Effect of Delta Phase on the Hot Deformation Behaviour and Microstructural Evolution of Inconel 718

Abstract

In order to investigate the influence of -phase precipitation during high temperature forging of Inconel 718, hot axi-symmetric compression tests have been performed on specimens with two distinct initial microstructures: i) as-received material containing a dense population of  precipates at grain boundaries and along intragranular slip planes, and ii) material solution-treated to dissolve the  phase. Results indicate that the presence of  leads to a slight increase in peak stress and a proportionately greater post-peak reduction in flow stress, as compared to solution-treated material. For both types of microstructure flow softening is associated with grain refinement, but in different ways: in -free material conventional dynamic recrystallisation leads to the formation of new grains, whereas the presence of plate-like  appears to cause the mechanical break-up and segmentation of prior grains.