Research On Ti Coating Prepared By Low Temperature High Velocity Oxygen Fuel

Ti material has found wide potential applications prospect as protective coating owing to the excellent corrosion resistance. However the deposition of Ti coating was complicatedly applied in vacuum or shrouding inert gas environment due to the strong affinity of Ti to oxygen, nitrogen in air atmosphere, which increased the coating deposition cost and complicated the deposition process. By injecting into a certain flow rate of water and adjusting outlet diameter of combustion chamber, plume characteristic with low temperature and high velocity was realized, which made possible for the deposition of Ti coating in air atmospheric environment.In this paper, Ti coatings were deposited on Q235 steel via Low Temperature High Velocity Oxygen Fuel, and coating microstructure, phase and etc. were characterized by SEM, OP, XRD and XPS respectively. The effects of spray distance, combustion chamber pressure on microstructure, conventional properties, electrochemical and corrosion of immersion were discussed. Finally the densification of Ti coating was carried out by heat treatment. The results were as follows:(1) Dense Ti coating with high performance was obtained when the combustion chamber pressure was over 1.5MPa and the spray distance was 80 mm. The surface roughness for as sprayed Ti coating was over Ral3μm. Coating microstructure revealed the coating was comprised by a loose area at the subsurface and a relatively dense inner coating area, even though individual large pores was observed in Ti coating. Besides, distinct oxidation layer was detected at the interface between particles, which was also verified by phase analysis result. The as sprayed Ti coating had a porosity of 2.6%, an oxygen content of 1.64wt% and the bond strength over 40MPa.(2) Electrochemical corrosion of Ti coating revealed that with the increase of density of Ti coating and decrease of oxygen content, Ti coated Q235 steel showed higher corrosion potential and lower corrosion current. Polishing and sealing were both conducive for Ti coating to the improvement in electrochemical corrosion property. The electrochemical corrosion properties for polished Ti coating with sealed treatment was slightly inferior to bulk Ti material. The immersion test results of Ti coated Q235 steel in artificial seawater for 30 days indicated that red rust was not observed on the surface of Ti coating, verifying the excellent protective performance for Q235 steel.(3) Ti coating heat treated at 800℃for 4 h in Ar shrouding environment revealed the inter-diffusion between coating and substrate and between particles inside coating was occurred, and finally the density of coating was improved. The distinct phase transformation after heat treatment was not observed, analyzed by phase analysis. The bond strength of heat treated Ti coating was as high as 50MPa, and the coating micro-hardness was doubled when compared with as sprayed Ti coating. The electrochemical analysis revealed that the corrosion resistance was improved after heat treatment owing to the slight decrease in corrosion current...