Effect of Post-HIP Heat Treatments on the Microstructural Evolution of High Temperature Ni-based Superalloy

Ni-base superalloys are commonly used in aircraft engines due to their exceptional combination of high temperature strength, toughness, great corrosion and oxidation resistance. Superalloys with high γ´ volume fraction, such as Astroloy, are desirable for high temperature applications, in combustors and turbines. However, these alloys are difficult to process by conventional cast and wrought, thus Near Net Shape Hot Isostatic Pressing (NNS-HIP) is the preferred manufacturing option. To increase the as-HIP properties, tedious post-heat treatments are currently applied. This work analysed the microstructural evolution after several heat treatment and relates it with the mechanical properties. Heat-treatments were designed to simplify post-processing with no significant impact in mechanical properties. The microstructural analyses were performed by FEG-SEM and ImageJ to quantify the microstructural features (specifically, γ´). Tertiary γ´ have been proved to be the main strengthening face, and its size and volume fraction are directly related with material’s properties.