Microstructural characterization and surface properties of laser clad Ni-ZrB2 coatings on Ti-6Al-4V alloy

Preservation of surface integrity of engineering assets has been achieved by laser cladding of nickel matrix composites in recent years. Ceramic-metal (cermet) coatings offer outstanding surface performances, improved mechanical, thermal and tribological capabilities. In this study, nickel matrix composites with two different compositions of an ultra-high temperature boride reinforcement namely, ZrB2, was considered. Laser cladding of Ni-ZrB2 binary coatings was successful. The microstructural orientation of the coatings was studied as scanning electron microscopy revealed the general transition of mixed cellular grains and dendrites to fine crystals with increasing depth from the free surface towards the substrate. It was observed that the interfacial region of Ni-10% wt. ZrB2 coatings were characterized by smaller cellular grains. Microhardness, oxidation behaviour and tribological tests were conducted on coatings containing 5 and 10% wt. ZrB2. Phase analysis displayed the secondary phases formed within the cermet coatings, which were responsible for the improved microhardness of Ti-6Al-4V alloy. Furthermore, the effect of scanning speed during laser cladding was investigated. Results revealed that Ni-10% wt. ZrB2 fabricated at a deposition speed of 1.2 m/min showed the most suitable surface performance amongst the cermet coatings.