Research On LPES Surface Strengthening Of TC4 Titanium Alloy Gear

Lightweight structure has always been a major concern in the aviation field.The use of titanium alloy gears can greatly reduce the weight of helicopter transmission structures.However,low hardness and poor wear resistance of titanium alloy materials will lead to adhesion wear of titanium alloy gears.Liquid Plasma Electrolytic Saturation(LPES)is an effective method to improve the surface properties of titanium alloy.However,in order to strengthen the complex surfaces such as gears by LPES,key issues such as the uniformity of the electric field and the flow field must be solved.In this thesis,the complex discharge mechanism and electric field characteristics of TC4 titanium alloy gear were studied by combining theory with practice.The formation mechanism and conditions of strengthening layer were explored.A series of parameters optimization researches on the quality and performance of the strengthening layer were carried out.The purpose of the research is to provide technical support for the application of LPES surface strengthening on titanium alloy gear.The main work and achievements of this thesis are as following:1.The multi-physical fields involved in the strengthening process were analyzed,and a simulation model of the surface strengthening system was established.The electric field,flow field and temperature field in the system under different conditions were simulated.Studies have shown that reasonable design of the electrode system parameters can ensure the uniformity and stability of the electric field and flow field.The maximum temperature of the workpiece surface increases with the increase of the voltage,and the highest point of the system temperature is at the gas film between the electrodes.2.The discharge mechanism on complex surface and electric field characteristics of gears were researched.The formation mechanism and conditions of the strengthening layer on the titanium alloy gear by LPES were studied.Results indicated that the fundamental reason for the difficulty of effective discharge on the gear surface lies in the uneven electric field.During the strengthening process,the electrolyte system,electrode shape,electrode distance,and inlet flow velocity all affect the stability of the electric field and the formation of the layer.The premise of strengthening layer formation needs to meet the basic electrical parameters.Under different voltage,the surface temperature of workpiece goes through four stages,and remains relatively stable at last.According to the principle of thermodynamics,the forming conditions of strengthening layer were analyzed,and the possibility of strengthening layer formation was verified by thermodynamic calculation.Theoretical analysis shows that the diffusion mechanism of atoms in titanium alloys is interstitial diffusion and vacancy diffusion.According to the calculation results of the diffusion theory model,the relationship between atomic diffusion rate and voltage was obtained,which provides guidance for the selection of surface strengthening parameters of titanium alloy gears.3.The surface morphology,element distribution,hardness,and anti-wear behavior of the strengthening layer under different voltages and times were studied through process experiments.The results show that the strengthening layer prepared on the titanium alloy gear has a gradient element distribution,high surface hardness,and good anti-wear ability.