Parametric effect on the microstructure of direct metal deposited Inconel 718

ABSTRACT

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.

KEYWORDS:

• Direct metal deposition
• grain morphology
• cooling rate
• elemental segregation
• microhardness

Disclosure statement

No potential conflict of interest was reported by the author(s).

Additional information

Funding

This work was supported by the Department of Science and Technology, Ministry of Science and Technology [DST/TDT/AMT/2017115(C)].