Evolution of Laves phase related to tensile properties in cast ATI 718Plus under pulsed electric current

Abstract

The Laves phase will seriously deteriorate the subsequent hot working and welding performance of cast ATI 718Plus. In traditional homogenization annealing, two-stage treatment is used to prevent the formation of harmful eutectic structures due to the initial melting of the low-melting point Laves phase. This has several obvious disadvantages including high processing temperature, long processing time and complicated operation. Electrical pulsed treatment, as a new efficient, feasible and energy-saving green means, has rapidly achieved the dissolution of Laves phase. The increase in diffusion rate of Nb element in Ni matrix by pulsed electric current is due to the enhancement of defect migration and vacancy defect density, leading to a significant enhancement in the diffusion kinetics and accelerating the dissolution of Laves phase. Laves phase dissolution process under the pulsed electric current is from the aggregated state accompanied by dense needle like η phase to the discrete state accompanied by sparse needle like η phase, finally forming a single long strip and being dissolved into an intermittent state until it disappears. In all, using pulsed electric current instead of traditional heat treatment for annealing cast ingots has the potential to achieve one-step homogenization, completely dissolving the Laves phase while eliminating element segregation.