Evolution of microstructure and mechanical properties as a consequence of tensile creep strain of NNS-HIPped nickel-based superalloy

Nickel superalloys are being widely used in high-temperature applications such as aerospace and power generation due to their excellent mechanical properties. However, long-term exposure to high temperatures under continuous stress leads to microstructural and mechanical degradation, making it unfit for service. Therefore, this study analyzes the creep behavior of astroloy fabricated via near-net shape hot isostatic pressing (NNS–HIP). NNS-HIP is a powder metallurgy technique enabling precise component fabrication that is difficult to manufacture through conventional methods by densifying loosened powders in a pre-designed capsule under high temperature and isostatic pressure with the help of compressed inert gas. Creep tests were conducted at different temperatures (650, 760 & 820 °C) and stress conditions. Optical and scanning electron microscopy (SEM) analysis revealed that increasing temperature influences the transition of grain boundary precipitates from discontinuous to interconnected morphologies, facilitating intergranular crack initiation and propagation. Additionally, hardness testing demonstrated a direct correlation between excessive precipitate coarsening and reduced mechanical properties, with a decline in hardness at 820 °C compared to 650 °C. The results emphasize optimizing operational temperature and stress parameters to mitigate detrimental precipitation and cracking, thereby improving the service reliability of HIPped Astroloy components.