Microstructure and mechanical behaviour of an advanced powder metallurgy nickel base superalloy processed through hot isostatic pressing route for aerospace applications

Abstract

An advanced powder metallurgy (P/M) nickel-base superalloy envisaged for aerospace applications is realized through hot isostatic pressing (HIPing) of inert gas atomized powder. Extensive characterization of the microstructural features at different scales by employing optical microscopy, SEM-EBSD and transmission electron microscopy (TEM) divulged multi-modal distribution of γʹ precipitates within austenitic γ-FCC matrix phase in the as-HIPed condition. Investigation of prior particle boundary precipitates (PPBs) through TEM and Electron Probe Micro Analysis (EPMA) techniques revealed the dominance of metallic oxides and MC type carbides. The suitability of the advanced P/M superalloy for realizing near-net shape components by Direct-HIPing for short duration aeroengine rotating components is assessed by evaluating the room temperature and elevated temperature tensile behaviour as well as stress-rupture life in the service temperature regimes. The yield strength and the ultimate tensile strength of the present alloy at 650 °C are found to be 850 MPa and 1275 MPa respectively combined with 28% of ductility which is comparable to those of the similar class of superalloys in service. On the other hand, the as-HIPed superalloy exhibited minimum 1000 h of stress rupture life around service temperatures and bettered the stress rupture life of wrought superalloy IN718 alloy showing its potential for fabrication of near-net shape components for aerospace applications.