Effect of δ Aging Treatment on Microstructure and Tensile Properties of Repaired Inconel 718 Alloy Using Laser Additive Manufacturing

Inconel 718 alloys with premade grooves arc repaired layer by layer with Inconel 718 spherical powder via the laser additive manufacturing process. The repaired Inconel 718 alloys arc then subjected to delta aging treatment at 800 degrees C. for different time (1, 8, 16, and 32 h) to study the effect of the aging time on the microstructure and tensile properties of the repaired layer. The results show that the Laves and strengthened gamma '' phases in the repaired layer gradually disappear with the increase of the aging time, whereas the 6 phase nucleates and grows on the basis of the stacking faults of the gamma '' phase on the close-packed plane through the shearing mechanism. In addition, needle-like precipitates appear in the delta phase of the repaired zone around the residual Laves phase and become larger with aging time. However, precipitates in the substrate metal preferentially nucleate and grow at the grain boundaries and eventually grow in parallel within the grains. Although the aging treatment can effectively improve the microhardness and tensile strength of the repaired zone and the substrate metal of Inconel 718 alloys, the hardness and mechanical properties decrease as the aging time continues to increase. After aging treatment for 1 h, the microhardnesses of the repaired zone and the substrate metal reach the highest values of 361 HV and 165 HV, respectively, and then gradually decrease with the aging time. Furthermore, with different aging treatments, all the tensile fractures of the repaired parts arc located in the repaired zone. The fracture surfaces arc flat, showing typical brittle fracture characteristics.