Effect of gradually decreasing laser power on the microstructure and properties of laser melting deposited Inconel 718Plus alloy thin-wall

Laser melting deposition (LMD) technology offers a novel method for fabricating superalloy thin-walled parts because of its significant advantage of rapidly producing near-net-shape moldings. However, the coarse columnar crystals in these deposited thin-walled parts resulted in poor mechanical properties, which significantly limited its wide application. To address this problem, a layer-by-layer decreasing laser power deposition strategy (LT) is proposed in this study, which can increase the cooling rate of the molten pool by reducing the thermal cycling. Results indicate that the thin walls of Inconel 718Plus alloy deposited by the LT strategy exhibit dendrites at heights of 4.5 mm (bottom region), 16.5 mm (middle region) and 28.5 mm (top region). The Laves phase at the bottom of the LT alloy thin-wall was randomly distributed granular, which gradually transformed into granular, short-chain and its mixed structures with increasing height. Formation of long-chain Laves phases was hindered by the connection of dendrites. The densely distributed granular Laves phase in the LT strategy alloy thin wall could effectively transfer and dispersed the stress and hindered the crack initiation and extended. Compared to the bottom region, the yield strength of the LT alloy thin-wall in the middle and top region increased by 6.7 % and 12.6 %, and the tensile strength increased by 10.7 % and 16.2 %. In conclusion, the alloy thin-walls fabricated by the LT strategy exhibit superior strength and more balanced mechanical properties.