Effect of solution heat treatment on the microstructure and mechanical properties of Inconel 625 superalloy fabricated by laser solid forming

Highlights: • The microstructural evolution of solidification during the LSF process is explained. • The formation and dissolution of Laves phase are discussed in detail. • The effect of solution temperature on mechanical properties is investigated. • The contribution of different strengthening mechanisms is discussed in detail. In this study, the effect of solution heat treatments on the microstructure and mechanical properties of Inconel 625 superalloy fabricated by laser solid forming was investigated. The microstructure of deposit was mainly composed of columnar grains, which didn't change until the solution temperature reached 1200 °C after solution heat treatment. Due to the large size Laves phase which can pin grain boundary and obstruct grain boundary migration, the recrystallization fully occurred when the solution temperature exceeded 1200 °C. With the increment of the solution temperature, the average diffusion coefficient of solute elements and the dissolution velocity increased obviously. Besides, the volume fraction and size of Laves phase decreased, and the dislocation density decreased apparently. As a result, the microhardness and yield strength decreased with the increment of the solution temperature, but the tensile strength didn't change much after solution heat treatment, and the elongation increased significantly with the solution temperature improving. The room-temperature tensile properties in different states of Inconel 625 fabricated by laser solid forming were higher than those of Inconel 625 fabricated by casting.