Hierarchical phase evolution during direct laser deposition of an in-situ Ni-NbC composite

Abstract

Direct laser deposition of a mixture of 90 wt.% nickel (Ni) and 10 wt.% niobium-carbide (NbC) using the laser engineered net shaping process resulted in the formation of an in-situ Ni-NbC composite with a complex hierarchical multi-phase microstructure. Detailed microstructural characterization at multiple length scales revealed that the in-situ composite consisted of a primary dendritic Ni-rich γ phase with an interdendritic γ + NbC eutectic. The interdendritic eutectic γ phase further decomposes via discontinuous precipitation into a lamellar mixture of γ + δ phase (Ni3Nb). The sequence of phase evolution in this complex hierarchical in-situ composite system has also been established in the present study.