AN INVESTIGATION ON THE STRENGTHENING OF INCONEL 718 SUPERALLOY BY THERMAL MECHANICAL TREATMENTS

Abstract

The Ni-Fe base disk superalloy Inconel 718 under normal heat treatment and thermal mechanical treatment conditions has been studied in this investigation. It was found that the segregation of alloying elements and the detrimental effect of δ-Ni3Nb phase could be reduced notably after the present thermal mechanical treatments. The experimental results indicated that the tensile strength and fatigue properties as well as the ductility of the alloy were increased substantially with its stress rupture lives comparable to that under normal heat treatment condition. The improvement in these mechanical properties of the alloy after thermal mechanical treatment can be ascribed to the refinement of microstructures and the strengthening of grain boundary regions by dispersed granular δ-Ni3Nb particals, which, in turn, alternate the fracture process of the alloy at elevated temperature, i.e. a change from an intergranular cleavage rupture to a ductile “dimple” fracture.