Study On Tribological Properties Of Ti Al Matrix Self-lubricating Composites Containing Ag And ZnO

The solid lubricant has more obvious advantages in some extreme conditions such as high temperature and high pressure,if compared with the traditional liquid lubricant.However,it is difficult to meet the requirements of the tribological performance for a single solid lubricant in a wide temperature range or some extreme conditions.Therefore,it is necessary to use two or more solid lubricants to improve the tribological properties of self-lubricating materials.In this paper,by adding Ag and ZnO into TiAl matrix,a new type TiAl matrix self-lubricating composite was fabricated successfully by SPS.The tribological properties of the composites under different temperature,sliding speed,load and friction pair were studied by changing the working condition.The friction and wear mechanism of TiAl matrix selflubricating composite material and its self lubricating mechanism were discussed.In the process of dry sliding friction,the samples exhibit different tribological behaviors under different working conditions.At room temperature to 800℃,the friction coefficient and wear rate of TiAl-3.5Ag-6.5ZnO(T1),TiAl-5.0Ag-5.0ZnO(T2)and TiAl-6.5Ag-3.5ZnO(T3)are significantly different in different temperature ranges,and the tribological properties of T2 is relatively better.The friction coefficient of T2 increases first and then decreases with the increase of sliding velocity from 0.2 to 0.8m/s,and the lowest value is obtained at 0.6m/s,which is 0.18.Under the condition of 5-20 N load,the friction coefficient and wear rate of T2 show a trend of decreasing first and then increasing with the increase of applied load,and the lowest value is obtained at 15 N,which is 0.21.The tribological behavior of T2 is quite different if different friction pairs are used.When the hardness of the grinding ball is more close to the hardness of the grinding material T2,T2 has better tribological properties.TiAl based self-lubricating composites exhibit excellent tribological properties due to the synergistic lubrication effect of solid lubricant Ag and ZnO,which improves the self-lubricating properties of the composites.The wear surface of the material with good tribological properties is covered with a friction layer with different integrity.When the thickness of the friction layer is thicker,the wear surface of the composite is smoother and the tribological properties is better.The friction heat andplastic deformation are the main reasons for the formation of friction layer.The friction layer can be divided into lubricating layer and grain refining layer.The main components of the lubrication layer include titanium aluminum oxide and solid lubricant Ag and ZnO,which can achieve good friction reduction and wear resistance,and the grain refinement layer provides support for the lubrication layer.The formation process of the friction layer is divided into three stages: the first stage is the work hardening;the second stage is grain refinement;the third stage is the formation of the friction layer.In this paper,the formation and the mechanism of the friction layer are analyzed,and the theoretical basis of the solid self-lubricating composites is discussed.