Study On High Temperature Self Lubrication Characteristics Of Automotive Engine TiAl Based Alloy Exhaust Valve

With the progress of engine technology,the quality requirements of valve train are improved,and lightweight design has become an important direction of engine design.Exhaust valve is one of the key parts of engine valve train,and it works in high temperature and heavy load environment,the working condition is very bad,the wear condition is very serious,so the preparation of a light,high temperature strength,high temperature self-lubricating exhaust valve has a broad application prospect.Ti Al based alloy is an ideal exhaust valve material because of its low density,high specific strength and excellent mechanical properties at high temperature.In this paper,the mechanical properties of ti-45al-8nb-0.3y alloy were improved by adding appropriate amount of tic and Ti B2 particles,and then Ca F2 was added to make the alloy have high temperature self-lubricating properties.The exhaust valve material with light weight,excellent mechanical properties and high temperature self-lubricating properties was prepared.The composition of Ti Al based alloy was designed by orthogonal experimental design.The Ti Al based alloy with different composition was prepared by vacuum hot pressing sintering technology.The bending strength,fracture toughness,density,hardness,friction coefficient and wear rate were tested.The results show that with the increase of tic and Ti B2,the mechanical and physical properties of Ti Al Based Self-lubricating Materials first increase and then decrease.When the mass fraction of Ti C,Ti B2 and Ca F2 is 6%,3.5% and 9%,respectively,the comprehensive performance of the alloy is the best.The friction and wear tests of Ti Al based alloy with the optimal composition under different temperatures and different loads were carried out.The high temperature self lubrication mechanism of Ti Al based alloy was explored,and the better working temperature and working load range of Ti Al based alloy were determined,which provided a theoretical basis for the practical application of Ti Al Based alloy exhaust valve.The preliminary structure design of the exhaust valve is carried out.The three-dimensional model of the exhaust valve is established by using Solid Works software.After establishing the stress model of the exhaust valve and determining the thermal boundary conditions of the exhaust valve,the thermal mechanical coupling simulation analysis of the exhaust valve made of Ti Al based alloy and 21-4N valve steel is carried out by using workbench software.The structure of the exhaust valve is improved and the exhaust valve is improved The distribution of stress is analyzed.The thermal mechanical coupling simulation analysis of the exhaust valve die was carried out by DEFORM software,and the exhaust valve structure was further improved to improve the stress of the die and exhaust valve,and prolong the service life of the exhaust valve and the die.The dynamic simulation analysis of valve train is carried out by ADAMS software.The simulation results show that the use of Ti Al based self-lubricating alloy can effectively reduce the contact force between cam tappets,so as to reduce the wear of cam tappet,and the movement of exhaust valve is in good condition without valve bounce and valve flying off.