Microstructure and Mechanical Properties of a Spray-Formed Superalloy

Abstract

The microstructural evolution and mechanical properties of a spray-formed superalloy were studied in this paper. Based on a better understanding of the microstructural evolution of the spray-formed superalloy during solution treatment, an optimum solution treatment process was obtained, namely, at 1,140 °C for 6 h, and air cooling (AC). The effects of the ageing treatments on the mechanical properties of the post-solution-treated spray-formed superalloy were evaluated using ageing harden curves and tensile testing. The results indicated that the maximum hardness value was achieved at 850 °C for 8 h, AC. Due to co-precipitation of primary and secondary γ′ precipitates during the heat treatment, the spray-formed superalloy obtained an excellent combination of yield strength (YS = 1,110 MPa), ultimate tensile strength (UTS = 1,503 MPa), ductility (elongation, EL = 21%) and excellent stress rupture properties at 650 °C (UTS = 1,209 MPa, EL = 15.8%). The heat treatment also improved the rupture life at 650 °C/950 MPa and 750 °C/539 MPa up to 140 h without rupturing. The tensile-fractured surfaces exhibit ductile transgranular failure feature. The optimum heat treatment process was determined to be 1,140 °C/6 h + 850 °C/8 h + AC.