Microstructure and corrosion behavior of high power diode laser deposited Inconel 625 coatings

Abstract

A series of experiments were performed to investigate the one-step laser cladding of Inconel 625 powder, injected off-axially onto mild steel substrates. The experiments were carried out using a 6 kW high power diode laser mounted to a six axis robot system. The rectangular shape of the delivering beam was focused to a spot size of 22 mm×5 mm on the work piece. The powder feeding head, which consisted of a cyclone and flat nozzle, spread the powder stream to a spot size used. The coating samples were produced using different levels of powder feed rate (77–113 g/min), constant traveling speed of 400 mm/min, and laser power of 6 kW. Powder and laser-clad coating microstructures were studied by x-ray diffraction, scanning electron, and optical microscopy. The coating microstructure was found to consist of a directionally solidified single phase (highly alloyed Ni), face-centered cubic structure with a lattice parameter of 0.3596 nm. The corrosion resistance of the one-step laser-clad coatings was tested in 3.5 wt % NaCl using electrochemical methods. Laser-clad coating was compared with wrought Inconel 625 alloy, high-velocity oxy-fuel sprayed, and plasma transferred arc welded coatings. The corrosion resistance of laser-clad coatings was found to be equivalent to corresponding bulk material and superior to sprayed and welded coatings.