Study On Preparation And Structure Properties Of Ti Doped Diamond-like Carbon Film On Aluminum Alloy For Piston

Aluminum alloy has excellent properties of light weight,high specific strength and easy forming,which is an ideal material for engine pistons.However,low hardness,poor wear resistance and corrosion resistance of the aluminum alloy will produce great friction work and increase energy consumption in the continuously reciprocating process of sliding parts such as the skirt and the cylinder in the all-aluminum piston.In severe cases,the piston will fail.The diamond-like carbon（DLC）film with high hardness,low friction coefficient,excellent wear resistance and corrosion resistance,is used for the surface treatment of the aluminum alloy piston,which can effectively improve its comprehensive performance.In this paper,based on element doping and multilayer film technology,the Ti-DLC multi-layer composite film with Ti transition layer,Ti-DLC layer and Ti buffer layer,was prepared on the aluminum alloy surface by filter cathode vacuum arc（FCVA）deposition equipment.In addition,the effects of C2H2 gas flow and Ti transition layer thickness on the microstructure and properties of Ti-DLC film were systematically studied.On this basis,the ultra-thick Ti-DLC film was deposited on the aluminum alloy surface,and its performance was evaluated.The main work and conclusions are as follows:（1）The results of the study on the influence of C₂H₂ gas flow on the performance of Ti-DLC film show that the Ti-DLC multilayer composite film has a typical DLC structure,and the morphology of surface is“hilly”with macroparticle and microvoid defect.As the C₂H₂ gas flow increases,the Ti element content in the Ti-DLC film decreases gradually,and the sp³-C contentincreases first and then decreases,when the C₂H₂ gas flow is 80 sccm,the sp³-C content is the highest.In addition,when the C₂H₂gas flow is less than 80 sccm,the hardness and adhesion of Ti-DLC film are gradually increased,and the friction coefficient is more than 0.5.However,when the gas flow is greater than or equal to 80 sccm,the tribological properties of the Ti-DLC film are greatly improved,and the friction coefficient is about 0.12.Selecting a suitable C₂H₂gas flow is beneficial to improve mechanical properties of the Ti-DLC film.（2）The results of the study on the influence of Ti transition layer thickness on the performance of the Ti-DLC film show that the Ti transition layer thickness has little effect on the composition and structure of the Ti-DLC film,and the sp³-C content remains basically unchanged.However,the addition of the Ti transition layer can improve the interfacial transition between the Ti-DLC film and the aluminum alloy substrate,which is beneficial to enhance the adhesion performance and improve the stability of tribological property.In addition,with the increase of the Ti transition layer thickness,the residual stress of the Ti-DLC film decreases first and then increases,while the adhesion is opposite to the change law.Selecting a suitable Ti transition layer thickness is beneficial to improve the adhesion performance of the Ti-DLC film.（3）The results of the study on preparation and performance evaluation of ultra-thick Ti-DLC film show that based on the previous experimental investigation,a Ti-DLC multilayer composite film with the aluminum alloy/Ti transition layer/Ti-DLC layer/Ti buffer layer/Ti-DLC layer/Ti buffer layer/Ti-DLC layer was successfully deposited on the aluminum alloy,the thickness is 17²0μm.The ultra-thick Ti-DLC film has a nanohardness of 18 GPa and an elastic modulus of 153 GPa,and has good toughness and elastic recovery.At 300°C,the ultra-thick Ti-DLC film has excellent tribological properties with a friction coefficient of 0.1185 and a wear rate of 2.5×10^-5mm³/（N?m）.In addition,the ultra-thick Ti-DLC film has a certain thermal insulation performance,and the thermal conductivity of the aluminum alloy deposited with the ultra-thick Ti-DLC film is reduced by about 25 W/m*K compared with the aluminum alloy substrate.