Abstract: Nickel-based superalloy TS5 was prepared by using selective laser melting (SLM) technology, and the effect of heat treatment with various heating temperatures, rates and holding time on the microstructure and mechanical properties of the alloy was analyzed. The results show that the proportion of cracks in the as-deposited TS5 alloy is 0.07%, with the cross-sectional average grain diameter of 66.94 μm. The TS5 alloy has a low cracking tendency of printing forming and a stable formed microstructure. When the as-deposited TS5 alloy is heated up to 900 ℃ with 0.1 ℃/s, γ′ phase precipitates in the heating process, while the faster heating rate can inhibit the precipitation of γ′ phase during the heating process, especially when the heating rate is greater than 50 ℃/s, the precipitation of γ′ phase is completely inhibited. When holding at 850 ℃ for 10, 60 and 240 min respectively, the size of γ′ phase is 22.2, 40.5 and 58.9 nm respectively, the volume fraction of γ′ phase is 26.2%, 37.7% and 47.1% respectively, meaning that the amount of precipitation gradually increases. The tensile test shows that the tensile strength of the as-deposited TS5 alloy gradually decreases with increase of the heat treatment temperature. The yield strength at 650 ℃ and 750 ℃ is 873 MPa and 768 MPa respectively, while the brittle fracture occurs during the tensile process at 850 ℃ and 950 ℃. The electron back-scatter diffraction results show that the cracks mainly occur in the high angle grain boundaries. In summary, a reasonable rapid heating combined with a short isothermal holding time is beneficial for avoiding phase transformation internal stress during the heating process. Moreover, effectively improving grain boundary strength is crucial for the TS5 alloy formed by SLM to resist the deformation and cracking during heat treatment process.

Key words: nickel-based superalloy, selective laser melting, heat treatment, microstructure, properties, crack