X-RAY STRESS ANALYSIS OF WC-CO CERMETS .2. TEMPERATURE STRESSES

The effect of cobalt content on the temperature stress in WC‐Co cermets was measured using both the “one‐exposure” and “two‐exposure” X‐ray diffraction techniques. in the one‐exposure technique, strain is measured by comparing lattice spacings in the stressed, d8, and unstressed, d0, conditions. Nonresolution of the a1‐a2 doublet caused by adding Co to annealed WC shifts the apparent peak position to higher diffraction angles (smaller d8). Thus, the proper choice of d0 must be made so that in measuring both d0 and d8 similar diffraction peak profiles are used. These conditions have not always been considered, causing some previously reported results to be open to question. With the two‐exposure technique, no such difficulties exist, because similar peaks are compared at the two angular positions used for measuring d on the same sample. Because of shallow X‐ray penetration in WC, only biaxial temperature stresses at the surface are measured. These stresses are compressive, varying from ‐53, 000 psi for WC + 10 vol% Co to ‐24, 300 psi for 37 vol% Co. This trend is in disagreement with previous theories, which predict greater compressive stress as Co content increases. Copyright © 1969, Wiley Blackwell. All rights reserved