Study On VAlTiCrW Based High Entropy Alloy Coating Of Preparation And High Temperature Tribological Properties Properties

With the rapid development of science and technology and the increasing requirements of national aerospace for high-temperature wear-resistant materials,traditional alloy materials often can not meet the needs of practical application.Therefore,new high entropy alloy materials came into being.High entropy alloy coating has similar comprehensive properties to bulk materials and simple preparation method,which has attracted extensive attention of scholars.In this paper,VAlTiCrW based high entropy alloy coating was prepared at 100℃ by magnetron sputtering technology,which can effectively control the composition of high entropy alloy and composite target,and its high-temperature tribological properties were investigated in detail.The main research contents are as follows:（1）Firstly,the phase formation of VAlTiCrW high entropy alloy coating is judged by mixing entropy,mixing enthalpy,mean square deviation of atomic radius and valence electron concentration.The results show that it has uniform element distribution and BCC phase structure.At the same time,the coating has good lubrication characteristics at high temperature:in the friction test at 800℃,there is an obvious V precipitate phase,which is magnéli oxide phase and leads to low friction performance.At this time,the friction coefficient of the film decreases to 0.19.After heat treatment at 800℃and Tribological test at 700℃,the friction coefficient can also be maintained at 0.2.It is not the dominant role of V₂O₅ in the relevant literature,but the new lubricating phase AlV₃O₉ with layered structure plays a role in the microstructure.The lubricated mechanism at high temperature may be similar to MoS₂,but it does not rule out the low friction coefficient caused by the softening of the material.（2）Under the same preparation conditions,（VAlTiCrW）O_x coatings with different oxygen content were obtained by changing the oxygen flow rate.With the increase of oxygen content in the coating,the coating structure changes from BCC to amorphous structure,and its roughness decreases from 56.9 nm to 11.3 nm;At the same time,with the increase of oxygen content,the hardness of the coating first increases and then decreases.When the oxygen flow is 10 sccm,the hardness of （VAlTiCrW）O_x coating is as high as 11.9 GPa,and it has a low friction coefficient at 700℃;However,its adhesion decreases gradually,and the coating becomes hard and brittle,which is not conducive to wear,and even peeling marks appear.In addition,the results of 3.5 wt% NaCl solution electrochemical test indication that the self corrosion current density of oxygen doped coating is 7 times lower than that of non oxygen doped coating.In the electrochemical test results in acidic 0.5 mol/L H₂SO₄ solution,the self corrosion current density of doped oxygen coating is two orders of magnitude lower than that of undoped oxygen coating,which indicate doping oxygen enhance high entropy alloys of corrosion resistance.（3）In order to investigate the application of（VAlTiCrW）O_x high entropy alloy coating under actual working conditions,by transformation of the friction testing machine,the tribological properties of the coating on the brush wire sealing device of aerospace engine were simulated and evaluated by means of brush wire tribological.The experimental results show that the （VAlTiCrW）O_x high entropy alloy coating prepared when the oxygen flow rate is 10sccm has low friction coefficient and wear rate,and has good brush wire tribological properties.The realization of low friction is related to V₂O₅ formed by in-situ oxidation of the coating at high temperature,and the reduction of wear rate is related to the hardness of the coating itself and the formation of WO₃,Cr₂O₃,Al₂O₃ and AlVO₄ hard phases in surface at high temperature.