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

The high-temperature strength and deformation behavior of gamma/gamma ' 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 < 110 > superpartial dislocations on {001} planes, in addition to {111} planes, in the gamma' 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 < 110 > dislocations bypass the gamma' precipitates without significant shearing. Conversely, the Ta-containing quaternary alloy sustains strength to higher temperatures due to the activation of 1/3 < 112 > partial dislocation slip that introduces a high density of stacking faults in the gamma' precipitates. (C) 2007 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.