Effects of Mo on the mechanical behavior of γ/γʹ-strengthened Co-Ti-based alloys

• Published in: Acta materialia Vol. 197; pp. 69 - 80
• Main Authors: Im, Hye Ji, Lee, Subin, Choi, Won Seok, Makineni, Surendra Kumar, Raabe, Dierk, Ko, Won-Seok, Choi, Pyuck-Pa
• Format: Journal Article
• Language: English
• Published: Elsevier Ltd 15.09.2020
• Subjects: Cobalt-base superalloys; Deformation microstructure; Dislocation; Mechanical properties; Slip band; Cobalt-base superalloys; Mechanical properties; Slip band; Deformation microstructure; Dislocation
• ISSN: 1359-6454; 1873-2453
• DOI: 10.1016/j.actamat.2020.07.037

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. [Display omitted]