A new approach to improve strength and ductility of laser powder deposited Inconel 718 thin-wall structure

Laser powder deposition of Inconel 718 superalloy has been considered as a promising technique for the restoration of damaged aerospace components. A novel gradient laser power (GLP) deposition method is proposed to build Inconel 718 thin-wall structures by gradually reducing laser powers. The method not only alleviates micro-segregation but also tunes detrimental Laves phases’ content, size and morphology by controlling the solidification conditions. Macroscopic features, geometrical characteristics (layer widths and layer heights), porosity, tailored microstructure, microhardness and room temperature tensile properties are systematically investigated. A unique microstructure containing discrete fine Laves phases and a mixture of equiaxed grains and fine columnar grains with no obvious texture is obtained in GLP samples due to the enhanced cooling process and multidirectional heat flux. The relationships among processing parameter, microstructure and mechanical properties are discussed in detail. Compared with samples deposited by the conventional constant laser power (CLP) deposition method, GLP samples exhibit an excellent combination of strength and ductility with considerable yield strength, high ultimate strength, prominent strain hardening exponent and superior ductility of 40%. The GLP method provides a useful strategy to tailor microstructures and improve mechanical properties by purposely manipulating processing parameters.