Microstructure and Mechanical Properties of Crack - Free Ni - Based Gh3536 Superalloy Fabricated by Laser Solid Forming

In this work, LSF was used to fabricate specimens from nickel-based superalloy GH3536 on the forged GH3536 alloy substrate. Tensile and fatigue crack growth (FCG) testing was carried out in both H and V specimens with the condition at 25℃ and 500℃. Three regions can be detected in the specimen: the additive manufacturing zone (AM), the heat affected zone (HAZ) and the substrate. M 23 C 6 and M 6 C carbides were found in the specimens due to the segregation of elements during thermal cycling, only a small amount of hole defects were observed in the specimens, and no cracks were found. Due to the presence of many fine dendritic substructures in the AM, which acts as fine grain reinforcements, the hardness of AM is 7 % higher than that of the substrate at room temperature, and it shows much higher ultimate tensile strength than that of forged GH3536 alloy. The tensile test results show that the specimens have obvious anisotropy, and the H specimens displayed higher strength (up to 855.3 MPa ultimate tensile strength at 25℃). It is worth noting that there is no obvious anisotropy in the FCG rates of the specimens in different directions, and only when the ΔK is about 45–60 MPa m1/2, the FCG rates of the vertical specimens are higher. The increase in temperature will significantly reduce the tensile properties of the specimens and increase the FCG rate. Serrated tensile flow was observed on the stress–strain curve at temperatures of 500℃, which is related to the migration of solute atoms (Mo and Cr) in the nickel matrix and the obstruction of dislocation movement by grain boundaries