Investigation of microstructure and mechanical properties on surface-modified inconel 718 Alloy

Abstract

This study was carried out to evaluate the development of the microstructure and mechanical properties of a surface-modified post-heattreated Inconel 718 alloy. The friction stir process (FSP), as the surface-modification method, was applied to an overlap-welded Inconel 718 alloy. The FSP was conducted at a tool rotation speed of 200 rpm and a tool downforce of 39.2 kN; post-heat treatment was carried out in two steps: (i) at 720°C for 8 h and (ii) 620°C for 6 h in vacuum. FSP was effective for developing grain refinement, accompanied by dynamic recrystallization, thus improving the mechanical properties compared to the original overlap-welded material. Furthermore, the post-heat treatment after FSP accelerated the formation of precipitates such as gamma prime (€A) and metalcarbon (MC) carbides, which led to a significant improvement in mechanical properties. In this study, the development of the microstructure and the improvement of the mechanical properties through the application of FSP and post-heat treatment are systematically discussed. ©2013 The Japan Society for Technology of Plasticity.