Microstructure development and superplasticity in Inconel 718 sheet

Abstract

Within the range of temperatures and strain rates investigated, mechanical testing identified the optimum forming condition for Inconel 718 sheet as being 965°C with a strain rate of 10^-4 s^-1. A detailed investigation of the microstructural behaviour under these deformation conditions was carried out and is reported here. Typically superplastic deformation would generate an enhanced rate of grain growth. This was not the case with the present material; instead it was found that a slight apparent grain size reduction occurred and there was evidence of substantial dislocation activity. It was concluded that the material was deforming on the borderline between 'true' superplasticity and normal slip based deformation.