Effect of solution cooling rate on microstructure evolution and mechanical properties of Ni-based superalloy ATI 718Plus

Abstract The effects of solution cooling rate on microstructure, mechanical properties and the corresponding deformation mechanisms of ATI 718Plus superalloy were investigated. With solution cooling rate decreasing, the volume fraction and the size of primary γ´ phase both increase, which is attributed to that the lower solution cooling rate is beneficial to the migration and interaction of alloy elements in γ´ phase. The tensile strength and microhardness of sample were improved by decrease of solution cooling rate, which is mainly attributed to increase of volume fraction of primary γ´ phase. Specially, the elongation of sample with the lowest solution cooling rate (furnace cooling) was also higher than other samples probably due to large size of primary γ´ phase, which is beneficial to plastic deformation by helping promote active movement of dislocations. In general, three samples exhibit the mixed deformation mechanisms characterized by shearing and bypassing, but primary deformation mechanism of three samples was different, which depends on different precipitation behavior of γ´ phase resulting from different solution cooling rate. The sample that was furnace cooled from solution temperature exhibits a typical shearing deformation mechanism, including stacking faults (SFs) and dislocations shearing, while other two samples with the higher solution cooling rate primarily show an Orowan looping deformation mechanism. The result of calculating critical resolved shear stress (CRSS) exhibits an increasing tendency of SFs shearing while decreasing tendency of Orowan looping with solution cooling rate decreasing, which is corresponding to experimental results.