Abstract:Utilizing self-propagating high-temperature synthesis (SHS) reactive spraying technology, the feeding self-combustion agglomerated particles composed of Ti, B₄C and C powders, TiC-TiB₂ multi-phase ceramic coatings were prepared on the steel substrates. Orthogonal experiment was carried out to optimize the spraying parameters. The phase component and microstructure of the coating fabricated at the optimized parameters were studied by XRD and SEM. The reactive mechanism in flying agglomerated particles was discussed. The optimized conditions, spraying distance of 220 mm, powders delivering gas pressure of 0.3 MPa and preheating temperature of 240 ˚C to sprayed particles, were obtained from orthogonal experiment. For the coating, porosity of 2.5% and HV 1 595 are achieved under the optimized parameters. The coatings are mainly composed of TiC_0.3N_0.7, TiB₂ and a little TiO₂. The SEM analysis shows the morphology of TiC_0.3N_0.7 matrix in which the fine granular TiB₂ crystals evenly disperse. It is concluded that, as solo reactive units, the agglomerated particles would finally form into the coatings after going through four successive stages in the flame, which are, respectively, pregnant reaction, flight combustion, collision and structure transformation and solidification. The solid diffusion and dissolution-precipitation are the two mechanisms to control the synthesis reaction.

Key words: TiC-TiB₂ ceramic coating; SHS reactive spraying; orthogonal experiment; reactive mechanism