Study On The Lubricating Mechanisms And The Analysis Of Working Longevity Of MoO₃ Tabular Crystal Enhanced TiAl Matrix Composites

In order to satisfy the antifriction wear-resisting requirements under extreme conditions such as high temperature,high speed and heavy engineering machinery,solid self-lubricating materials attract more and more attention.However,excellent self-lubricating materials remain to be discovered.MoO₃ tabular crystal,which has special multilayer structure,is added into TiAl based alloy to fabricate TiAl matrixs self-lubricating composite?TMSC?which has good tribological properties.The influences of MoO₃ tabular crystal on tribological performance of TMSC under different conditions are studied.The antifriction and antiwear mechanisms of MoO₃tabular crystal in TMSC are analyzed.The working longevity of TMSC is predicted and the predication accuracy is verified.The results are as follows:During the dry sliding process,the influences of MoO₃ tabular crystal on tribological performance of TiAl matrix composites under different conditions are different,which are studied under different temperature,loads,friction pairs and sliding time by comparing to TiAl based alloy.MoO₃ tabular crystal can promote tribological performance of TMSC over a wide temperature range of 25-600°C,especially at 400°C.The structure of MoO₃ tabular crystal is destroyed when the temperature is over 400°C,leading to that the MoO₃ tabular crystal loses the functions.MoO₃ tabular crystal can promote tribological performance of TMSC with the increase of load.MoO₃ tabular crystal can promote tribological performance of TMSC against different friction pairs.The whole sliding progress can be divided into three stage with different sliding time.At preliminary sliding stage,MoO₃ tabular crystal plays better roles with the increase of sliding time,hence the wear rate and friction coefficient of TMSC decrease gradually.At stable sliding stage,MoO₃ tabular crystal plays active roles in making the tribological performance of TMSC keep good steadily.The last stage is sharply increasing stage,and MoO₃ tabular crystal loses the functions when the sliding time is over 300 min.During the dry sliding process,the friction surface will be formed an uniform and dense refined structure named friction layer,which can improve tribological performance of materials.MoO₃ tabular crystal can occur interfacial slipping and stripping due to the special mutilayer structure,which has weak binding force between layer and layer.The interfacial slipping can relieve the stress concentration to prevent the crack producing and propagation,which can protect the friction layer from being destroyed.The interfacial stripping can make MoO₃ tabular crystal be distributed more equally,which can enhance the grain refinement,promoting the formation of friction layer.When the stress is higher,MoO₃ tabular crystal occurs interfacial slip and stripping more thoroughly.It means that MoO₃ tabular crystal can play better roles in protecting friction layer from being destroyed and promoting the formation of friction layer.Meanwhile,the crack is produced for the higher stress,and MoO₃ tabular crystal prevents the crack propagation.Moreover,MoO₃ tabular crystal loses the functions when the stress is too high to relieve.Predication formula is constructed on account of the Piecewise cubic Hermite interpolation to predict the working longevity of TMSC.The predication curve figure matches with the changing trend of the experimental results of wear rates.The wear rate decreases from the beginning to 60 min,and then keeps stable for 240 min at low value.However,the wear rate of TMSC gradually increases from 300 min to the end of 340 min.It means that the predication is correct and the working longevity is predicted as 300 min due to that MoO₃ tabular crystal loses the functions after sliding300 min.The predication accuracies of the Piecewise cubic Hermite interpolation are proved to be more superior,which are all more than 90%,if compared to those of Newton interpolation.Moreover,the predication accuracy shows similar trend like wear rate.It means that worn surface and friction layer becoming smoother and completer with the increase of sliding time can offer better feedback.This thesis offers some experiences for studying the application and lubrication mechanism of MoO₃ tabular crystal.The interpolation function is proved to be an effective method to analyze working longevity which is hard to be tested.It can guide the practical engineering application.