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Several finite element models of the morphology of WC-10 wt.% Co were employed to reproduce the build-up of thermal residual stresses as well as the phase specific strain during loading-unloading in compression. The different models differ only in their geometry of the interpenetrating skeletons of WC and Co. They all respect the given volume proportion of each phase. Thermoelasticity is considered for the brittle WC, while also plasticity is included to model the Co binder phase. We compare the predictions of our FEM models with phase specific strain measurements performed by in-situ neutron diffraction and discuss the model validation. (C) 2014 Elsevier Ltd. All rights reserved.

The interaction of uniaxial applied stress with the thermal residual stress state in a WC–10 wt.% Ni cemented carbide composite was studied. A previously proposed model, based on results for uniaxial compressive loading, explains the observed asymmetric relaxation of the pre-existing thermal residual stress. This model predicts that the sense of the asymmetry would reverse in the case of tensile loading. The main purpose of the present work was to test this prediction. The reversal of signs was observed. The addition of tensile data has enabled the role of thermal residual stress on stress–strain response to be further elucidated. More complex behavior is observed with respect to the response of the variance in residual stresses, as measured by changes in diffraction peak breadths.

The interaction of uniaxial compressive load and thermal residual stress was measured in a WC–10 wt.% (16 vol.%) Ni cemented carbide composite using neutron diffraction. Loading was from 0 to −2500 MPa in increments of 250 MPa, and measurements were made in situ during load–unload cycles 1, 2, 3, 10, 25, 50 and 100. Plasticity is observed in the Ni from the lowest levels of applied load, leading to continuous curvature of the WC–Ni stress–strain curves, and is believed to be a significant contribution to the composite’s toughness. It is due to interaction between local extremes of the thermal residual microstress with the applied macrostress and leads to anisotropic relaxation of the thermal residual stress. Strain distribution and plasticity were observed through peak breadths. Although the initially strong hysteresis is reduced as the cycles increase, there are still changes taking place after 100 cycles.

The in-situ strain response of WC-Ni cemented carbides (5, 10, and 20 wt pct Ni) to uniaxial compressive load was measured using neutron diffraction. Strain was measured in both phases parallel and transverse to the loading axis of cylindrical samples. Plasticity is observed in the Ni binder from the lowest levels of applied load. The plasticity occurs locally in the Ni phase, on the scale of the microstructure, and leads to continuous curvature of the WC-Ni stress-strain curves and significant toughness of the material. The plasticity results from the interaction of the thermal residual microstresses created during sample production with the applied macrostress. It also leads to anisotropic relaxation of the initial residual stress and the creation of a residual stress state with cylindrical symmetry in the material. This process was observed over three load-unload cycles. Analysis enables phase-specific stress strain curves to be constructed. Finally, strain distributions were observed through peak breadth responses.

The strain response of WC and Ni in WC–Ni cemented carbide composites (5, 10 and 20 wt.% Ni) was studied under uniaxial compressive load to � 2000 MPa using neutron diffraction. Measurements of elastic strain were made simultaneously in the axial and transverse directions of the samples, for both phases. Thermal residual stresses (TRS) were also measured, before and after loading. Ni plasticity was observed from the earliest load levels. The superposition of tensile Poisson strain (in the transverse direction) on pre-existing tensile Ni strain due to TRS produces anisotropic yielding in binder regions. Yielding is progressive with applied strain, leading to a reversal of transverse binder strain, and anisotropic relaxation of the TRS. The effect is greatest for 20 wt.% Ni, where Ni constraint is much less than for 5 wt.% Ni. These results provide a quantitative basis for the mechanical origins of the toughness of cemented carbide composites. � 2005 Elsevier Ltd. All rights reserved.

In situ neutron diffraction measurements were performed on a tungsten carbide (WC)–10 wt.% cobalt (Co) cemented carbide composite subjected to compressive loading. The sample was subjected to consecutive load/unload cycles to −500, −1000, −2000 and −2100 MPa. Thermal residual stresses measured before loading reflected large hydrostatic tensile stresses in the binder phase and compressive stresses in the carbide phase. The carbide phase behaved elastically at all but the highest load levels, whereas plasticity was present in the binder phase from values of applied stress as low as −500 MPa. A finite element simulation utilizing an interpenetrating microstructure model showed remarkable agreement with the complex mean phase strain response during the loading cycles despite its under-prediction of thermal residual strains.

Thermal residual macrostresses and their gradients were studied in a series of polycrystalline diamond compacts (PDC) using neutron diffraction. The specimens comprised WC–Co cemented carbides with high temperature/high pressure (HTHP) sintered polycrystalline diamond (PCD) layers. Residual stresses were investigated in two as-sintered variants and after several post-sinter thermal treatments and bonding processes. Measurements were made of (1) the average in-plane stress in the diamond layer for each sample and (2) the average in-plane stress gradient in both the WC–Co substrate and the diamond layer in a subset of the samples. Average in-plane stresses in the diamond layer ranged from −250 to −582 MPa. Sintering process parameters, thermal treatments, and bonding were all found to affect residual stress levels and stress gradient characteristics. Measured average in-plane stress gradients are shown to differ substantially in some cases from linear elastic predictions.

The thermal residual macrostresses in a series of polycrystalline diamond compacts were studied using neutron diffraction. Measurements were made of (1) the average in-plane stress in the polycrystalline diamond table as a function of substrate-to-table thickness ratio; (2) the average in-plane residual stress gradient in both the WC–Co substrate and the diamond table; and, (3) the radial and hoop components of the residual stress in the diamond table as a function of radial position. The average in-plane stress in the diamond table increases in magnitude with increasing substrate-to-table thickness ratio, from −462 to −152 MPa as the ratio goes from 4 to 1. An in-plane residual stress gradient was measured that ranges from about −200 MPa at the free surface to +700 MPa at the substrate/diamond interface in the WC–Co substrate, and from about −600 MPa at the interface to −300 MPa at the free surface in the diamond. The hoop and radial stress components were measured at five points along a radius in the diamond table. The hoop stress was essentially constant (≈−470 MPa) and the radial stress ranged between about −150 and −350 MPa.