Microstructure and wear behaviors of laser cladding in-situ synthetic (TiBx+TiC)/(Ti2Ni+TiNi) gradient composite coatings

TiNi/Ti2Ni-based gradient composite coatings reinforced with TiC and TiBx were produced on TC4 substrates by laser cladding with different composition powder mixture (10B4C+90TiNi, 20B4C+80TiNi, 30B4C+70TiNi, wt.%) prepasted to improve the surface wear resistance under different service conditions. A large amount of TiB and TiB2 as well as a bulk eutectic structure of TiB2+TiC were in situ formatted in the gradient composite coatings. The rod-like TiB in the single-layer coating changed to the slender needle-like TiB in the double-layer gradient coating, and the coarse rod-shaped TiB2 became the major reinforcement in the working layer of the triple-layer gradient coating. The changes of the morphologies and sizes of the reinforcements in the working layers made the microhardness of the coating up to 1555.1 HV0.2, which was 4.6 times that of the substrate (340 HV0.2). From the results of the dry sliding wear tests, the coefficient of friction of the coatings (0.30–0.45) were considerably lower than that of the substrate (0.45–0.55) and the wear mass loss of coatings had more than 50% reduction compared with that of the substrate (3.2 × 10−3 g).