Microstructure evolution and formation mechanism of a crack-free nickel-based superalloy fabricated by laser engineered net shaping

Abstract In this study, the crack-free parts have been successfully fabricated by Laser Engineered Net Shaping (LENS) based on a Ni-Co-Cr-Al-Ti-Fe-Nb-Mo nickel-based superalloy powder, and its microstructure evolution and formation mechanism were investigated. The results revealed that the microstructure along the deposition direction is stray dendrites with disordered growth direction in the bottom two layers, epitaxially growing elongated columnar dendrites dominating the whole cross-section of the as-deposited, fine equiaxed grains in the upper of the last layer, respectively. Moreover, it can be found that although the as-deposited layer contains many high angle grain boundaries, no cracks can be observed. According to the chemical composition and phase analyses, it can be concluded that crack-free microstructure is ascribed to the homogeneous distribution of elements and the formation of single-phase γ in the as-deposited. The effect of 1.34 Al, 1.37 Ti, 0.41 Nb, and 0.50 Mo (wt%) on the formation of low melting point substances is discussed. The room-temperature ultimate tensile strength is about 807 MPa, while the high-temperature ultimate tensile strength is 654 MPa.