Influence of processing parameters on the thermal history, microstructure and tensile properties of Inconel 738 produced by laser directed energy deposition

Abstract

In this paper, laser directed energy deposition (LDED) technology was applied to produce non-weldable Inconel 738 parts. The influence of processing parameters including laser power, scanning speed and powder feeding rate on the thermal history of molten pool and the morphology of single track was evaluated. Considering the surface quality and deposition efficiency, the appropriate processing parameters for multilayer deposition were selected. Then the impact of laser power on the microstructure evolution and tensile properties of IN738 thin-wall parts was investigated. The research results show that increasing the laser power could increase the peak temperature and molten pool lifetime, but decrease the cooling rate. Increasing the scanning speed significantly increased the cooling rate but had little effect on the peak temperature. The thermal history was hardly affected by the powder feeding rate, but a too high powder feeding rate caused the particle adhesion and decline of surface quality. The microstructure of LDED-manufactured IN738 was composed of dense and fine dendrites. The higher laser powers of 800 W and 1000 W created higher temperature gradient within the molten pool, which promoted the epitaxial growth of dendrites. However, the long dendrites were prone to be torn apart under the transverse tensile stress, which was detrimental to the elongation and ductility. By comparison, when the laser power was 600 W, the growth direction of dendrites between adjacent layers was different and exhibited the best ductility.