Effect of solution heat treatment on the microstructure and mechanical properties of laser melting deposited GH 5188 superalloy

GH 5188 is a solution strengthening cobalt-based superalloy, which is widely used for manufacturing hot components with service temperatures of 1000 ~ 1100 °C. GH 5188 superalloy was fabricated by laser melting deposition (LMD) followed by solution treatment. The effect of heat treatment temperature ranging from 1140 to 1260 ℃ on microstructure and tensile properties of as-LMD specimens was investigated. Optical microscope (OM) and scanning electron microscope (SEM) were used for microstructural observation, and transmission electron microscope (TEM) was employed for phase determination. The results showed that heat treatment did not affect phases within the as-LMD GH 5188 specimens, which were composed of γ, M 23 C 6 , M 6 C, and La 2 O 2 C 2 , whereas heat treatment temperature had an evident effect on the size and content of carbides. In general, heat treatment improved both the ultimate tensile strength (UTS) and the elongation (EL) of as-LMD specimens. With the increase of heat treatment temperature varying from 1140 to 1260 ℃, the UTS enhanced firstly to 1051.9 MPa and then decreased to 934.8 MPa. As the reason, Carbide dispersion distribution contributed to the increase of UTS below the heat treatment at 1180 ℃, and the decrease of volume fraction and size for carbide led to the decrease of UTS above the heat treatment at 1180 ℃. The EL increased slightly at first and then rose rapidly. On the contrary, YS monotonously decreased from 587.1 to 503.6 MPa. The dimples became deeper as the heat treatment temperature increased, indicating better toughness.