Investigation of microstructure, mechanical, and corrosion properties of Inconel 617 joints welded by laser–MIG hybrid welding

Abstract

The demand for Nickel-based superalloy of Inconel 617 material is increasing for manufacturing hot section components of gas turbines, chemical, and nuclear power plants. It has excellent corrosion resistance in high-temperature environments. In the present study, laser–MIG hybrid welding consisting of a 3.5 kW CO2 laser in combination with a MIG welding system was utilized to weld 10 mm thick Inconel 617 plates with the wire feed rates (WFR) of 10 and 11 m/min in a single pass to analyze the welds microstructure, mechanical, and corrosion properties. The results revealed that the microstructure of the weld zone is composed of cellular crystals with dendrites and equiaxed sub-grains. Electron backscattered diffraction (EBSD) studies revealed coarse columnar dendrites and equiaxed grains at the center of weld joints with the same crystallographic orientation across the fusion boundary. The XRD analysis revealed the dominant gamma and gamma prime (γ/γ′) [(Ni/Ni3(AlTi))] phases along with the presence of minor carbide peaks such as Ti (C, N), M23C6, Cr (C, N), and M6C. The BM has a lower hardness (232 HV) and higher impact energy (236 J) than the weld joints. Similarly, the increase in WFR results in a decrease in microhardness (268–256 HV) values and an increase in impact energy (199–212 J). The weld joints exhibit good bend ductility without any cracks. The potentiodynamic polarization results revealed a lower corrosion rate of 0.212 mpy for the base metal than for the weld joints. The increase of WFR increased the weld metal corrosion rate from 0.342 to 0.427 mpy due to an increase in heat input (0.516–0.615 kJ/mm) and solidification time, which caused the coarsening of the grains resulting in lower grain boundary density and anode reaction to accelerate, which deteriorated the corrosion resistance of the welds.