Investigation On The Tribological Properties Of The WC-Al₂O₃ Composites Under Different Working Conditions

Cemented carbides has very important application value in coating,anti-wear parts and other aspects.In particular,traditional cemented carbide?WC-Co?plays a key role in the application and research fields.However,cobalt is a rare and expensive strategic resource.Therefore,it is necessary to develop novel cemented carbide.In recent years,my research team has done a lot of work on the preparation and mechanical properties of the WC-Al₂O₃ composite.On this basis,further investigation on the tribology performances of the new material is necessary to provide reference for the application,which has important academic value and application significance.In this dissertation,the friction and wear behaviors of WC-Al₂O₃ composite under different environments and working conditions were investigated using the ball-on-disc sliding friction and wear test method.The home-made WC-Al₂O₃ composites were used as the research object,and the industrial traditional cemented carbide YG8 was regarded as comparative objective.The wear mechanisms were analyzed by characterizing the wear surface morphology,the debris morphology and the related chemical composition.The main research results of this dissertation include:1?The friction and wear behavior of the WC-Al₂O₃ composite?WA15?under different working conditions at room temperature was systematically studied.The results show that:?1?The friction and wear behaviors,and the wear mechanisms under different loads are significantly different.According to the Hertz contact model,the contact stresses corresponding to different loads are calculated.The applicable stress conditions of the material are defined based on the wear transition load.When WA15paired with YG6 cemented carbide,the friction coefficient increased with the load,and the wear rate firstly remained steady and then increased sharply.Especially between30N and 40N,the material can occur wear transition from slight wear to severe wear.The wear mechanism before and after the wear transition is different,and the morphology of wear debris is different.In the mild wear stage,the wear rate is very low and hold steady.The wear mechanism is mainly micro-cutting and micro-cracking.The wear debris are agglomerate.In the severe wear stage,the wear rate increases sharply and increases significantly with the load.The wear mechanism is grain fragmentation and spalling.The wear debris is flake.?2?The effects of counter materials on friction and wear of WA15 composites are different.This provides a reference for the selection of working parameters of new materials under different working conditions.The friction coefficient of WA15/Si₃N₄ was significantly greater than WA15/YG6,and the friction curve fluctuated more strongly.However,in WA15/Si₃N₄ system,the wear rate of WA15 decreases with the increase of load,and the wear rate under the maximum test load is less than that when paired with YG6.This is because the tribological reaction of Si₃N₄ in the sliding process weakens the damage of WA15 material.?3?Under the same condition,the difference of the wear behaviors of the WA15 composite and traditional cemented carbide was compared,which provides a basis for the application of new material to replace YG8 in the application of wear-resist parts.Through comparative study,the traditional cemented carbide and the WA15 composite have the same strong load-time dependence.However,the WA15 composites have higher load caused severe wear and better wear resistance.2?Based on the above findings,the friction and wear behaviors of WC-Al₂O₃composites with different grain sizes under the load of 80N were investigated.The results showed that microstructure refinement can significantly improve the tribological properties of WC-Al₂O₃ composites.The friction coefficient,the fluctuation and the wear rate of the materials were significantly reduced after microstructure refinement.The vibration and noise in the test are also reduced obviously.The wear mechanism changes from grain fragmentation and spalling to micro-cutting,which makes the wear loss extremely slight.The main reason for the improvement of tribology performance is the enhance of fracture toughness,hardness and surface quality after microstructure refinement.Increasing the load to 120N,the WC-Al₂O₃ composite after microstructure refinement has not suffered severe wear.This indicates that microstructure refinement plays an obvious role in improving the load that caused severe wear,and the WC-Al₂O₃composite after the microstructure refinement can bear a greater load.3?The friction and wear behaviors of WC-Al₂O₃ composites?WA15?were studied in liquid medium and high temperature environment,respectively.The results show that:?1?In the liquid medium,WC-Al₂O₃ composite did not show severe wear similar to that under the condition of dry friction,indicating that the wear transition load increased.In addition,compared with the dry friction and wear test at room temperature,the friction coefficient and wear rate of the WC-Al₂O₃ composite in water and oil(C₁₆H₃₄)are greatly reduced.This is because the lubrication film formed between the interfaces plays a pressure and lubrication role.The effects of load and velocity on friction and wear behaviors are different in liquid medium.The effect of load on friction coefficient is not obvious,whereas the wear rate increases with the load increasing.However,the friction coefficient and wear rate can be reduced by increasing speed.?2?At high temperature,Nickel?Ni?plays an obvious role in improving the high temperature anti-oxidation wear property of WC-Al₂O₃ composite.In view of the serious oxidation wear of WC-Al₂O₃ composite at high temperature,Ni doped WC-Al₂O₃ composite was prepared.The new formulation and sintering process were obtained,which reduced the sintering temperature of WC-Al₂O₃ composite material under the premise of maintaining the high mechanical properties.The addition of Ni inhibited the oxidation behavior of WC-Al₂O₃ composite at high temperature,and improved the anti-oxidation wear property of WC-Al₂O₃ composite.This dissertation is the first to systematically study the tribology performances of the WC-Al₂O₃ composite.The influence of the test parameters,material microstructure and the external environment on friction and wear behavior is illustrated.The wear mechanisms of the WC-Al₂O₃ composite are discussed.This paper provides a variety of ways to improve the friction and wear properties of the WC-Al₂O₃ composite,and provides an basis for subsequent research and application.