| With the gradual development of marine development from offshore to deepsea,aluminum alloy,which is the first choice of lightweight materials,has a broad application prospect in marine equipment.However,aluminum alloy generally has the disadvantages of low hardness and easy pitting corrosion.Especially when the aluminum alloy is used as a moving part of marine equipment,its wear and corrosion resistance(tribocorrosion for short)deteriorate.In addition,the limited information on the tribocorrosion mechanism and quantitative tribocorrosion rate of aluminum alloy in the marine environment seriously restrict the popularization and application of aluminum alloy in marine engineering equipment.Using surface modification technology to improve aluminum alloy’s wear and corrosion resistance has become one of the research hotspots.Focus on the key scientific issues,the interaction between mechanics,chemistry,and electrochemistry in the tribocorrosion process of 7075-T6 aluminum alloy,the effect of microwave sintering and La2O3 doping on the properties of TiB2-Ni powder,and the effect of hydrostatic seawater pressure on the tribocorrosion of La2O3-TiB2-Ni coating,the tribocorrosion-resistant La2O3-TiB2-Ni protective coating was developed,and the tribocorrosion behavior and mechanism of 7075-T6 aluminum alloy,which used in marine engineering equipment commonly,and its surface La2O3-TiB2-Ni protective coating were systematically studied in-situ and non-in-situ.(1)The tribocorrosion behavior of the 7075-T6 aluminum alloy under different hydrostatic pressure is studied by using the deep-sea high-hydrostatic pressure tribocorrosion system.Electrochemical in-situ monitoring was used to analyze the electrochemical signals in each stage of tribocorrosion under different hydrostatic seawater pressure,and quantify the interaction between mechanics,chemistry,and electrochemistry in the tribocorrosion process was quantified,and the tribocorrosion mechanism in deep-sea environment was clarified.The tribocorrosion rate will increase with the increase of hydrostatic pressure,when the sea depth increases by 100 m,the tribocorrosion rate of 7075-T6 aluminum alloy increases by 0.1×10-06 mm3·N-1·m-1.During the tribocorrosion process,the selfcorrosion current density of 7075-T6 aluminum alloy increases by two orders of magnitude compared with that without wear.With the increases in hydrostatic seawater pressure,pitting corrosion sensitivity of 7075-T6 aluminum alloy was increased,and the tribocorrosion mechanism of fatigue wear and delamination wear with corrosion at 0.1 MPa will gradually change to adhesive wear and delamination wear with corrosion at high hydrostatic seawater pressure;There is an interaction between wear and corrosion during tribocorrosion,and aluminum alloy tribocorrosion is not a simple superposition of corrosion and wear.With the increase of hydrostatic pressure,the interaction effect of corrosion accelerated wear becomes the dominant factor of tribocorrosion.When the hydrostatic pressure increases from 0.1 MPa to 30 MPa,the loss of materials caused by the corrosion accelerated wear proportion increases from 7.70%to 23.13%.(2)Given the poor abrasiveness of aluminum alloy and the deficiency of TiB2Ni coating at present,a new TiB2-Ni powder doped with rare earth La2O3 was prepared by optimizing the agglomeration-microwave sintering method,and the action mechanism of rare earth La2O3 on TiB2-Ni powder was analyzed.Microwave sintering can significantly shorten the sintering time and temperature of powder,and obtain a powder with more uniform particle size and dense agglomeration than the traditional sintering process.Sintering temperature and sintering holding time are the main factors affecting the loose density and fluidity of powder.When 1.0 wt.%La2O3 is added,La2O3 inhibits the decomposition of TiB2 and the oxidation of Ni,the loose density of TiB2-Ni powder increases from 1.214 g/cm3 to 1.313 g/cm3,it can improve the loose density and fluidity of the powder.(3)La2O3-TiB2-Ni coating was deposited on the surface of 7075-T6 aluminum alloy to improve the anti-tribocorrosion performance by the atmospheric plasma spraying process.The spraying process of La2O3-TiB2-Ni coating was optimized by orthogonal test,and the mechanism of rare-earth La2O3 on TiB2-Ni coating was clarified.Finally,high-performance coatings with high hardness,high bonding strength,and excellent corrosion resistance were obtained.The material has significant phase loss and forms complex compounds such as Ni3B and Ni20Ti3B during spraying;Rare earth La2O3 doping can improve the microstructure of TiB2Ni coating,doping 1.0 wt.%rare earth La2O3 will inhibit the high-temperature decomposition and synthesis reaction between TiB2 and Ni,reduce the formation of brittle phase,and improve the hardness,bonding strength and corrosion resistance of the TiB2-Ni coating,and the self-corrosion current density of the coating decreased from 71.22 nA/cm2 to 30.24 nA/cm2.(4)Compared with TiB2-Ni coating,the tribocorrosion behavior of La2O3TiB2-Ni coating was studied,the tribocorrosion rate of La2O3-TiB2-Ni coating under different hydrostatic seawater pressure was obtained.The interaction between wear and corrosion in the tribocorrosion process was quantitatively analyzed,and the tribocorrosion mechanism of La2O3-TiB2-Ni coating in a deep-sea environment was clarified.The La2O3-TiB2-Ni coating can improve the tribocorrosion resistance of 7075-T6 aluminum alloy in deep-sea environment and it has obvious wearresistance and wear reduction effects.The tribocorrosion rate of the coating at 0.1 MPa is 1.18×10-06 mm3·N-l·m-1,compared with 7075-T6 aluminum alloy,the tribocorrosion rate at 0.1 MPa is reduced by one order of magnitude.During the tribocorrosion process,the self-corrosion current density of La2O3-TiB2-Ni coating increases by three orders of magnitude compared with that without wear.The tribocorrosion mechanism of La2O3-TiB2-Ni coating and 7075-T6 aluminum alloy in deep-sea environment is different.With the increase of hydrostatic pressure,the tribocorrosion mechanism of La2O3-TiB2-Ni coating changes from abrasive wear with corrosion at 0.1 MPa to abrasive wear with corrosion and slight adhesive wear at high hydrostatic seawater pressure.The analysis of the interaction between wear and corrosion shows that with the increase of hydrostatic pressure,when the hydrostatic pressure increases from 0.1 MPa to 30 MPa,the proportion of corrosion accelerated wear in the total material loss increased by 13.93%,mechanical wear is still the main failure factor of La2O3-TiB2-Ni coating during tribocorrosion. |
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