Microstructures, mechanical properties and corrosion resistance of Hastelloy C22 coating produced by laser cladding

The Hastelloy C22 coatings H1 and H2 were prepared by laser cladding technique with laser scanning speeds of 6 and 12 mm/s, respectively. Their microstructures, mechanical properties and corrosion resistance were investigated. The microstructures and phase compositions were studied by metallurgical microscope, scanning electron microscope and X-ray diffraction analysis. The hardness and scratch resistance were measured by micro-hardness and nanoindentation tests. The polarization curves and electrochemical impedance spectroscopy were tested by electrochemical workstation. Planar, cellular and dendritic solidifications were observed in the coating cross-sections. The coatings metallurgically well-bonded with the substrate are mainly composed of primary phase γ-nickel with solution of Fe, W, Cr and grain boundary precipitate of Mo6Ni6C. The hardness and corrosion resistance of steel substrate are significantly improved by laser cladding Hastelloy C22 coating. Coating H2 shows higher micro-hardness than that of H1 by 34% and it also exhibits better corrosion resistance. The results indicate that the increase of laser scanning speed improves the microstuctures, mechanical properties and corrosion resistance of Hastelloy C22 coating.

► Hastelloy C22 coatings were prepared by diode laser cladding technique.
► Higher laser speed resulted in smaller grain size.
► Size-effect played the key role in the hardness measurements by different ways.
► Coating with higher laser scanning speed displayed higher nano-scratch resistance.
► Small grain size was beneficial for improvement of coating corrosion resistance.