Failure Behavior Of Silicon Nitride Ceramic Ball Crushing And Thermal Shock

With the development of ceramic ball bearings,ceramic ball bearings are widely used in different fields in the current bearing market because of their advantages of low density,excellent friction performance,chemical corrosion resistance and high strength.In the harsh working environment of high temperature,temperature field and high impact,the probability of crushing failure and thermal shock failure of silicon nitride ceramic ball in bearing will be greatly increased.Based on the experiment and Ansys Workbench finite element analysis,the mechanism analysis of the crushing failure process and thermal shock failure of silicon nitride ceramic ball is completed.According to the failure behavior of ceramic ball in the process of using,this paper uses two-spherical pressure method to change the compression load of silicon nitride ceramic ball with different diameters,and observe the surface crack morphology under stereomicroscope.It is observed that there will be two kinds of cracks in ceramic ball surface under compression load.Aiming at the thermal shock resistance of silicon nitride ceramic ball,this paper uses Ansys Workbench to simulate the cooling process of ceramic ball in different cooling media.It is found that the main reason for the failure of ceramic ball thermal shock is that the cooling rate of ceramic ball surface is too fast and the local tensile stress is too large during the thermal shock process,which leads to the cracking of ceramic ball surface.According to the convection heat transfer coefficient of air and water,the optimization function of surface convection heat transfer coefficient and time of two kinds of ceramic balls in the process of water entry is designed,and the maximum cooling rate of ceramic balls with different diameters in the cooling process is obtained.According to the change of temperature field during the cooling process of silicon nitride ceramic ball,the thermal shock experiment of silicon nitride ceramic ball was carried out,and the failure type of ceramic ball surface was observed by body-view microscope,and the experimental phenomenon corresponding to the simulation results was obtained.The conclusion was reached that the failure form of the smaller diameter ceramic ball surface was spalling at 750 ℃,and the larger diameter ceramic ball surface would appear crack.Finally,the process of evaluating the thermal shock resistance of ceramic ball is designed.