Study On Preparation Of Ternary Boride Coating And Its Al-Si Corrosion And Wear Resistance

The hot dip plating process is one of the main methods for corrosion protection of steel materials,with the advantages of low cost and high corrosion resistance.However,the sink/stabilizing rolls working in high temperature plating solution are not only corroded by the plating solution,but also subjected to the frictional wear effect between the strip steels,which makes them fail prematurely.Ternary boride coatings have excellent properties such as high temperature resistance,metal melt corrosion resistance and wear resistance,which have high potential for application in the field of hot dip plating.In this paper,CoMoB and CoWB-based ternary borides were selected as the research objects,and WC-WB-CoCr and MoB-CoCr coatings were prepared by HVOF technology.The effects of spraying parameters on the organization of the coatings and their mechanical properties were investigated;the resistance to aluminum-silicon corrosion and high-temperature frictional wear properties of coatings were studied;the effects of CeO₂ on the organization,mechanical properties,corrosion resistance and high-temperature wear performance of MoB-CoCr coatings were investigated.The results of the study are as follows:（1）The main physical phases of the WC-WB-CoCr coating consisted of CoW₂B₂,WC and Co₆W₆C.The optimum kerosene flow rate and spraying distance were 32 L/h and 360 mm.The obtained coating porosity was 0.41%and Vickers hardness was 1176HV_0.3.After the molten Al-Si corrosion test,the failure of WC-WB-CoCr coating was mainly in the form of oxidation and cracking of the coating,and the coating failed rapidly when the corrosion temperature was increased to 740°C.The high temperature wear mechanisms of coatings are mainly oxidation wear,fatigue wear and adhesive wear.The oxide film on the surface of the wear track is mainly composed of WO₃ and CoWO₄.CoWO₄ shows better high temperature wear resistance than WO₃.With the increase of the test temperature,the wear rate of the coating increases with the increase of the temperature,but the increase of the wear rate decreases with the increase of the temperature.（2）The main phase of MoB-CoCr coating consists of ternary borides CoMo₂B₂,CoMoB and binary borides MoB and Cr B phases.The porosity of the coating is 0.95%,and the Vickers hardness of the coating is 929 HV_0.3.After the molten Al Si corrosion test,the MoB-CoCr coating was subjected to uniform corrosion of liquid Al Si alloy,and the corrosion products were mainly（Mo,Cr）（Al,Si）₂,（Co,Cr）Al₉ and MoB₂.（Co,Cr）Al₉ is mainly concentrated on the outer side of the corrosion layer and（Mo,Cr）（Al,Si）₂ is mainly concentrated on the inner side of the corrosion layer.Temperature greatly affects the corrosion rate of MoB/CoCr coatings,and the thickness of the corrosion layer increases parabolically with the extension of corrosion time.The failure mechanism of the MoB-CoCr coating is mainly the decomposition of ternary borides and the reaction diffusion of aluminum and silicon atoms to the inside of the coating.MoB-CoCr coating exhibits excellent high temperature wear resistance.The oxide film composed of MoO₃,CoMoO₄ and Cr O₃ is formed on the surface,which can significantly reduce the friction coefficient and wear rate of the coating at high temperature.The wear mechanism of the coating at 680°C is mainly grain-abrasion wear and oxidation wear.With the increase of temperature and the increase of oxidation,the wear mechanism of the coating is transformed into oxidation wear and adhesive wear.（3）The addition of CeO₂ had no significant effect on the physical phase of the MoB-CoCr coating,and CeO₂ exists in the form of crystalline CeO₂ and amorphous Ce-O-B in the coating.With the increase of CeO₂ content,the pores of the coating decreased first and then increased.The coating with 3 wt.%CeO₂ had the densest structure,the porosity of the coating was 0.61%,and the hardness was 1025 HV_0.3.After the molten Al-Si corrosion test,the coating with 4 wt.%CeO₂ had the best Al-Si corrosion resistance.This is because Ce-O-B amorphous phase will be formed at the junction of CeO₂ and MoB-CoCr coating,where the diffusion of Al and Si atoms is difficult and complex.In addition,crystalline CeO₂ itself can act as a physical barrier during the corrosion process,hindering the diffusion of corrosion elements.With the increase of CeO₂ content,the coating wear first decreases and then increases,and the coating doped with 3 wt.%CeO₂ has lower wear rate,which is because the coating doped with 3 wt.%CeO₂ has the densest structure and has better wear resistance.