Study on microstructure and mechanical properties of laser rapid forming Inconel 718

Inconel™ 718 (IN718) has been deposited using laser rapid forming (LRF) from the gas atomized (GA) and plasma rotation electrode preparation (PREP) powders. The mechanical properties of LRF IN718 were evaluated and compared in between as-deposited and heat-treated state. The results show that the existence of the porosities in as-deposited samples, caused by the hollow particles in the GA powders, results in the low ductility and stress rupture properties for LRF GA IN718, since it will promote the occurrence of the micro-porous coalescence failure in the tensile samples. However, the ultimate tensile strength for heat-treated LRF GA IN718 is comparable to that of the wrought IN718, which is 1.5 times of that of the as-deposited samples. It is found that there exists a continuous thin film of Nb-rich MC carbides along the grain boundaries on the fracture surface of the stress rupture samples, which makes cracks initiate and propagate along this path easily, which also results in the poor stress rupture life for LRF GA IN718. The porosities and microcracks in LRF sample were successfully eliminated by using PREP powders, which leads to a substantial improvement in both tensile and stress rupture properties of LRF IN718.