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تسجيل مستخدم جديدMicropillar compression of single crystal tungsten carbide, Part 1: temperature and orientation dependence of deformation behaviour
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Tungsten carbide cobalt hardmetals are commonly used as cutting tools subject to high operation temperature and pressures, where the mechanical performance of the tungsten carbide phase affects the wear and lifetime of the material. In this study, the mechanical behaviour of the isolated tungsten carbide (WC) phase was investigated using single crystal micropillar compression. Micropillars 1-5 ${mu}$m in diameter, in two crystal orientations, were fabricated using focused ion beam (FIB) machining and subsequently compressed between room temperature and 600 {deg}C. The activated plastic deformation mechanisms were strongly anisotropic and weakly temperature dependent. The flow stresses of basal-oriented pillars were about three times higher than the prismatic pillars, and pillars of both orientations soften slightly with increasing temperature. The basal pillars tended to deform by either unstable cracking or unstable yield, whereas the prismatic pillars deformed by slip-mediated cracking. However, the active deformation mechanisms were also sensitive to pillar size and shape. Slip trace analysis of the deformed pillars showed that {10-10} prismatic planes were the dominant slip plane in WC. Basal slip was also identified as a secondary slip system, activated at high temperatures.
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The plastic deformation mechanisms of tungsten carbide at room and elevated temperatures influence the wear and fracture properties of WC-Co hardmetal composite materials. Although the active slip planes and residual defect populations of room-temper
ature deformed WC have been previously characterised, the relationship between the residual defect structures, including glissile and sessile dislocations and stacking faults, and the active slip modes, which produce slip traces, is not yet clear. Part 1 of this study showed that {10-10} was the primary slip plane at all temperatures and orientations. In the present work, Part 2, crystallographic lattice reorientations of deformed WC micropillar mid-sections were mapped using focused ion beam (FIB) cross-sectioning and electron backscatter diffraction (EBSD). Lattice reorientation axis analysis has been used to discriminate <a> prismatic slip from multiple <c+a> prismatic slip in WC, enabling defect-scale deformation mechanisms to be distinguished, and their contribution to plastic deformation to be assessed, independently of TEM residual defect analysis. In prismatic-oriented pillars, deformation was primarily accommodated by cooperative multiple slip of <c+a> defects at room temperature, and by <a> dislocations at 600 {deg}C. In near-basal oriented pillars, the total slip direction was along <c>. The degree of lattice rotation and plastic buckling in the deformed basal pillar could be explained by prismatic slip constrained by the indenter face and pillar base.
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