Effects of Mo on the mechanical behavior of gamma/gamma'-strengthened Co-Ti-based alloys

Abstract

We investigated the flow behavior of gamma/gamma'-strengthened Co-12Ti and Co-12Ti-4Mo (at.%) alloys at room and elevated temperatures (up to 900 degrees C) by electron microscopy and density functional theory. The Moadded alloy exhibited an enhanced compressive yield strength and strain hardening behavior as compared to the reference binary alloy. This behavior could be attributed to a similar to 25% larger gamma' volume fraction and similar to 7% higher planar fault energies in Co-12Ti-4Mo. Using electron channeling contrast imaging, we observed interrupted slip bands in the Co-12Ti-4Mo alloy deformed to a strain of 6%, which led to enhanced strain hardening, in contrast to extended slip bands along {111} planes in the Co-12Ti alloy. Interrupted slip band formation in Co-12Ti-4Mo could be explained by rapid exhaustion of dislocation sources and a higher energy barrier required to cut the gamma' precipitates. These effects are due to a reduced gamma channel width and substantial hardening effect of gamma'-Co-3(Ti,Mo) in the ternary alloy as well as due to the large shear modulus difference between gamma' and gamma.