| The ingots and workpieces of various alloys are faced with serious oxidation problems during high temperature hot working.Most titanium alloy ingots need to be homogenized at Tβ+150-200 ℃ for a long time before cogging.Solving the problem of high temperature oxidation in the hot working process of titanium alloy can greatly improve the yield of titanium alloy workpieces and lay the foundation of continuous casting and rolling process.Compared with heating in vacuum or protective atmosphere,heat treatment protective coating is more economical and feasible.There is no coating like enamel coating,which has a series of properties such as oxidation resistance,heat insulation,high temperature lubrication,low temperature self-peeling and so on.In this paper,a series of work has been carried out to explore the feasibility and mechanism of enamel coating protecting titanium alloy after heat treatment at 1200 ℃.The microstructure of oxygen rich layer of Ti6Al4 V titanium alloy was characterized by metallographic hardness method.The dynamic curve of oxygen intrusion into the alloy in 5 hours was measured,and the formation process of oxygen rich layer of titanium alloy was clarified.After holding for 5 hours,the oxidation loss of the alloy can reach 2250 μm.A kind of enamel matrix and composite coating for Ti6Al4 V alloy heat treatment at 1200℃ is designed and prepared on the basis of comprehensive literature research.The composite enamel coating can greatly reduce the depth of oxygen intrusion into the alloy.The effects of different post modifiers on the technological properties of enamel slurry and the protective effect of the coating were explored,and the protective mechanism of the coating and the mechanism of self-peeling were conjectured.Through the study of the oxidation resistance of the temporary enamel coating with or without quartz and kaolin,the conjecture about the coating protection mechanism and self-peeling mechanism is demonstrated.The results show that the good protective effect and self-peeling property are due to the alloy/Ti5Si3/Al2O3/enamel multilayer structure formed at the alloy/coating interface.With the addition of quartz and kaolin particles,the composite enamel coating can more effectively prevent oxygen diffusion than the pure enamel coating.The addition of ceramic particles can improve the viscosity of the coated glass phase,reduce the diffusion rate of oxygen in the glass phase,and increase the stability of Al2O3 in the interface layered structure.The effect of different ratio of post-adjusting agent on stabilizing interface and coating structure is studied.Alumina can promote the dissolution of quartz into the glass phase,add a lot of Si and Al elements to the glass network,rapidly improve the viscosity of the coating,reduce the ability of the coating to dissolve Al2O3,and make the coating still peel off after 20 hours of heat preservation.But different from the former,the self-peeling interface here becomes the alloy/Ti5Si3 interface,which is the result of the excellent resistance and diffusion ability of Al2O3 to enlarge the kirkendall effect. |
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