Effects of LaB6 on microstructure evolution and properties of in-situ synthetic TiC+TiBx reinforced titanium matrix composite coatings prepared by laser cladding

Abstract

Different amounts of LaB6 (0, 0.5, 1.0, 1.5, 2.0 and 2.5 wt%) were added into Ti-6Al-4V + B4C powder mixtures for fabricated TiC+TiBx reinforced titanium matrix composite coatings on Ti-6Al-4V surfaces by laser cladding processing. The effects of LaB6 addition on the phase composition, microstructure, microhardness, and wear resistance of the coatings were investigated in detail. XRD and SEM results proved that the coatings mainly comprised three kinds of reinforcements such as granular TiC, rod-like TiB2, and acicular TiB. With LaB6 added, La2O3 formed in the grain boundary of rod-like TiB2 through in-situ reaction and impeded the TiB2 growth. The SEM showed that an appropriate amount (≤2.0 wt%) of LaB6 addition significantly refined the coarse rod-like TiB2 phases that were distributed in the upper area of the coatings, however, the excessive LaB6 (≥2.5 wt%) addition reduced the grains refinement effect. The microhardness of the coating was increased with the microstructure refined. And the coating with 2 wt% LaB6 addition had the highest microhardness (1243.4 HV0.2) which increased to 1.23 times more than that of the coating without LaB6 addition, while the wear mass loss was the least (0.97 × 10−3 g) which decreased to 29.3% that of the coating without LaB6 addition.