Investigation On The Reactive Plasma Sprayed Nanostructured Aluminium Nitride/Titanium Nitride Multi-Phases Coatings

In this paper, nanostructured multi-phases coatings was fabricated by sprayed Ti-Al mixed-powders, via reactive plasma spraying (RPS), using the self-designed gas-tunnel type reaction camber. The parameters of reactive plasma spraying TiN coatings have optimized, the mechanical and tribological properties of the multi-phases coatings were investigated, and the formation mechanism of the multi-phases coatings was discussed.During the optimizing reactive plasma spraying TiN coatings, it was found that coatings in which TiN phase acts as mean phase could be fabricated within the scope of wide plasma power. After comprehensive considerations in influence of spraying parameters on phases, microstructure and microhardness of TiN coatings, the optimizing spraying parameters could be obtained: plasma power being 36~40kW, spraying distance being 20~30mm, the N2 gas flow rate in the reaction chamber being 2.5m3/h, ion-gases proportion N2/Ar being 2 : 3~1 I 1.Experimental results show that reactive plasma spraying multi-phases coatings mainly contained TiN which is the main phase, AlN, Al3Ti, Ti3O, etc. The cross-sectional micro-hardness of the multi-phases coatings could be maximized to HV2065.4. TEM analysis indicated that multi-phases coatings were composed of nano-scaled crystal grains ranging from 50 to 80 nm. AlN crystal grains ranging from 10 to 30 nm were distributed in multi-phases coatings.The wear-resistance of reactive plasma spraying AlN/TiN multi-phases coatings is higher than that of TiN coatings under the unlubricated condition, which was about 1.3 times than TiN coatings under high load. The antifriction performance of multi-phases coatings is also more excellent than TiN coatings.The TiN formation is mainly combustion synthesis with molten Ti in the N2 gas in the process of reactive plasma spraying AlN/TiN multi-phases coatings, which belongs to surface combustion reaction of gas penetration combustion. Combustion mechanism is that reaction can be proceeded by reaction formation of TiN product layers between Ti and N2. The AlN formation is plasma assisted chemical vapour deposition (PACVD) that is proceeded between vapor of Al powders and N2 gas in plasma gun, which belongs to high temperature vapor phase synthesis. Al3Ti is formed by reaction between molten Al and Ti.