Effect of heat treatment on microstructure and mechanical properties of the hot-isostatic-pressed Inconel 718 powder compact

• Develop a new heat treat method for the HIPed powder metallurgy Inconel 718.
• Find the reason for the low ductility of the solution and aged alloy.
• Explain the reason for the low yield strength of the direct aged alloy.

The present study deals with the optimization of the mechanical properties of the hot-isostatic-pressed Inconel 718 powder compact. Several heat treatments, including the solution plus aging with different solution temperature and the direct aging scheme, have been designed based on the phase relations of Inconel 718 and been employed for the optimization. The results indicate that the direct aging heat treatment is the best one, because it ensures a good balance of the strength and ductility of the powder compact. The tensile and stress rupture properties of the direct aged alloy have all met the specifications for Inconel 718. Solution process leads to a decrease of grain boundary strength and poor ductility because of the precipitation of carbide and δ phase at the prior particle boundaries or formation of thermal induced porosities at the triple junctions, and is then not appropriate for the powder compact. Yield strength of the direct aged alloy is a little lower than the solution treated alloy because of over aging of the γ′′ precipitates.