A functionally graded material design from stainless steel to Ni-based superalloy by laser metal deposition coupled with thermodynamic prediction

Abstract

Extreme performance requirements are demanding materials with functional microstructure and properties. Additive manufacturing (AM) is an efficient method to fabricate functionally graded materials (FGMs) with gradually variable composition and structures as a function of position. In this work, a powder-based laser directed energy deposition (LDED) process was carried out to develop a series of compositionally graded joints from 316 stainless steel to Inconel 718 alloy. The microstructure, composition, precipitation transformation and mechanical properties were investigated as a function of position in FGMs via experimental characterization and computational analysis. The 75 wt% IN718 component with fine and equiaxial grains is directly obtained from the laser deposition. The diffusion and segregation of Ni, Nb and Ti elements underly the transformation mechanism between Laves, NbNi3/δ, γ'' and γ'' phases during aging, which has a high consistency with the computational prediction. The precipitation transformation has a close relationship with the final mechanical properties of the FGM. The computational-experimental approach is a promising method to tune the microstructure-property relationship of dissimilar metal joints. The gradient precipitation that can be flexibly tuned by LDED process provides a high throughput design to develop new functional materials with local tailoring of properties.