Effect of single aging treatment on tensile and stress rupture property of MAR-M246 superalloy

Taking investment-cast MAR-M246 superalloy as the research material, a single aging treatment is adopted to replace the conventional solution plus double aging heat treatment, and the effects of single aging treatment on the microstructure, room-temperature/high-temperature tensile properties, and medium/high-temperature stress rupture properties of MAR-M246 superalloy are investigated. A high-resolution field-emission scanning electron microscope (FE-SEM) is used to characterize the microstructures and fracture morphologies of the as-cast and aged alloys, while tensile and stress rupture tests were carried out on alloys under different states. The results show that the microstructures of both as-cast and aged MAR-M246 superalloys consist of γ matrix, γ′ precipitates, blocky intragranular MC carbides, strip-like intergranular MC carbides, and γ+γ′ eutectic phases. After aging treatment, the volume fraction of γ′ precipitates increases from 42.68% in the as-cast alloy to 49.85% in the aged alloy, and the average size of γ′ precipitates rises from (301±9) nm to (321±12) nm with a more uniform size distribution; meanwhile, the cubicity of γ′ precipitates is markedly enhanced after aging. After aging, the room-temperature yield strength of MAR-M246 superalloy is slightly improved, and the elongation after fracture at 900 ℃ increases significantly. Under the condition of 760 ℃ and 724 MPa, the stress rupture life of MAR-M246 superalloy is remarkably extended from 18.15 h (as-cast) to 38.23 h (aged), and the stress rupture elongation rises from 3.14% (as-cast) to 5.4% (aged). However, at 980 ℃ and 225 MPa, the stress rupture life declines from 79.58 h (as-cast) to 45.48 h (aged). These phenomena are mainly attributed to the fact that the γ′ precipitates with higher cubicity generated during aging are prone to rapid coarsening and rafting.