Researches On High-temperature Friction And Wear Behavior Of Vanadium-base Coatings

With the rapid development of high-tech,the working temperature of moving parts in many types of equipment is getting higher,which is growing demanding for new self-lubricating coatings.The vanadium-base coating has excellent lubricity at high temperatures and can adequately protect the substrate.Based on this,we did researches on the high-temperature friction and wear properties of vanadium-based coatings.In this paper,VAlCN composite coating,VAlCN/VAlN multilayer coating,and VAlN-Ag composite coating were prepared by direct current magnetron sputtering?DCMS?.The failure mechanism of VAlCN coating and the relationship between oxidation performance and friction performance of VAlCN/VAlN multilayer coating were systematically studied.In order to further enhance the lubrication of the coating,the high-temperature friction properties of the VAlN-Ag composite coating were initially explored.The main conclusions obtained are as follows:?1?The friction coefficients of single-layer VAlCN composite coating prepared by DCMS are high.The wear rate of the coating increases with increasing temperature,and the coating quickly fails at 700°C.According to the morphology of the wear track,the coating has outstanding oxidation resistance below 400°C,and the wear rate is low.The main wear model is slight adhesive wear.Above 500°C,due to the increase of oxides,the coating wear model is transformed into abrasive wear and oxidative wear.The coating quickly fails at 700°C,mainly due to the melting of a large amount of Vanadium-containing oxide in the coating and the failure of the coating after amorphous carbon be oxidated.Although the friction coefficient is reduced to 0.2 at this temperature due to the melted of V₂O₅,lubrication cannot be continuously provided after the melted V₂O₅ is consumed.?2?The VAlCN/VAlN multilayer composite coating prepared by DCMS significantly improved the oxidation resistance of the coating compared to the single-layer VAlCN coating.The multilayer coating maintains a clear multilayer structure at 500°C.Therefore,the main wear model of the coating is layer-by-layer wear below 500°C.Coatings above 600°C produce a variety of oxides due to complex tribo-oxidation,which exhibit a mix model including abrasive wear,oxidative wear,fatigue wear,and adhesive wear.?3?Since Ag has a high sputtering yield,the VAlN-Ag composite coating containing more Ag is thicker.However,the excessive growth rate of the coating causes the coating has a coarse columnar structure.Meanwhile,the higher the Ag content,the worse the mechanical properties of the coating.High-temperature wear tests show that Ag particles have a strong ability to diffuse to the surface,but the coating has a significant lubricating effect only at 350°C and 700°C.Although the coating wear is severe at 700°C.Since the wear debris accumulates on the ball,the direct contact between the grinding ball and the substrate is isolated,and the friction coefficient is always low,about 0.2.?4?The friction and wear mechanisms of coatings at different temperatures are entirely different.Due to the oxidation of the coating,the structural evolution at high temperatures,the attenuation of mechanical properties and the formation of tribo-oxidation products directly affect the high-temperature friction properties of the coating.