X-RAY STRESS ANALYSIS OF WC-CO CERMETS .I. PROCEDURES

The factors that influence the measurement of stress by the “two‐exposure” X‐ray diffractometer technique in the WC phase of WC‐Co cermets were studied. Chromium Karadiation was used on the (1012) line of WC (2θ= 135.8°). The X‐ray values of Young's modulus and Poisson's ratio are 105×106 psi and 0.19, respectively, and the X‐ray stress factor is 1.51 × 108 psi/Å. The measured stresses are biaxial. Because penetration is limited to less than 5 μm for CrKa radiation, extreme care in surface preparation and heat treatment is required. A suitable preparation is metallographic polishing with 6 μm diamond followed by annealing in hydrogen at 750°C. This treatment allows measurement of about 40, 000 psi compressive temperature stress inherent in the WC particles resulting from differences in coefficients of thermal expansion between WC and Co. Mechanical stresses can also be measured; they arise from external forces such as grinding, polishing, and sand blasting. Mechanical and temperature stresses cannot always be clearly distinguished, however. Copyright © 1969, Wiley Blackwell. All rights reserved