Microstructure Evolution and Mechanical Behavior of Inconel 625 Produced Using Direct Laser Metal Deposition

The microstructure and mechanical behavior of Inconel 625 superalloy manufactured by additive manufacturing technology direct laser metal deposition (DLMD) technology and then subjected to anneal heat treatment under three different temperatures (1000, 1100, 1200 degrees C) were studied. In this study, some cylinder-shaped objects were fabricated by the high-power pulse wave fiber laser,-without cracks, interfacial defects, or porosity. Then the scanning electron microscopy (SEM) and transmission electron microscopy (TEM) were employed to analyze their microstructure. It is found that some Laves phase precipitated in the interdendritic region results from the segregation of niobium and molybdenum. The thermal stability of a structure of dendritic morphology was investigated through annealing of the specimens at the temperature range from 1000 to 1200 degrees C. The precipitated carbides have two types, ellipsoid type of NbC and block-shape type characteristic of Nb(Ti)C. Moreover, the morphology of Laves phase changes from irregular shape to short rod-like one or bulk shape. With the temperature of annealing increasing from 1000 to 1200 degrees C, the Laves phase partially dissolves into the gamma-Ni matrix and results in the recrystallized large grains. Results of tensile process show that a higher tensile strength and elongation are obtained for the annealing specimens when compared to the as-deposited samples.