, Engineering Materials. Linköping University, The Institute of Technology.
    Andersson, Nils-Eric
    Linköping University, Department of Mechanical Engineering, Engineering Materials. Linköping University, The Institute of Technology.
    Peng, Ru
    Linköping University, Department of Mechanical Engineering, Engineering Materials. Linköping University, The Institute of Technology.
    Measurement of average texture of cold-rolled aluminium sheet by electron back-scattering diffraction: a comparison with neutron diffraction2001In: Materials Science & Engineering: A, ISSN 0921-5093, E-ISSN 1873-4936, Vol. 315, no 1-2, p. 129-135Article in journal (Refereed)
    Abstract [en]

         Measurements of the average texture on sheet of commercial pure aluminium have been performed using neutron diffraction and electron back-scattering diffraction (EBSD). Orientation distribution function maps have been calculated and compared. The results show a good correspondence provided that the data from the EBSD measurements are corrected according to a texture index versus inverted number of measurement procedure. Most errors are probably related to differences in investigated volume and calculation technique and to the fact that the microstructure was difficult for EBSD measurements.

  • 14.
    Kanesund, Jan
    et al.
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, The Institute of Technology.
    Moverare, Johan
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, The Institute of Technology.
    Johansson, Sten
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, The Institute of Technology.
    Deformation and damage mechanisms in IN792 during thermomechanical fatigue2011In: Materials Science & Engineering: A, ISSN 0921-5093, E-ISSN 1873-4936, Vol. 528, no 13-14, p. 4658-4668Article in journal (Refereed)
    Abstract [en]

    The deformation and damage mechanisms arising during thermomechanical fatigue (TMF) of the polycrystallinesuperalloy IN792 have been investigated. The TMF cycles used in this study are in-phase(IP) and out-of-phase (OP). The minimum temperature used in all TMF-tests is 100 ◦C while the maximumtemperature is 500 or 750 ◦C in the IP TMF-tests and 750, 850 or 950 ◦C in the OP TMF-tests. Themajority of the cracks are transcrystalline, except for the IP TMF-test at 750 ◦C, where some tendencyto intercrystalline crack growth can be seen. In all tests, the cracks were initiated and propagated inlocations where deformation structures such as deformation bands have formed in the material. In thetemperature interval 750–850 ◦C, twins were formed in both IP and OP TMF-tests and this behaviouris observed to be further enhanced close to a crack. Twins are to a significantly lesser extent observedfor tests with a lower (500 ◦C) and a higher (950 ◦C) maximum temperature. Recrystallization at grainboundaries, around particles and within the deformation structures have occurred in the OP TMF-testswith a maximum temperature of 850 and 950 ◦C and this is more apparent for the higher temperature.Void formation is frequently observed in the recrystallized areas even for the case of compressive stressesat high temperature.

  • 15.
    Larsson, Cecilia
    et al.
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, The Institute of Technology.
    Holden, T.M.
    Los Alamos National Laboratory, Los Alamos, USA.
    Bourke, M.A.M.
    Los Alamos National Laboratory, Los Alamos, USA.
    Stout, M.
    Los Alamos National Laboratory, Los Alamos, USA.
    Teague, J.
    Los Alamos National Laboratory, Los Alamos, USA.
    Lindgren, L.-E.
    Div. Comp. Aided Design, Luleå University of Technology and Dalarna University, Luleå, Sweden.
    Measurement and modeling of residual stress in a welded Haynes® 25 cylinder2005In: Materials Science & Engineering: A, ISSN 0921-5093, E-ISSN 1873-4936, Vol. 399, no 1-2, p. 49-57Article in journal (Refereed)
    Abstract [en]

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

  • 16.
    Larsson, Cecilia
    et al.
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, The Institute of Technology.
    Odén, Magnus
    Linköping University, Department of Mechanical Engineering, Engineering Materials. Linköping University, The Institute of Technology.
    Hardness profile measurements in functionally graded WC–Co composites2004In: Materials Science & Engineering: A, ISSN 0921-5093, E-ISSN 1873-4936, Vol. 382, no 1-2, p. 141-149Article in journal (Refereed)
    Abstract [en]

    Micro- and nanoindentation were used to determine hardness as a function of depth in two functionally graded WC–Co composites. The gradients were continuous (extended over ∼70 and ∼40 μm, respectively) and consisted of varying WC and Co phase volume fractions. Five comparable homogeneous samples with different Co contents and different average WC grain sizes were also used for direct comparison. A relationship between hardness and Co content was established for both the graded and the homogeneous samples wherein the hardness decreased with increasing Co content. The magnitude of the hardness was the same (for a given Co content) for the functionally graded and the homogeneous materials. The hardness measurements were also correlated with X-ray diffraction studies of thermal residual stresses and the absence of any major influence explained. It is generally concluded that the hardness values are dominated by the local Co content. Additionally, the examination of surface cracks around indents suggests that compositional gradients in WC–Co composites offer increased toughness.

  • 17.
    Moverare, Johan
    et al.
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, The Institute of Technology.
    Gustafsson, David
    Linköping University, Department of Management and Engineering, Solid Mechanics. Linköping University, The Institute of Technology.
    Hold-time effect on the thermo-mechanical fatigue crack growth behaviour of Inconel 7182011In: Materials Science & Engineering: A, ISSN 0921-5093, E-ISSN 1873-4936, Vol. 528, no 29-30, p. 8660-8670Article in journal (Refereed)
    Abstract [en]

    In-phase TMF crack growth testing with different lengths of the hold time at the maximum temperature of 550 °C has been conducted on Inconel 718 specimens. Focus has been on establishing a method for TMF crack growth testing and investigating the effect of high temperature hold times on the TMF crack growth of the material. The tests are compared to isothermal crack propagation tests and show good correlation. It is concluded that the controlling effect of the crack growth is an embrittlement of the material. This embrittlement is related to the concept of a damaged zone active in front of the crack tip. The size of this damaged zone will control the crack propagation rate and therefore it does not matter if the load is cycled under isothermal or TMF conditions.

  • 18.
    Moverare, Johan
    et al.
    Linköping University, Department of Management and Engineering, Engineering Materials . Linköping University, The Institute of Technology.
    Johansson, Sten
    Linköping University, Department of Management and Engineering, Engineering Materials . Linköping University, The Institute of Technology.
    Damage mechanisms of a high-Cr single crystal superalloy during thermomechanical fatigue2010In: Materials Science & Engineering: A, ISSN 0921-5093, E-ISSN 1873-4936, Vol. 527, no 3, p. 553-558Article in journal (Refereed)
    Abstract [en]

    The deformation and damage mechanisms arising during thermomechanical fatigue of a high-Cr single crystal superalloy have been investigated and a completely new failure mechanism involving recrystallization and oxidation has been discovered. The primary deformation mechanism is slip along the {1 1 1} planes. The deformation is highly localized to a number of bands, where recrystallization eventually occurs during the thermomechanical fatigue process. When the final failure occurs along these recrystallized bands it is accompanied by the formation of voids due to the presence of grain boundaries. The damage process is further enhanced by oxidation, since recrystallization occurs more easily in the γ′ depleted zone under the oxide layer.

  • 19.
    Moverare, Johan
    et al.
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, The Institute of Technology.
    Leijon, Gunnar
    SWEREA Kimab AB, Stockholm, Sweden.
    Brodin, Håkan
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, The Institute of Technology.
    Palmert, Frans
    Siemens Industrial Turbomachinery AB, Finspång, Sweden.
    Effect of SO2 and water vapour on the low-cycle fatigue properties of nickel-base superalloys at elevated temperature2013In: Materials Science & Engineering: A, ISSN 0921-5093, E-ISSN 1873-4936, Vol. 564, p. 107-115Article in journal (Refereed)
    Abstract [en]

    In this study the effect of SO2+water vapour on strain controlled low cycle fatigue resistance of three different nickel based superalloys has been studied at 450 °C and 550 °C. A negative effect was found on both the crack initiation and crack propagation process. The effect increases with increasing temperature and is likely to be influenced by both the chemical composition and the grain size of the material. In general the negative effect decreases with decreasing strain range even if this means that the total exposure time increases. This is explained by the importance of the protective oxide scale on the specimen surface, which is more likely to crack when the strain range increases. When the oxide scale cracks, preferably at the grain boundaries, oxidation can proceed into the material, causing preferable crack initiation sites and reduced fatigue resistance.

  • 20.
    Moverare, Johan
    et al.
    Linköping University, Department of Mechanical Engineering, Engineering Materials. Linköping University, The Institute of Technology.
    Odén, Magnus
    Linköping University, Department of Mechanical Engineering, Engineering Materials. Linköping University, The Institute of Technology.
    Deformation behaviour of a prestrained duplex stainless steel2002In: Materials Science & Engineering: A, ISSN 0921-5093, E-ISSN 1873-4936, Vol. 337, no 1-2, p. 25-38Article in journal (Refereed)
    Abstract [en]

    The anisotropic flow behaviour due to a change in strain path during uniaxial deformation of a duplex stainless steel has been investigated. The anisotropic flow behaviour of the as-received material could be predicted from the crystallographic texture. However, it was found that prestraining introduces a transient work hardening behaviour during the second stage deformation, which causes an anisotropic flow behaviour immediately after yielding that cannot be described by the crystallographic texture. Samples subjected to a coaxial second stage deformation show a small increase in flow stress and similar work hardening rate as in the monotonic loading. Samples subjected to noncoaxial second stage deformation show a pronounced transient stage characterised by early yielding and a high work hardening rate in the first part of the transient stage. Beyond the earliest stage of deformation a higher flow stress and a lower work hardening rate compared to monotonic loading is observed for the noncoaxial samples. The transient phenomena are discussed based on the measured internal stresses and the differences in dislocation structures in the two different phases.

  • 21.
    Papachristos, V.D.
    et al.
    Laboratory of Physical Metallurgy, Natl. Tech. Univ. Athens, 157 80 Z., Athens, Greece.
    Panagopoulos, C.N.
    Laboratory of Physical Metallurgy, Natl. Tech. Univ. Athens, 157 80 Z., Athens, Greece.
    Wahlstrom, U.
    Industrial Microelectronics Center, 581 83, Linkoping, Sweden.
    Christoffersen, L.W.
    Technical University of Denmark, 2800, Lyngby, Denmark.
    Leisner, P.
    Industrial Microelectronics Center, 581 83, Linkoping, Sweden.
    Effect of annealing on the structure and hardness of Ni-P-W multilayered alloy coatings produced by pulse plating2000In: Materials Science & Engineering: A, ISSN 0921-5093, E-ISSN 1873-4936, Vol. 279, no 1-2, p. 217-230Article in journal (Refereed)
    Abstract [en]

    Ni-P-W multilayered alloy coatings were deposited on copper foils by pulse plating, using a rotating cylinder electrode. They consisted of layers of high (Ni-5 wt.% P-45 wt.% W) and low (Ni-8 wt.% P-15 wt.% W) W content. The wavelengths studied were 8, 40 and 400 nm and the total thickness of the coatings was approximately 25 µm. The multilayered coatings were annealed in the temperature range between 200 and 800°C and the effect of annealing on their structure was studied by using X-ray diffraction, cross-sectional transmission electron microscopy equipped with selected area electron diffraction facility, and differential thermal analysis. The initially amorphous multilayered coatings crystallise in steps as the annealing temperature increases (first the low-W crystallise layers and then the high-W layers), and the layered structure is lost around 600°C. The main crystalline phases formed during annealing are Ni-W solid solution and Ni3P. The wavelength of the coatings seems to affect the onset temperature of the crystallisation processes. The hardness of the coatings initially increases reaching a maximum in the 500-600°C range, and then decreases as the annealing temperature increases. (C) 2000 Elsevier Science S.A. All rights reserved.Ni-P-W multilayered alloy coatings were deposited on copper foils by pulse plating, using a rotating cylinder electrode. They consisted of layers of high (Ni-5 wt.% P-45 wt.% W) and low (Ni-8 wt.% P-15 wt.% W) W content. The wavelengths studied were 8, 40 and 400 nm and the total thickness of the coatings was approximately 25 µm. The multilayered coatings were annealed in the temperature range between 200 and 800°C and the effect of annealing on their structure was studied by using X-ray diffraction, cross-sectional transmission electron microscopy equipped with selected area electron diffraction facility, and differential thermal analysis. The initially amorphous multilayered coatings crystallise in steps as the annealing temperature increases (first the low-W crystallise layers and then the high-W layers), and the layered structure is lost around 600°C. The main crystalline phases formed during annealing are Ni-W solid solution and Ni3P. The wavelength of the coatings seems to affect the onset temperature of the crystallisation processes. The hardness of the coatings initially increases reaching a maximum in the 500-600°C range, and then decreases as the annealing temperature increases.

  • 22.
    Peng, Ru
    et al.
    Linköping University, The Institute of Technology. Linköping University, Department of Mechanical Engineering, Engineering Materials.
    Odén, Magnus
    Linköping University, The Institute of Technology. Linköping University, Department of Mechanical Engineering, Engineering Materials.
    Wang, Y D
    Studsvik Neutron Research Lab Uppsala University.
    Johansson, Sten
    Linköping University, The Institute of Technology. Linköping University, Department of Mechanical Engineering, Engineering Materials.
    Intergranular strains and plastic deformation of an austenitic stainless steel2002In: Materials Science & Engineering: A, ISSN 0921-5093, E-ISSN 1873-4936, Vol. 334, no 1-2, p. 215-222Article in journal (Refereed)
    Abstract [en]

    Intergranular strains due to tensile plastic deformation were investigated in a sheet material of austenitic stainless steel. The objective was to study the development of residual intergranular strains in samples unloaded from the intermediate and large plastic deformation regimes for which few theoretical and experimental studies were available. By using neutron diffraction, residual lattice strain distribution as a function of sample direction was mapped for a number of crystallographic planes. Deformation microstructures were examined by both transmission electron microscopy and the electron back scattering pattern technique. Residual intergranular strains were observed in samples deformed significantly beyond the elastic limit and the strains varied with sample directions as well as the amount of applied plastic strain. In addition, a different tendency of intergranular strain evolution was observed after large plastic deformation, which could be attributed to the change of dominant plastic deformation mode from slip to mechanical twinning. The results are discussed based on the observed deformation microstructure studies. ⌐ 2002 Elsevier Science B.V. All rights reserved.

  • 23.
    Polák, Jaroslav
    et al.
    Institute of Physics of Materials, Academy of Sciences of Czech Republic, Brno.
    Petrás, Roman
    Institute of Physics of Materials, Academy of Sciences of the Czech Republic, Brno.
    Chai, Guocai
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, Faculty of Science & Engineering.
    Skorik, Viktor
    Institute of Physics of Materials, Academy of Sciences of the Czech Republic, Brno.
    Surface Profile Evolution adn Fatigue Crack Initiation in Sanicro 25 Steel at Room Temperature2016In: Materials Science & Engineering: A, ISSN 0921-5093, E-ISSN 1873-4936, Vol. 658, p. 221-228Article in journal (Refereed)
    Abstract [en]

    Evolution of the surface profile in room temperature cyclic loading has been studied in high alloy austenitic Sanicro 25 stainless steel. The localization of the cyclic plastic strain into persistent slip bands in the volume of the material leads to the formation of the specific surface relief in the form of persistent slip markings (PSMs) consisting of extrusions and intrusions. Evolution of the shape of PSMs was studied during interruption of cycling using SEM and FIB techniques. Three-dimensional information about the PSMs profiles was obtained. The profiles of both extrusions and intrusions and their evolution during cyclic loading were assessed. Generally extrusions grow, intrusions deepen and fatigue cracks initiate from the tip of the deepest intrusions. The experimental observations were compared and discussed in relation to existing physical models of surface relief formation and fatigue crack initiation.

  • 24. Polák, Jaroslav
    et al.
    Petrás, Romas
    Institute of Physics of Materials, Academy of Sciences of the Czech Republic, Brno.
    Heczko, Milan
    Institute of Physics of Materials, Academy of Sciences of the Czech Republic, Brno.
    Kubena, Ivo
    Institute of Physics of Materials, Academy of Sciences of the Czech Republic, Brno.
    Kruml, Tomás
    Institute of Physics of Materials, Academy of Sciences of the Czech Republic, Brno.
    Chai, Guocai
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, Faculty of Science & Engineering.
    Low Cycle Fatigue Behavior of Sanicro25 Steel at Room and at Elevated Temperature2014In: Materials Science & Engineering: A, ISSN 0921-5093, E-ISSN 1873-4936, Vol. 615, p. 175-182Article in journal (Refereed)
    Abstract [en]

    Austenitic heat resistant Sanicro 25 steel developed for high temperature applications in power generation industry has been subjected to strain controlled low cycle fatigue tests at ambient and at elevated temperature in a wide interval of strain amplitudes. Fatigue hardening/softening curves, cyclic stress–strain curves and fatigue life curves were evaluated at room temperature and at 700 °C. The internal dislocation structures of the material at room and at elevated temperature were studied using transmission electron microscopy. High resolution surface observations and FIB cuts revealed early damage at room temperature in the form of persistent slip bands and at elevated temperature as oxidized grain boundary cracks. Dislocation arrangement study and surface observations were used to identify the cyclic slip localization and to discuss the fatigue softening/hardening behavior and the temperature dependence of the fatigue life.

  • 25. Rester, M.
    et al.
    Neidhardt, Jörg
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics.
    Eklund, Per
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics.
    Emmerlich, Jens
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics.
    Ljungcrantz, H.
    Hultman, Lars
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics.
    Mitterer, C.
    Annealing studies of nanocomposite Ti-Si-C thin films with respect to phase stability and tribological performance2006In: Materials Science & Engineering: A, ISSN 0921-5093, E-ISSN 1873-4936, Vol. 429, no 1-2, p. 90-95Article in journal (Refereed)
    Abstract [en]

    Nanocomposite Ti-Si-C thin films were deposited by dc magnetron sputtering from a Ti3SiC2 target onto Si(1 0 0) and high-speed steel substrates at 300 °C. The as-deposited films consisted of nanocrystalline (nc-) TiCx and amorphous (a-) SiCx, as determined by X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). Annealing in vacuum up to 1450 °C resulted in improved crystallinity and a decreased volume fraction of the amorphous phase. Additionally, differential scanning calorimetry (DSC) was used to monitor heat flows connected to the respective reactions in the material, where a broad exothermic peak attributed to grain growth of crystalline TiCx appeared, while an exothermic reaction related to the formation of Ti3SiC2 was not detected. Tribological testing in a ball-on-disk setup was conducted at room temperature, 500 and 700 °C against an alumina counterpart. The room temperature measurement resulted in a coefficient of friction value of 0.8, at elevated temperatures the coefficient of friction decreased to 0.4. © 2006 Elsevier B.V. All rights reserved.

  • 26.
    Saarimäki, Jonas
    et al.
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, Faculty of Science & Engineering.
    Hörnqvist Colliander, Magnus
    Dept of Applied Physics, Chalmers University of Technology, Gothenburg and GKN Aerospace engine Systems, R&T Centre, Trollhättan.
    Moverare, Johan
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, Faculty of Science & Engineering.
    Anisotropy Effects During Dwell-fatigue Caused by δ-phase Orientation in Forged Inconel 7182017In: Materials Science & Engineering: A, ISSN 0921-5093, E-ISSN 1873-4936, no 692, p. 174-181Article in journal (Refereed)
    Abstract [en]

    Inconel 718 is a commonly used superalloy for turbine discs in the gas turbine industry. Turbine discs are often subjected to dwell-fatigue as a result of long constant load cycles. The effect of anisotropy on dwell-fatigue cracking in forged turbine discs have not yet been thoroughly investigated. Crack propagation behaviour was characterised using compact tension (CT) samples cut in different orientations from a real turbine disc forging. Samples were also cut in two different thicknesses in order to investigate the influence of plane strain and plane stress condition on the crack propagation rates. The samples were subjected to dwell-fatigue tests at 550 °C with 90 s or 2160 s dwell-times at maximum load. Microstructure characterisation was done using scanning electron microscopy (SEM) techniques such as electron channelling contrast imaging (ECCI), electron backscatter diffraction (EBSD), and light optical microscopy (LOM). The forged alloy exhibits strong anisotropic behaviour caused by the non-random δ-phase orientation. When δ-phases were oriented perpendicular compared to parallel to the loading direction, the crack growth rates were approximately ten times faster. Crack growth occurred preferably in the interface between the γ-matrix and the δ-phase.

    The full text will be freely available from 2019-03-20 10:52
  • 27.
    Saarimäki, Jonas
    et al.
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, Faculty of Science & Engineering.
    Lundberg, Mattias
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, Faculty of Science & Engineering.
    Brodin, Håkan
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, Faculty of Science & Engineering. Siemens Ind Turbomachinery AB, Sweden.
    Moverare, Johan
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, Faculty of Science & Engineering.
    Dwell-fatigue crack propagation in additive manufactured Hastelloy X2018In: Materials Science & Engineering: A, ISSN 0921-5093, E-ISSN 1873-4936, Vol. 722, p. 30-36Article in journal (Refereed)
    Abstract [en]

    Additively manufactured Hastelloy X by laser-powderbed fusion is a superalloy used in for example burners and non-rotating parts in gas turbines. Turbines are often subjected to dwell-fatigue as a result of an operating profile including load cycles with long constant power output. The effect of building direction and heat treatments on dwell-fatigue crack propagation in additively manufactured Hastelloy X has not yet been thoroughly investigated. Crack propagation behaviour was characterized using compact tension samples cut from as-built and heat treated material blocks. Samples were machine with the notch parallel and perpendicular to the building direction enabling the investigation of building direction on crack behaviour and crack propagation rates. The samples were subjected to dwell-fatigue tests at 700 degrees C with 90 s or 2160 s dwell-times at maximum load. Microstructural characterization was conducted using light optical microscopy and scanning electron microscopy techniques such as electron channelling contrast imaging and electron backscatter diffraction. The additively manufactured alloy exhibits anisotropic behaviour caused by the directionally solidified microstructure. Cracks propagated intergranularly and preferably through streaks of topologically dose-packed phases.

  • 28.
    Segersäll, Mikael
    et al.
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, The Institute of Technology.
    Leidermark, Daniel
    Linköping University, Department of Management and Engineering, Solid Mechanics. Linköping University, The Institute of Technology.
    Moverare, Johan
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, The Institute of Technology.
    Influence of crystal orientation on the thermomechanical fatigue behaviour in a single-crystal superalloy2015In: Materials Science & Engineering: A, ISSN 0921-5093, E-ISSN 1873-4936, Vol. 623, no 19, p. 68-77Article in journal (Refereed)
    Abstract [en]

    In this study, the influuence from crystal orientation on the thermomehanical fatigue (TMF) behaviour of the recently developed single-rystal superalloy STAL-15 is considered, both from an experimental and a nite element (FE) perspective. Experimental results show that there is a strong inuence from the elastic stiffness, with respect to the loading direction, on the TMF life. However, the results also indicate that the number of active slip planes duringdeformation inuence the TMF life, where specimens with a higher number of active slip planes are favoured compared to specimens with fewer active slip planes. The higher number of active slip planes results in a more widespread deformation compared to a more conentrated deformation when only one slip plane is active. Deformation bands with smeared and elongated  γ-precipitates together with deformation twinning were found to be major deformation mechanisms, where the twins primarily were observed in specimens with several active slip planes. From an FE-perspective, therystal orientation with respect to the loading direction is quantied and adopted into a framework which makes it possible to describe the internal crystallographic arrangement and its entities in a material model. Further, a material model which incorporates the crystalorientation is able to predict the number of slip planes observed from microstructural observations, as well as the elasticstiness of the material with respect to the loading direction.

  • 29.
    Seifeddine, Salem
    et al.
    Linköping University, The Institute of Technology. Linköping University, Department of Management and Engineering, Engineering Materials .
    Johansson, Sten
    Linköping University, The Institute of Technology. Linköping University, Department of Management and Engineering, Engineering Materials .
    Svensson, Ingvar L
    Komponentteknologi Ingenjörshögskolan i Jönköping.
    The influence of cooling rate and manganese content on the beta-Al5FeSi phase formation and formation and mechanical properties of Al-Si based alloys2008In: Materials Science & Engineering: A, ISSN 0921-5093, E-ISSN 1873-4936, Vol. 490, no 39845, p. 385-390Article in journal (Refereed)
    Abstract [en]

    The present study investigates the influence of manganese level and cooling rate on the formation of iron compounds and mechanical properties of Al–9%Si alloys containing 0.3%Fe. It has been established that high cooling rates and Mn additions are not able to totally nullify the formation of β-Al5FeSi-needles onto α-Al15(Fe,Mn)3Si2-Chinese scripts even at Mn:Fe ratio of 2:1, but produces improvement in tensile strength unlike the ductility which suffers a loss with the increment of Mn concentrations.

  • 30.
    Semchuk, O. Yu.
    et al.
    Institute of Surface Chemistry NAS of Ukraine.
    Grechko, L. G.
    Institute of Surface Chemistry NAS of Ukraine.
    Bila, R.V.
    Institute of Surface Chemistry NAS of Ukraine.
    Willander, Magnus
    bChalmers University of Technology and Goteborg University.
    Karlsteen, M.
    bChalmers University of Technology and Goteborg University.
    Features of transport phenomenas in magnetic semiconductors with laser-induced periodic nanostructures2007In: Materials Science & Engineering: A, ISSN 0921-5093, E-ISSN 1873-4936, Vol. 27, no 5-8, p. 1360-1363Article in journal (Refereed)
    Abstract [en]

    The mechanisms of formation of the laser-induced periodic surface and bulk nanostructures in magnetic semiconductors are considered. Their influence on transport phenomena in ferromagnetic semiconductors (FMSC) is investigated. It is shown that under action of laser beams (LB) a laser-induced periodic nanostructures — gratings of the electron and magnon temperatures, electron concentration and electric fields arises in FMSC. It is determined, that the illuminating of an external surface of the FMSC by several LB results in an emerging new effect — appearance of a dropping site on the voltage-current characteristic (VCC) of the FMSC with the static laser-induced periodic nanostructures. This effect can only be observed for the carrier concentration n ≥ 1018 cm−3, since for smaller concentration the contribution of an additional current caused by the presence of the laser-induced periodic nanostructures will be insignificant.

  • 31.
    Si, Xiaoyang
    et al.
    Chinese Academic Science, Peoples R China; Shanghai University, Peoples R China.
    Li, Mian
    Chinese Academic Science, Peoples R China; University of Chinese Academic Science, Peoples R China.
    Chen, Fanyan
    Chinese Academic Science, Peoples R China.
    Eklund, Per
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, Faculty of Science & Engineering.
    Xue, Jianming
    Peking University, Peoples R China.
    Huang, Feng
    Chinese Academic Science, Peoples R China.
    Du, Shiyu
    Chinese Academic Science, Peoples R China.
    Huang, Qing
    Chinese Academic Science, Peoples R China.
    Effect of carbide interlayers on the microstructure and properties of graphene-nanoplatelet-reinforced copper matrix composites2017In: Materials Science & Engineering: A, ISSN 0921-5093, E-ISSN 1873-4936, Vol. 708, p. 311-318Article in journal (Refereed)
    Abstract [en]

    Copper matrix composites reinforced with carbide-coated graphene nanoplatelets (GNPs) were investigated in order to understand the role of the interlayers on the thermal, electrical, mechanical and electro-tribological properties of the composites. The TiC or VC coatings were formed in situ on the two sides of GNPs through a controllable reaction in molten salts. Compared with bare GNPs composites, the bonding between the GNPs and copper was improved. Accordingly, the tensile strength and the fracture elongation of Cu/GNPs composites with an interlayer were enhanced by strengthened interfacial bonding. Furthermore, the wear resistance of Cu/GNPs composites was remarkably improved.

    The full text will be freely available from 2019-10-05 10:23
  • 32.
    Yang, J.
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Nanostructured Materials. Linköping University, Faculty of Science & Engineering. University of Politecn Cataluna, Spain; Pol Ind Les Fallulles, Spain.
    Odén, Magnus
    Linköping University, Department of Physics, Chemistry and Biology, Nanostructured Materials. Linköping University, Faculty of Science & Engineering.
    Johansson-Joesaar, M. P.
    Linköping University, Department of Physics, Chemistry and Biology, Nanostructured Materials. Linköping University, Faculty of Science & Engineering. SECO Tools AB, Sweden.
    Esteve, J.
    University of Barcelona, Spain.
    Llanes, L.
    University of Politecn Cataluna, Spain; University of Politecn Cataluna, Spain.
    Mechanical strength of ground WC-Co cemented carbides after coating deposition2017In: Materials Science & Engineering: A, ISSN 0921-5093, E-ISSN 1873-4936, Vol. 689, p. 72-77Article in journal (Refereed)
    Abstract [en]

    Manufacturing of hardmetal tools often involves surface grinding, ion etching and final coating. Each stage throughout the manufacturing chain introduces surface integrity changes which may be critical for defining the final mechanical behavior of the coated tools. Within this context, an experimental test program has been developed to assess the influence of a coating (TiN) deposition on surface integrity and transverse rupture strength of a previously ground fine-grained WC-Co grade substrate. Four different substrate surface finish conditions (prior to ion etching and coating) were evaluated: as sintered (AS), ground (G), polished (P), and ground plus high temperature annealing (GTO. Surface integrity and fracture resistance characterization, complemented with a detailed fractographic analysis, were performed on both uncoated and coated samples. Results show that the surface integrity after grinding has been partly modified during the ion etching and film deposition processes, particularly in terms of a reduced compressive residual stress state at the substrate surface level. Consequently, the grinding induced strength enhancement in hardmetals is reduced for coated specimens. Main reason behind it is the change of nature, location and stress state acting on critical flaw: from processing defects existing at the subsurface (uncoated G specimens) to grinding-induced microcracks located close to the interface between coating and substrate, but within the subsurface of the latter (coated G specimens). This is not the case for AS and P conditions, where flexural strength does not change a result of ion etching and coating. Finally, fracture resistance increases slightly for GTT specimens after coating process, possibly caused by a beneficial effect of the deposited film on the residual stress state at the surface.

  • 33.
    Zhou, Nian
    et al.
    Dept of Materials Science, Dalarna University, Sweden.
    Pettersson, Rachel
    KTH och Jernkontoret, Stockholm.
    Peng, Ru Lin
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, Faculty of Science & Engineering.
    Schönning, Mikael
    Corrosion Dept, Avesta Research Centre, Outokumpu Stainless AB, Avesta.
    Effect of Surface Grinding on Chloride Induced SCC of 304L2016In: Materials Science & Engineering: A, ISSN 0921-5093, E-ISSN 1873-4936, Vol. 658, p. 50-59Article in journal (Refereed)
    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.

1 - 33 of 33
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