摘要
The study presents an innovative methodology that integrates two-stage heat treatments for pack cementation and aging hardening aimed at improving the high-temperature performance of Al0.2Co1.5CrFeNi1.5Ti0.3Nb0.05 high-entropy superalloys within single heating process. Initially, the two-stage heat treatment effectively suppressed discontinuous precipitates (DP) and optimized the distribution of the γ′ phase, leading to enhanced mechanical strength and ductility at the elevated temperature of 600 °C and 700 °C. Additionally, the pack cementation process further improved oxidation resistance by generating a dense aluminized coating, which exhibited commendable thermal stability at 1100 °C. High-temperature tensile tests conducted at 600 and 700 °C increased in yield strength and ultimate tensile strength by 7%, while maintaining almost equivalent levels of elongation and ductility. In cyclic oxidation tests at 1100 °C, the two-stage aluminized alloys showed minimal weight loss and a stable coating structure. In comparison to the Al0.2Co1.5CrFeNi1.5Ti0.3Nb0.05 alloys without coatings, this approach significantly improved isothermal oxidation resistance over a duration of 200 h and demonstrated superior thermal cyclic oxidation resistance after 90 cycles at 1100 °C. The coatings resulting from the two-stage heat treatment facilitated a microstructural transformation from Ni2Al3 to NiAl while the dense α-Al2O3 layer provided protection to the substrate during oxidation.
•Single-process heat treatment combines aging and surface coating.•Two-stage aluminization enhances HESA strength and oxidation resistance.•γ′ precipitate control suppresses DP and improves high-temperature ductility.•Aluminide coating forms stable α- Al2O3, enhancing 1100 °C oxidation durability.