| This project is a part of Natural Science Foundation of Shaanxi Province?2018JM5056?.In this thesis,the performance requirements of moving parts of marine equipment are constantly upgraded.The tribological properties of Si3N4-hBN ceramic composites and TC4 titanium alloy?Ti6Al4V?sliding pairs in seawater,saltwater environments,marine atmospheric and deionized water atmospheric environments are studied,and the corrosion behavior of pure Si3N4and Si3N4-hBN ceramic composites in seawater environment is preliminarily explored.The friction and wear mechanism and self-lubrication mechanism of sliding pairs in seawater and marine atmospheric environments are discussed in detail.The effect of hBN content on the tribological properties of Si3N4-hBN ceramic composite and TC4 titanium alloy pairs is also discussed.The purpose of this study is to explore the effects seawater environment and marine atmospheric environment on the friction and wear properties of Si3N4-hBN/TC4sliding pairs.Friction and wear tests were carried out with the help of a model MMW-1 vertical universal friction and wear tester.Scanning electron microscopy?SEM?was used to observe the micro-morphology of worn and corroded surfaces.The phase composition of worn surfaces was analyzed by EDS,XRD,XPS and Raman spectroscopy.This paper mainly completes the following research work:?1?In this thesis,the effects of seawater and saltwater on the tribological properties of Si3N4-hBN/TC4 sliding pairs were studied.The antifriction mechanism of hBN content in two different environments was discussed,and the lubrication mechanism model of Si3N4-hBN/TC4 sliding pair in seawater environment was established.The results showed that the wear resistance property of silicon nitride-based ceramics and titanium alloy sliding pairs is significantly improved by adding hBN in both environments.When the content of hBN reaches 30 wt.%in seawater,the friction coefficient of sliding pair decreases from 0.67 of pure Si3N4/TC4 sliding pair to 0.028 of Si3N4-30wt.%hBN/TC4 sliding pair,and the wear rate of titanium alloy disc specimen decreases from 10-4mm3/Nm to 10-5mm3/Nm.In saltwater environment,the friction coefficient of sliding pair decreases from 0.553 of pure Si3N4/TC4sliding pair to 0.0932 of Si3N4-30 wt.%hBN/TC4 sliding pair.The wear rate of the titanium alloy disc specimen decreases from 5.11×10-4mm3/Nm to 1.27×10-4mm3/Nm.In both environments,when the content of hBN reaches 30 wt.%,the wear surface of sliding pair undergoes tribochemical reaction,resulting in the formation of lubricating oxides and hydroxides consisting of SiO2,TiO2,H3BO3and Al?OH?3.Meanwhile,there are MgCO3 and CaCO3 lubricants on the worn surface in seawater environment.Moreover,Ca2+and Mg2+cations in seawater can help the tribo-chemical reaction products aggregate to form the lubrication protective films,which make the wear surface of the sliding pair smooth,and then make the sliding pair enter the state of fluid lubrication under the lubrication of seawater.According to the formula,at the same time,it is deduced that the friction coefficient???is proportional to the shear stress???of the film between the sliding pairs,while the Al?OH?3 colloid has a smaller shear stress,so that the sliding pair has a smaller friction coefficient,which shows that the seawater environment is a good lubricating medium for the Si3N4-30 wt.%hBN/TC4 sliding pair.?2?In this thesis,the effects of marine atmospheric environment and deionized water atmospheric environment on the tribological properties of Si3N4-hBN/TC4 sliding pairs were studied.The antifriction mechanism of hBN content in two different environments was discussed,and the lubrication mechanism model of Si3N4-hBN/TC4 sliding pair in wet environment was established.The results show that the wear resistance property of sliding pairs are improved significantly by adding hBN in both environments.The friction coefficient of sliding pair decreases from 0.583 of pure Si3N4/TC4 sliding pair to 0.302 of Si3N4-20 wt.%hBN/TC4 sliding pair in marine atmospheric environment,and the wear rate of titanium alloy disc specimen decreases from2.78×10-4mm3/Nm to 1.46×10-4mm3/Nm.In deionized water atmosphere,the friction coefficient of sliding pair decreases from 0.613 of pure Si3N4/TC4sliding pair to 0.337 of Si3N4-30 wt.%hBN/TC4 sliding pair,and the wear rate of titanium alloy disc specimen decreases from 2.70×10-4mm3/Nm to 1.30×10-4mm3/Nm.In both environments,oxides and hydroxides consisting of SiO2,TiO2,H3BO3 and Al?OH?3 with lubricating effect are formed during the friction process of the sliding pair.Meanwhile,there is Mg?OH?2 lubricant on the worn surface in the marine atmospheric environment.Ca2+and Mg2+cations in the marine atmosphere helps the tribo-chemical reaction products aggregate to form the solid lubricating film,which protects the wear surface of the sliding pair and keeps the wear surface smooth.According to the formula,at the same time,it is deduced that the friction coefficient???is proportional to the shear stress???of the film between the sliding pairs,while the Al?OH?3 colloid has a smaller shear stress,so that the sliding pair has a smaller friction coefficient.This shows that the marine atmospheric environment is a good lubricant for Si3N4-20 wt.%hBN/TC4 sliding pair.?3?The effect of seawater environment on the corrosion behavior of pure Si3N4 and Si3N4-hBN composite ceramics was also studied in this thesis.The effects of corrosion time and hBN content on the corrosion behavior of specimens were mainly discussed.By comparing with the corrosion resistance of metals and analyzing the corrosion products,the following conclusions were drawn:When the content of hBN is fixed,the corrosion rate of specimens decreases with the passage of corrosion time.When the corrosion time is fixed,with the increase of hBN content,the corrosion rate of the specimens also shows a downward trend.Especially when the corrosion time is 12 days,the corrosion rate decreases from 0.0109g/?m2?h?of pure Si3N4 to 0.0037g/?m2?h?of Si3N4-30 wt.%hBN composite ceramics,which almost reaches the very corrosion resistance grade of metal.Thus,it shows excellent seawater corrosion resistance.This is due to the oxidation reaction of the corrosion products of the specimens,the SiO2 and H3BO3 formed on the surface of the specimens prevents them from being further eroded by seawater.The research in this thesis shows that Si3N4-hBN composite ceramics have good tribological properties in seawater environment and marine atmosphere environment,and Si3N4-hBN composite ceramics exhibit excellent corrosion resistance in seawater environment.This not only enriches the tribological theory of ceramic materials in marine environment,but also provides theoretical support for the research and application of key sliding pairs in marine environment. |
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