Microstructure and Tribological Performance of Laser-Cladded Ni60+h-BN Coatings on Ti-6Al-4V Alloy at High Temperature

Abstract

With the expansion of the application range of titanium alloys, the wear protection problem has become increasing prominent due to their poor wear resistance, especially in high-temperature environments. To solve this problem, in this work, Ni60+h-BN coatings on Ti-6Al-4V (TC4) alloys were prepared using a laser cladding technique. The results indicated that the Ni60+h-BN coatings mainly contain the phases of NiTi2, TiN, TiB, (Si, Al)2Cr, and solid solution Fe0.2Ni4.8Ti5, possessing much higher microhardness (1,055.36 ± 16.33 HV0.22) than TC4 substrates (309 ± 10 HV0.2), and the Ni60+h-BN coatings show excellent wear resistance and antifriction properties at 600 °C with the dominant wear mechanism of slight adhesive wear and oxidative wear. As observed by X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDS) analyses, most of the initial h-BN particles in the mixed powders were decomposed and the reinforcements of TiB and TiN were in situ synthesized after high-power laser irradiation, which plays a role in wear resistance, and the metal oxides (TiO2, Al2O3, NiO, and Fe2O3) produced under high-temperature friction condition play a role in lubrication and antifriction at 600 °C. As a consequence, the synergy effect of coupling the reinforcements and the metal oxides contributes to the excellent tribological performance of Ni60+h-BN coatings at 600 °C.