| There are many outstanding advantages on titanium alloy as an emerging structural material compared with traditional metal materials.In recent years,there have been relevant researches on the application of titanium alloys to internal combustion engine pistons.In view of the key problem of poor wear resistance of the TC4 titanium alloy,combined with the specific movement conditions of the piston,different methods are applied to the surface of the TC4 titanium alloy in different parts of the piston.The tribological properties of TC4 titanium alloy treated in different ways are analysed.The details are as follows:(1)First,the TC4 piston model is established and the temperature field of the piston is analyzed under the ANSYS WORKBENCH simulation software.The results show that the highest temperature of the piston appears on the top surface and the fire bank position.At the same time,the force situation and contact state during the movement are analyzed to preliminarily determine the type of wear.According to the temperature field simulation and static analysis results,a reasonable piston surface treatment process is designed.(2)In view of the high temperature area on the top of the piston,a high temperature boronizing process is used to increase the surface hardness of this area.The effect of different heat preservation time at 1000? on the thickness of boronized layer is studied.SEM observation results show that micro-projection particles are formed on the surface of the substrate after the boronizing treatment.With the increase of boronizing time,the micro-projections become denser,the thickness of the infiltrated layer continues to increase,and the hardness gradually increases,too.A ball-disk friction testing machine s used to study the tribological properties of boronized surfaces under different loads and sliding speeds.Under dry friction conditions,the friction coefficient of the boronized surface is higher than that of the non-boronized surface,but the wear resistance of the boronized surface is better.When used for oil lubrication,the surface with the thinnest permeable layer is taken as an example.Its friction coefficient is about 50%of that of the matrix.There are no obvious signs of wear on the surface,which shows an excellent anti-wear performance(3)Aiming at the problem of difficult storage of lubricating oil at the top and bottom dead centers of the piston,micro-arc oxidation is used to prepare a porous wear-resistant ceramic layer to improve the storage performance of the lubricant and wear resistance.As the micro-arc oxidation time increases from 5 min to 15 min,thicker the micro-arc oxidation film becomes and higher the hardness gets from 253HV0.5 of the substrate to 2028HV0.5(micro-arc oxidation for 15min),but the surface pore diameter and film roughness raise,too.The oxide film treated for 5 min has the lowest friction coefficient,but it is easy to be worn through With the extension of the micro-arc oxidation time,the anti-wear performance of the oxide film is improved.Under starving lubrication,the micro-arc surface wear scar was the deepest in sample of micro-arc oxidation for 5 minutes,and the shallowest in 15 minutes.Under the lubrication of PAO10 oil,the wear on the surface treated for 5 minutes is lighter than that of PAO4 oil lubrication.PAO10 oil has better lubrication performance(4)For the problem of uneven wear in the middle of the cylinder during the movement,graphene-resin solid lubricating coating is used for protection.Studies have shown that the proper amount of graphene will improve the abrasion resistance of the coating,but the friction coefficient increases under too much addition.The best anti-friction and wear resistance is found on the 0.8%graphene coating surface.Further,reducers MoDTC,BDDP and lubricant PAO10 are applied to the boundary lubrication of the coating,the coatings all behaves good wear resistance.Compared to the addition of friction reducers MoDTC,BDDP,lubricant PAO10 oil performs best under boundary lubrication conditions. |
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