Improvement of microstructure and mechanical properties of Inconel718 by the synergistic strategy of laser power and interlayer temperature control in laser directed energy deposition

Abstract

This paper addresses common issues such as microstructure defects, columnar grains, and elemental segregation in Laser Directed Energy Deposition (LDED) of Inconel718 superalloy thin-walled components. A novel synergistic control strategy for the LDED process is proposed. This strategy involves decreasing the input laser power layer by layer and forcibly lowering the interlayer temperature with forced air cooling, aiming to improve the microstructure and mechanical properties of Inconel718 superalloy thin-walled components. The research results show that compared with the traditional LDED process, the LDED process using the novel synergistic control strategy enhances the stability of the molten pool in each deposition layer, maintains the constant width of each deposition layer, significantly reduces porosity, and improves the material density of the components. Under the synergistic strategy, discrete fine Laves phases, as well as a mixed structure of disorderly grown fine columnar grains and equiaxed grains, were formed in the Inconel718 thin-walled components. These improvements in microstructure have led to an increase in the microhardness, tensile strength, yield strength, and elongation of the components by 9.30%, 41.12%, 26.05%, and 40%, respectively. Further analysis of the porosity, grain morphology, and distribution of Laves phases in the components reveals the strengthening mechanism of the new synergistic strategy proposed in this paper. The reasons for the improvement in tensile properties include HAGB (High Angle Grain Boundary) strengthening, LABG (Low Angle Grain Boundary) strengthening, dislocation strengthening, pore healing, the formation of discrete fine Laves phases, and the reduction of polarization density. This study provides an effective technical approach for the LDED of high-performance Inconel718 superalloy thin-walled components.