|About this Abstract
||2017 TMS Annual Meeting & Exhibition
||Gamma (FCC)/Gamma-Prime (L12) Co-Based Superalloys II
||Mechanical Behavior of Polycrystalline (L12)gamma-prime-strengthened Co-base Superalloys
||Peter Bocchini, Daniel Sauza, James Coakley, Qinyuan Liu, David N Seidman, David C Dunand
|On-Site Speaker (Planned)
||David C Dunand
Conventional Ni-base and emerging Co-base superalloys are both characterized by large volume fractions of (L12) gamma-prime precipitates embedded in a (f.c.c.) gamma matrix. This unique microstructure confers excellent creep strength as well as the so-called flow-stress anomaly, by which the yield strength increases with temperature, exhibiting a maximum between 700-825 °C. However, polycrystalline Co-Al-W suffers from intergranular cracking, and the anomalous flow stress response of (L12) Co3(Al, W) is reduced compared to (L12) Ni3Al. We present an overview of our work improving these properties through alloying additions: B improves the creep strength of Co-Al-W when in sufficient amounts to promote W-borides, and the creep strength of ‘W-free’ Co-Ni-Al-Mo-Nb is comparable to ternary Co-Al-W with reduced density. Ti and Ni additions dramatically improve the anomalous flow stress response, and the creep strength of Co-5.6Al-5.8W-6.6Ti-0.12B at.% is comparable to Co-9Al-9W-0.12B at.% despite lower precipitate volume fraction and lack of borides along GB.