Corrosion and wear behavior of laser cladded Ni–WC coatings

Abstract

A nickel–tungsten carbide (Ni–WC) composite is an ideal protective coating for a harsh environment. In this study, the corrosion and wear behavior of a laser cladded Ni–WC coating fabricated by a high power direct diode laser (HPDDL) with different chemical compositions was investigated. In the modified Ni–60%WC, the chemical compositions were enhanced by the addition of lanthanum oxide (La2O3) and molybdenum and by replacing a portion of micro-sized WC with nano-WC particles. The corrosive resistance of the coatings was investigated utilizing potentiodynamic polarization, long-term immersion tests, and surface analytical techniques. The corresponding wear response was studied by using a dry unidirectional sliding wear test according to the ASTM G99 standard. Modification of the laser-cladded coatings was interpreted on the basis of its microstructure, microhardness, and phases of chemical composition. It has been observed that an optimal addition of nano-WC (5wt.%), La2O3 (1wt.%), and Mo (1wt.%) refines the grain size of the Ni binder and improves hardness, passivation capability of the coating under corrosion, and wear resistance. The pitting corrosive resistance of the modified coatings was enhanced due to a higher chemical stability, a more uniform surface potential, and a higher passivation capability.