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This work aims to study the influence of heat treatment on the microstructure of laser metal deposited multi-layered Inconel 718 alloy. As-deposited samples were subjected to standard heat treatment, and the resulting microstructure and mechanical properties are studied. When observed under optical microscope and scanning electron microscope, the microstructure revealed microstructural homogenisation. In this case, the grain morphology shows that Nb-rich Laves phase in as-deposited sample is converted to small irregular granules in post heat treatment. The main finding of this study is that after heat treatment, the continuous bands of Nb-rich Laves phase are dissolved into small patches, as observed in elemental mapping through Energy Dispersive Spectroscopy. Also, Nb and Ti are distributed uniformly in the microstructure forming γ´ (Ni3Ti) and γ´´ (Ni3Nb) strengthening precipitates in Ni matrix. The precipitates developed has resulting in 50–60% higher hardness (419 HV) in the heat-treated sample compared to as-deposited sample. [ABSTRACT FROM AUTHOR]

Direct metal deposition (DMD) technique results in unique microstructure when compared with the traditional manufacturing processes because of rapid solidification and the combined effect of input process parameters. However, parametric effect on the microstructure evolution is not thoroughly understood. This paper deals with the investigations carried to understand the effect of process parameters on the microstructure characteristics of Inconel 718 deposits fabricated by DMD process. The microstructure observations revealed columnar dendrites at the bottom, middle portions, and equiaxed grains in the top portion of the deposits. The different grain morphologies obtained are primarily due to the interaction effect of thermal gradient and solidification velocity. Furthermore, analysis is carried on the microstructural characteristics, and cooling rates during solidification were evaluated. It was observed that the cooling rates are varying systematically with input parameters. In addition, the grain size is observed to be a function of cooling rate. EDS analysis performed on the deposits, where the elemental mapping revealed long chains of Nb-rich phases at the interdendritic regions. The microhardness measurements done using Vickers indentation method show a minimal variation with process parameters; the hardness followed a linear relationship with the reciprocal square root of grain width. [ABSTRACT FROM AUTHOR]