Effect of heat treatment on microstructure and mechanical properties of laser solid forming Inconel 718 superalloy

The effects of heat treatment on the microstructure and mechanical properties of laser solid forming Inconel 718 superalloy have been investigated. As compared with as-deposited samples, direct aged (DA) microstructure of laser solid formed (LSF) Inconel 718 changed little, and still presents the microstructural characteristic of columnar dendrites which grow epitaxially from the substrate. However, the hardness and tensile strength of DA samples increase obviously. Three technology of homogenization, solution and double aging heat-treatment (960STA) result in complete dissolution of interdendritic Laves phase and the reduction of Nb segregation. Further the solution treatment results in the precipitation of acicular δ phase along grain boundaries, and the tensile strength and plasticity both reach the wrought standard of Q/3B 548-1996 at room and high temperature. The tensile fracture surface of DA samples presents anisotropic feature of dimples along deposition orientation of columnar dendrites array, which is similar to that of the as-deposited samples. It is found that the distribution anisotropy of dimples in LSF samples disappeared through 960STA treatment.