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Binary alloys; Cobalt alloys; Cobalt metallography; Density functional theory; Molybdenum alloys; Molybdenum metallography; Shear flow; Strain hardening; Ternary alloys; Titanium metallography, Dislocation sources; Electron channeling contrasts; Elevated temperature; Higher-energy barriers; Mechanical behavior; Planar fault energies; Slip band formation; Strain hardening behavior, Titanium alloys
Abstract:
We investigated the flow behavior of γ/γʹ-strengthened Co-12Ti and Co-12Ti-4Mo (at.) alloys at room and elevated temperatures (up to 900°C) by electron microscopy and density functional theory. The Mo-added 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 ~25 larger γʹ volume fraction and ~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 γʹ precipitates. These effects are due to a reduced γ channel width and substantial hardening effect of γʹ-Co3(Ti,Mo) in the ternary alloy as well as due to the large shear modulus difference between γʹ and γ. © 2020
