Improving surface quality and superficial microstructure of LDED Inconel 718 superalloy processed by hybrid laser polishing

Abstract

In the present research, a hybrid laser polishing technology combining pulsed laser and continuous wave laser was applied to polish the surface of laser directed energy deposition (LDED) Inconel 718 superalloy components. The surface morphology, microstructure evolution and microhardness of the as-fabricated, the single pulsed laser polishing (SPLP) and the hybrid laser polishing (HLP) processed samples were investigated. The results revealed that the as-fabricated sample has a rough surface with sintered powders. In the matrix, the NbC carbide and Cr2Nb based Laves phase array parallel to the build direction and the small γʺ-Ni3Nb particles precipitate in matrix uniformly. The surface roughness of the as-fabricated sample is 15.75 μm which is decreased to 6.14 μm and 0.23 μm by SPLP and HLP processing, respectively. The SPLP processing refines the grains and secondary phase significantly in the remelted layer which is reconstructured with the cellular structure and plenty of substructures. The HLP processing also refines the grain and secondary phase but the secondary phases still exhibit array distribution. In addition, the tangled dislocations pile up along the interface of secondary phases. Compared with the as-fabricated sample, the SPLP processing decreases the surface microhardness but the HLP processing increases the surface microhardness, and the Young's elasticity modulus of surface layer is improved by SPLP and HLP processing to 282 ± 5.21 GPa and 304 ± 5.57 GPa, respectively.