The precipitation behavior effect of δ and γ" phases on mechanical properties of laser powder bed fusion Inconel 718 alloy

The mechanical properties of additively manufactured materials were mainly influenced by the precipitations in the microstructure. In this work, Inconel 718 (IN718) superalloy was fabricated by laser powder bed fusion (LPBF) and treated by solution and dual-aging treatments. The δ and γ" phases with different sizes and morphologies have been obtained by different solution temperatures. The precipitation behavior effect of δ and γ" phases on the room temperature tensile and high temperature stress rupture properties has been investigated. The results showed that the Laves phase formed in the as-fabricated sample. After solution heat treatment, the Laves phase dissolved and transformed to δ phase. As the solution temperature increased, the needle-like δ phase gradually dissolved, while only a little short rod-like δ phase remained. During aging heat treatment, the Nb element released from dissolved δ phase was beneficial to promote the precipitation of γ" phase. The content and size of nano-scale γ" phase significantly affected the yield strength of IN718 alloy. At higher solution temperature, the γ" phase with suitable size exhibited the highest yield strength of 1283 MPa. On the other hand, δ phase had a significant impact on high temperature stress rupture properties. The stress rupture life increased from 37.2 h to 52.5 h with decreasing volume fraction of δ phase.