Mechanical properties of the ternary L1₂ compound Co ₃(Al, W) in singleand polycrystalline forms

The mechanical properties of Co₃(Al, W) with the L1₂ structure have been investigated both in single and polycrystalline forms. The values of all the three independent single-crystal elastic constants and polycrystalline elastic constants of Co₃(Al, W) experimentally determined by resonance ultrasound spectroscopy at liquid helium temperature are 15∼25% larger than those of Ni₃ (Al, Ta) butare considerably smaller than those previously calculated. When judged from the values of Poisson'sratio, Cauchy pressure and ratio of shear modulus to bulk modulus (G_h/B_h), the ductility of Co₃(Al, W)is expected to be sufficiently high. In the yield stress-temperature curve, a rapid decrease and an anomalous increase in yield stress is observed in the low and intermediate (1000-1100 K) temperature ranges, respectively. The former is concluded to be due to the solid-solution hardening effect whilethe latter is attributed to thermally activated cross-slip of APB-coupled a/2<110> superpartial dislocations from octahedral to cube slip planes.