Cold metal arc transfer (CMT) metal deposition of Inconel 625 superalloy on 316L austenitic stainless steel: microstructural evaluation, corrosion and wear resistance properties

The low dilution cladding process, Cold metal arc transfer (CMT) is an modified version of conventional GMAW welding process with the advantage of controlled heat input was carried out for studying the microstructural, corrosion and wear behaviour of Inconel 625 superalloy. The CMT cladding, in addition can be used as a repair method for any type of alloy. The base material used here is 316 L and the corresponding filler wire is Inconel 625. The input parameters considered were welding current (120, 160, 200 Amps), voltage (15, 19, 20 volts), torch angle (50, 70, 90 degrees) and travel speed (100, 150, 200 mm min−1). The microstructure was examined using optical microscopy, scanning electron microscopy (with energy dispersive x-ray analysis) and x-ray diffraction analysis. The Inconel 625 clad beads are free from pores and cracks and are well bonded with minimal dilution. The heat input has a linear relation with the wire feed and speed during the cladding process. The clad beads contain dendritic and interdendritic precipitates containing Mo and Nb growing vertically along the substrate. The intermetallic precipitates combine into columnar dendrites near the topmost region of the clad along with the formation of γ, the Laves and (Nb, Ti) C phases. The EDS curve indicates the presence of low Fe concentration in the Inconel 625 alloy cladding. The corrosion performance of the clad region nearer to interface region and higher to substrate in 3.5 wt% NaCl solution, indicating an excellent protection for Inconel 625. The as deposited cladding is composed of the Ni-rich γ (Ni, Fe) phase, M23C6, Ni3B, and Ni3Si. At the applied load of 90 N, the wear rate gets doubled than the rates under loads of 20 N and 50 N. The wear mechanism tends to vary with the wearing time and the load applied. The outcome of this study reveals that the relatively new CMT process, with the suitable process parameters, would be apt for build up of affected areas of worn out and service damaged components of gas turbines applications.