THE PERFORMANCES OF TiN-TiB₂ COATING PREPARED BY REACTIVE PLASMA SPRAYING

Reactive plasma sprayed coatings were prepared on carbon steel substrates with Ti and B₄C as starting materials. Two kinds of gases (Ar and N₂) were used as feeding gases for powders, respectively. 10 wt.% Cr was added in the powders as binder to increase the bond strength of the coating. The phases, microstructure, micro-hardness and corrosion polarization behavior in 3.5 wt.% NaCl solution of the two coatings were studied. The results show that TiN-TiB₂ coatings were prepared under both conditions. The two coatings have typically laminated structure. However, the coating prepared with Ar as feeding gas has higher porosity and some unmelted Cr particles. It also contains certain content of titanium oxides. The microhardness of coating prepared with Ar as feeding gas is lower due to its higher porosity, unmelted Cr particles and some amounts of TiO₂. The corrosion resistance of TiN-TiB₂ coating prepared with Ar as feeding gas in 3.5 wt.% NaCl solution is worse than that of the coating prepared with N₂ as feeding gas. Yet the corrosion resistance of reactive plasma sprayed TiN-TiB₂ coating is improved greatly compared with that of carbon steel. The thermodynamic analysis of reactive plasma spraying process is also discussed.