Microstructure and wear properties of multi ceramics reinforced metal-matrix composite coatings on Ti-6Al-4V alloy fabricated by laser surface alloying

To improve the wear resistance of titanium alloy, self-lubricating metal-matrix composite coatings reinforced by multi ceramic phases were designed and fabricated by laser surface alloying with the mixed powders of Ni, B4C, graphite and Si3N4 on Ti-6Al-4V alloy. Microstructure and wear resistance of the coatings were investigated. The coatings were mainly composed of TiB2, SiC, TiC0.7N0.3 and the phases containing Ni. There was residual graphite in the coatings. The average hardness of the coatings was 1385-1687 HV, equivalent to 3.7-4.5 times of the substrate. The coatings displayed superior wear resistance under dry sliding wear test condition at room temperature, compared to the substrate (over 13 times better than the substrate). The coating fabricated with the mixed powders of Ni:B4C:C(graphite):Si3N4 = 1:1:1.5:0.2 (mole ratio) exhibited the best wear resistance due to the good matching relationship of the high hardness, good lubrication and certain toughness. The wear mechanism of the coatings was discussed.