Microstructure and tensile properties optimization of MIM418 superalloy by heat treatment

Solution plus ageing leads to the precipitation of finer and more homogeneous γ′ precipitates in comparison to direct ageing. Solution treatment at 1220 °C eliminates the large primary γ′ phase and replaces them with homogeneous secondary γ′ precipitates. Coarsening of γ′ particles according to Ostwald ripening mechanism is confirmed. An increase of the critical resolved shear stress (CRSS) is observed for the under-aged specimens, followed by a maximum of CRSS at γ′ particle size of around 100 nm and a decrease of CRSS for the over-aged specimen. This result agrees well with the highest yield strength and microhardness of the 750 °C × 24 h aged specimens.