Effects of Al on microstructural stability and related stress-rupture properties of a third-generation single crystal superalloy

Abstract

To examine the influences of minor modification of Al content on the microstructural stabilities and stress rupture properties, two alloys with minor difference in Al content were exposed isothermally at 1100 °C for 100 h, 500 h, and 1000 h, respectively. The microstructures were characterized before and after thermal exposure. It was found that when Al content was decreased by 0.4 wt %, the volume fraction γ′ decreased by 4 %, the size of γ′ increased by 40 nm, the matrix channel width increased by 5 nm, and the misfit degree of γ/γ′ phases increased by 0.006 % after heat treatment (HT). During thermal exposure, the alloy with low Al content had a better resistance to coarsening of γ′ phase and precipitation of μ phase. The γ′ particles of the alloy with high Al content tended to connect each other and coarsened along <100>directions; however, the γ′ particles of the alloy with low Al content remained cubic after 500 h. A serious coarsening behavior took place in the two alloys after aging for 1000 h. The structural stabilities were significantly improved. However, the change of 0.4 wt % Al content was found to have little effect on the high temperature stress-rupture properties.