Structural-phase and tribo-corrosion properties of composite Ti3SiC2/TiC MAX-phase coatings: an experimental approach to strengthening by thermal annealing

Composite Ti3SiC2/TiC MAX-phase coating was obtained by the detonation spraying onto U9 steel substrate using the mixed powder in the molar ratio of 74Ti/20SiC/6C as raw material. At the as-sprayed state, the synthesized composite had a stable double-phase composition: the main TiC phase and secondary Ti3SiC2 MAX-phase. After thermal annealing at 700, 800 and 900 °C, oxidation occurred in the coatings, as indicated by the appearance of high-temperature-stable anatase TiO2 phase at the diffraction patterns. It was found that annealed at 800 °C coating demonstrated the best structural, compositional, tribo-mechanical and corrosion resistance characteristics. In particular, hardness increased to 1400 ± 75HV0.2, coefficient of friction decreased to 0.35, adhesion strength was 14 N, and corrosion potential was 1.88 × 10−2 A/cm2. The corrosion potential of the annealed composite was 5.5 times less than that of the steel substrate, which indicates its strong corrosion protection. The relatively higher density, the formation of the main TiC phase that inhibits the grain growth and TiO2 thin surface layer that serves as good diffusion barriers were the main reasons for the improvement of the functional parameters.