Plastic deformation of polycrystals of Co₃(Al,W) with the L1₂ structure

The plastic behaviour of Co₃(Al,W) polycrystals with the L1 ₂ structure has been investigated in compression from 77 to 1273 K. The yield stress exhibits a rapid decrease at low temperatures (up to room temperature) followed by a plateau (up to 950 K), then it increases anomalously with temperature in a narrow temperature range between 950 and 1100 K, followed again by a rapid decrease at high temperatures. Slip is observed to occur exclusively on {111} planes at all temperatures investigated. The rapid decrease in yield stress observed at low temperatures is ascribed to a thermal component of solid-solution hardening that occurs during the motion of APB-coupled dislocations whose core adopts a planar, glissile structure. The anomalous increase in yield stress is consistent with the thermally activated cross-slip of APB-coupled dislocations from (111) to (010), as for many other L1 ₂ compounds. Similarities and differences in the deformation behaviour and operating mechanisms among Co₃(Al,W) and other L1 ₂ compounds, such as Ni₃Al and Co₃Ti, are discussed.