Influence of Solid-Solution Treatment on the Microstructure and Mechanical Properties of a Ni-Cr Based Superalloy Fabricated by Selective Laser Melting

Abstract

A Ni-Cr based superalloy GH3230 was fabricated by selective laser melting and the effect of solid-solution treatment on the microstructure and mechanical properties was studied. The microstructure of the as-built specimen is composed of dendritic matrix, with coarse M₂₃C₆ carbides distributing along the grain boundaries and high-density dislocations in the dendritic arms. The solid-solution treatment at 1100 °C makes M₂₃C₆ carbides transform into M₆C carbides, but recrystallization in the matrix is limited. As the solid-solution temperature rises to 1230 °C, a large number of fine M₆C carbides precipitate, and a complete recrystallization structure form. At a higher solid-solution temperature of 1320 °C, the carbides are almost completely dissolved in the matrix phase and the proportion of low-angle grain boundaries is the lowest. The solid-solution treatment decreases the strength but increases the plasticity of the alloy. The solid-solution treatment of the printed GH3230 alloy at 1320 °C decreases the ultimate tensile strength from 940 to 618 MPa, but increase the tensile elongation from 18.6 to 48.5%. A good combination of strength and plasticity of GH3230 alloy could be achieved by solid-solution treatment.