Microstructure and tensile properties optimization of MIM418 superalloy by heat treatment

Solution plus ageing leads to the precipitation of finer and more homogeneous gamma' precipitates in comparison to direct ageing. Solution treatment at 1220 degrees C eliminates the large primary gamma' phase and replaces them with homogeneous secondary gamma' precipitates. Coarsening of gamma' 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 gamma' 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 degrees C x 24h aged specimens. (C) 2015 Elsevier B.V. All rights reserved.