Effect of heat treatments on the microstructure and mechanical properties of René 104 superalloy manufactured by selective laser melting

In this work, the effect of direct aging (DA), solution at 1160 °C (S1160) and solution at 1160 °C + aging treatment (SA1160) on the defects, microstructure and mechanical properties of René 104 alloy fabricated by SLM was systematically investigated. The results demonstrated that the cracking density of DA samples increased by 85.1%, while that of S1160 and SA1160 samples increased by 30.2% and 35.4% respectively, and the porosity gradually increased with the increase of heat treatment temperature and time. After direct aging, the average grain size increased slightly to 61.1 μm, and a large number of striped γ' phases with the size of 36 nm were precipitated. After solid solution at 1160 °C for 1 h, recrystallization occurred, and some coarse columnar crystals were transformed into fine equiaxed crystals, the average grain size decreased to 47.5 μm, and the γ' phase had a bimodal distribution of 23 nm and 194 nm. During the subsequent two-stage aging treatment, all the coarse columnar crystals were transformed into equiaxed crystals with an average grain size of 56.2 μm, as well as the irregular γ' phase was transformed into a sub-sphere with an average size of 175 nm. A good deal of precipitated γ' phase is the main reason for the significant improvement of microhardness and tensile strength, while the increase of defect density reduces the elongation to some extent.