Parametric study on laser additive manufacturing and subsequent post processing of inconel 718 thin walled structures

Laser Additive Manufacturing (LAM) is one of the greener routes for fabrication of Inconel 718 (IN718) components. In the present work, Taguchi L9 array based optimization is performed using grey relational analysis to optimize the process parameters for the fabrication of thin walled structures using a 2 kW fibre laser based additive manufacturing system. Within the framework of the experimental conditions of the study, the LAM processing parameters, i.e., laser power, scan speed and powder feed rate, are optimized for minimum width and maximum height. The optimized parameters are used for the deposition of multi-layered walls and it is subjected to heat treatment at 1000 °C for duration of one-hour, followed by water quenching. Comprehensive investigations on microstructural and mechanical behaviour using optical microscopy (OM), X-ray diffraction (XRD) analysis, micro-hardness and automated ball indentation (ABI) are carried out. Microstructure examinations of LAM deposits of IN718 reveal intermixed dendritic and cellular structures. However, homogenization in microstructure is observed through heat treatment resulting in reduced micro-hardness. It is also observed that there is considerable increase in the crystallite size of the deposits after heat treatment. This study opens a new route for fabrication of thin walled structures using LAM with modified properties by erasing the thermal history through heat treatment.