High-temperature strength and deformation of γ/γ‧ two-phase Co-Al-W-base alloys

The high-temperature strength and deformation behavior of γ/γ‧ two-phase Co-Al-W-base alloys have been studied with polycrystalline and single-crystal materials. The ternary, quaternary and higher-order alloys containing Ta, Cr and/or Re exhibit flow stress anomalies above 873 K due to slip of pairs of 1/2〈1 1 0〉 superpartial dislocations on {0 0 1} planes, in addition to {1 1 1} planes, in the γ‧ precipitates. Compression tests on the single-crystal specimens reveal a true anomalous peak temperature of 1073 K for both ternary and Ta-containing quaternary alloys. Above the peak, the ternary alloy exhibits a rapid decrease in strength with temperature, as 1/2〈1 1 0〉 dislocations bypass the γ‧ precipitates without significant shearing. Conversely, the Ta-containing quaternary alloy sustains strength to higher temperatures due to the activation of 1/3〈1 1 2〉 partial dislocation slip that introduces a high density of stacking faults in the γ‧ precipitates.