Stress Relaxation Properties and Microscopic Deformation Structure in Bending of the C7025 and C7035 Alloy

Abstract

Stress relaxation tests in cantilever bending were performed on the C7025 and C7035 alloys at 298 K and 393 K, respectively. The effect of stress-relief treatments on stress relaxation properties was investigated. The structural changes associated with the stress relaxation process were examined using transmission electron microscopy. The stress relaxation curve fits well to empirical formula σ* = [K’ln(t + α0) + C]−n for stress relaxation. The curves can be split into two stages. The stress drops fast at first and then it gets slower in the second stage, and tends towards a certain limited value after a long time. The curve and microstructure reveal that the C7035 alloy has a lower rate of stress relaxation and a higher anti-stress relaxation capacity than the C7025. The first reason is that the movement of vacancies required by spinodal decomposition is inhibited, and the quantity of cobalt-containing vacancies decreases dramatically in the C7035 alloy. The other reason is that the precipitated phases became uniformly diffused in the C7035 alloy. The precipitate phase is uniformly distributed in the grain boundaries and the matrix, during the relaxed condition, and thus the dislocation movement is blocked by the precipitate.