X-ray diffraction was used to determine the thermal residual stresses that develop in a functionally graded WC-Co composite. The gradient was continuous within a distance of about 40 μm below the surface and consisted of varying WC and Co phase volume fractions. Thermal residual stresses develop due to the thermal mismatch between the WC and the Co phase during cooling from the liquid-phase sintering temperature (1450°C). Pole figures were obtained in order to determine optimal sample orientations that provided adequate intensity for measurements in the Co phase. Stresses were measured in both WC and Co phases at various depths. For WC, the in-plane compressive residual stresses varied approximately between -300 MPa to -500 MPa with distance below the surface. For the low volume fraction Co phase, the mostly hydrostatic tensile residual stresses were approximately 1 GPa. The changes in the magnitude of the residual stresses can be related to the changes in the Co phase content through the graded zone. Microstresses in the graded zone are attributed to the thermal mismatch between the Co phase and WC. The compressive macrostresses were determined to be affected by the compositional gradient and hence varying the Co content in the gradient is expected to affect these stresses.
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