Mechanism of intermediate temperature abnormal plasticity in Co–Al–W-base superalloy

Abstract

The mechanism of intermediate temperature abnormal plasticity of Co–Al–W-base superalloy was investigated. The interrupted tensile specimens were systematically characterized through high-temperature XRD, SEM, as well as TEM. The superalloy exhibits a low elongation (approximately 5.2 %) at 700 °C for two reasons. On the one hand, the γ/γ′ lattice mismatch decreases with the increasing temperature (0.36 % at 600 °C, 0.25 % at 700 °C, and 0.19 % at 800 °C). The low γ/γ′ lattice mismatch facilitates a/2<110> type dislocation to cut into the γ′ phase in the form of paired a/2<110> type dislocation. When the paired a/2<110> type dislocation slips out from the γ′ phase and it will be hindered by MC carbide, increasing the stress concentration around MC carbide, so that it leads to early MC carbide breaking and microvoid forming. On the other hand, the stacking fault energy decreases with the increasing temperature. The a/2<110> type dislocation easily resolves into two a/6<112> type partial dislocations in the γ′ phase at 800 °C. The a/6<112> type partial dislocation suppresses the surrounding a/2<110> type dislocations to cut into the γ′ phase, relaxing the stress concentration around MC carbide. Therefore, the abnormal plasticity of Co–Al–W-base superalloy occurs at 700 °C.