Microstructural change during laser welding of Inconel 718

Abstract

In this study, Inconel 718 superalloy has been subjected to laser welding using a 2 kW continuous wave (CW) Yb-Fibre laser at a constant power of 1800 W with a varied scan speed of 1400 mm/min, 1200 mm/min, and 1000 mm/min, respectively. The effect of process parameters on microstructure, and microhardnes and nano-mechanical property has been studied. There is formation of reinforcement on the face of the weld zone and sometimes in the root. The weld reinforcement height has been found to vary from 51.3 μm to 72.9 μm and increases with increase in scan speed of laser beam. The microstructure of the weld zone is fine columnar in the solid liquid interface followed by dendritic region and with equiaxed morphology in the middle. In the inter-columnar, interdendritic or grain boundary regions there are presence of gamma and gamma prime precipitates. The orientation of grains in terms of micro-texture has been carefully analysed by EBSD analysis. The texture of the weld zone is marginally different from that of the base metal. There is a marginal decrease in microhardness (from 280 VHN for as-received to 246 VHN) in laser welded Inconel 718. A detailed nano-mechanical property of the weld zone has been studied by nano-hardness measurement.