| As a novel alloy material,high-entropy alloys(HEA)have attracted wide attentions due to the high strength,excellent corrosion and oxidation resistance.By combining with the surface coating technology,the invention of high-entropy alloy coatings provides a new method to improve the performance of marine materials.For starters,the V-Al-Ti-Cr-Si composite target was designed,and then VAlTiCrSi high entropy alloy film was prepared by DC magnetron sputtering technology,simultaneously the preparation process being optimized in this paper.And the thermal stability,frictional performance at high temperature and corrosion resistance in artificial seawater of HEA films were systematically studied.At the same time,the passivation behavior and corrosion mechanism of high entropy alloy films were analyzed in detail by means of the constant potential polarization,XPS and TEM technology.Through the vacuum annealing experiments,the phase change occurred during the high temperature friction tests of VAlTiCrSi HEA films was simulated to investigate the high-temperature frictional mechanism combined with the corresponding characterization of the annealed films.The VAlTiCrSi high-entropy alloy films in the amorphous state were successfully prepared by the magnetron sputtering technology using the self-designed V-Al-Ti-Cr-Si composite target arranged in a periodic manner.The HEA films sputtered at bias voltage of-50 V,which is the best preparation parameter,has a smooth and dense surface and a uniform composition distribution.The high-entropy alloy films show a better corrosion resistance than 304 stainless steel in the artificial seawater.The corrosion current density of the HEA films reached 4.68×10-9 A/cm2,an order of magnitude lower than that of 304 stainless steel(5.44×10-8 A/cm2),and the HEA films have a wider passive region compared to 304 stainless steel.In addition,the passive film on the surface of HEA film have a good stability in artificial seawater.In order to further investigate the passive film on the surface of VAlTiCrSi high-entropy alloy film,a single layer amorphous passive film with the thickness of about 10nm was obtained after constant-potential polarization treatment.The passive film has a homogeneous composition distribution and covers the whole HEA film continuously and completely.The XPS results display that the passive film is mainly composed of the oxides of V,Al,Ti,Cr and Si and free state(M0)of each element.In combination with PDM theory,it is revealed that the excellent corrosion-resistance of the passive film is attributed to its complex composition.Based on the characterization of the corroded HEA films,it is found that during the rupture process of the passive film,the chloride ions mainly react with Cr element,and other elements besides Cr element work against the rupture of the passive film in some sense.As a result,the corrosion-resistance of VAlTiCrSi HEA film is better than that of 304stainless steel.VAlTiCrSi high entropy alloy films display an excellent high-temperature frictional performance and thermal stability.The results of high-temperature friction experiments manifest that the temperature corresponding to the lowest frictional coefficient and the best abrasive resistance of VAlTiCrSi HEA films is at 700?.The experimental results by simulating phase changes reveal that the main reason for the excellent frictional performance of HEA films at 700?is the phase structure transformation.At 700?,the constituent phase of the HEA film transforms from totally amorphous state to the coexistence of BCC solid solution phase,Al8Cr5 phase,(V,Ti,Cr)5Si3 phase and amorphous phase.After the phase structure transformation,the mechanical properties of HEA films are improved obviously,which correspondingly enhances the abrasive resistance and frictional performance of HEA films.Simultaneously,the phase structure where the solid solution coexist with the intermetallic compounds also significantly improves the abrasive resistance of VAlTiCrSi high entropy alloy films. |
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