Effect of heat treatment on carbides, microstructure uniformity and creep property of DZ125 nickel-based alloy

Abstract The effect of solution temperature on the carbide evolution and creep properties of DZ125 directional solidification nickel-based alloy is investigated through solution treatment at different temperatures, mechanical property tests, and microstructure observation. The investigations show that after the low-temperature solution treatment, the dendrite/inter-dendrite regions have obvious microstructure inhomogeneity. The γ′ phase in inter-dendrite regions is coarse, while that in dendrite regions is relatively fine, and some of the massive MC-type carbides in the as-cast alloy are transformed into sieve mesh. After the high-temperature solution treatment, the coarse γ′ phase in inter-dendrite regions is eliminated, and the massive MC-type carbides are transformed into granular M 23 C 6 -type carbides to be dispersively distributed at grain boundaries and intragranular regions. The creep properties of alloys being treated in high-temperature solution are substantially improved at temperatures around 800 °C compared to those of the low-temperature solution-treated alloys. At the late creep stage, under low-temperature solid solution treatment, cracks in the alloy preferentially initiate near massive carbides at grain boundaries. Under high-temperature solid solution treatment, cracks in the alloy preferentially initiate at grain boundaries and the granular carbides act as pegs to the cracks, which hinder crack extension.