Analysis of Sintering Residual Stress and Microscopic Stress/Strain under Uniaxial Tension in WC-Co Hardmetal

Abstract

Analyses have been made on the sintering residual stress and the microscopic stress/strain under uniaxial tension in WC-Co hardmetal with a mechanical model of two-phase sintered materials, as proposed in a previous paper. The cooling process in sintering was simulated by introducing thermal stress into the mechanical model. The results obtained on the sintering residual stress in WC-grain and Co-binder agree well with the experimental values obtained by the X-ray diffraction method given in a reference. The analyses of the microscopic stress/strain in WC-grain and Co-binder were made under two initial conditions ; one with no sintering residual stress and the other with sintering residual stress. The results of the calculation have shown that the sintering residual stress has no influence on the maximum values of microscopic stress in the WC-grain and Co-binder, but it has influence on the plastic deformation in the Co-binder. The variation of the transverse rupture strength of WC-Co hardmetal, as a function of Co volume fraction V_Co, is explained based on two kinds of fracture criteria, one of which is effective, depending on the value of V_Co ; the transverse rupture strength is controlled by flaw size in the lower V_Co region, and by microscopic stress/strain in the higher V_Co region.