The Influence of Heat Treatment on Microstructure Evolution and Mechanical Properties of Laser Selective Melting-Formed Nickel-Based Superalloys

This study employed selective laser melting (SLM) to fabricate GH4169 alloy, investigating its microstructural evolution and mechanical properties under two heat treatment conditions: solution treatment alone and solution treatment followed by aging. Tensile test results indicate that the yield strength and tensile strength of specimens in the solution-treated state increased by 16.8 and 2%, respectively. The yield strength and tensile strength of the solution-treated and aged specimens increased by 70 and 30.2%, respectively. The elongation of the solution-treated specimens decreased by 17%, while that of the solution-treated and aged specimens decreased by 29.2%. Using scanning electron microscopy, transmission electron microscopy, x-ray diffraction, and backscattered electron diffraction, observations were conducted on texture, microstructure, and grain morphology. Compared to the as-printed specimens, the solid solution-treated specimens exhibit increased γ′, γ′′ and δ phases, with overall grain size enlargement and an average grain size of 58.6 μm. Compared to specimens in the solution-treated state, specimens in the solution-treated + aged state exhibit smaller δ-phase dimensions, a further increase in the quantity of precipitated strengthening phases, and the emergence of numerous equiaxed grains exceeding 100 μm in size. The average grain size increased to 67.9 μm. After heat treatment, the Laves phases dissolve; δ phases precipitate during the solution treatment stage, and γ′ and γ′′ phases precipitate in the aging treatment stage. These phases play a key role in pinning dislocations and strengthening the matrix, which constitutes the primary reason for the improvement of the alloy’s mechanical properties.