Research On The Processing Of Electrical Discharge Surface Strengthening On TC4 Alloy With Different Medium

With the rapid development of science and technology and the manufacture of precision products,the demand of the comprehensive properties of TC4 alloy becoming more and more crucial. Titanium alloy has excellent advantage, such as light mass, corrosion resistance, high strength, non-magnetism and so on, but the poor wear resistance, the low hardness and deformation easily make the application in aerospace and automobile industry and other fields restricted. In order to resolve the problem, the surface treatment technology( cementation, coating, surface heat treatment and so forth) improve the above disadvantage to some extend. The surface modification by EDM can improve on surface organization characteristic and not to change the mechanical properties of TC4 alloy. So this technology becomes the hot topic in the filed of surface engineering. Research on the processing of electrical discharge surface modification on TC4 alloy in in kerosene medium, gas medium and mixed powder dry medium(gas、liquid and B4C).The temperature field and stress field of electrical discharge surface strengthening are simulated by ABAQUS finite element software. The influence of different process in EDM surface strengthening on temperature field and stress field is studied. The result of temperature field indicates that the temperature increases with the increase of machining time and the electrical discharge peak current at the same position, The width and depth of molten pool increase with the peak current, the influence on width is remarkable. The center temperature decreases with the increase of pulse duration, and pulse duration has little effect on pulse duration. The analysis of stress field indicates that the stress of strengthening layer increases little with the peak current and pulse duration after discharge. The residual stress of strengthened layer is minimum after discharge and cooling when peak current 6.6A and pulse duration 60μs.The electrical discharge surface modification experiment is done on TC4 alloy in kerosene medium, gas medium and mixed powder dry medium. The influence of peak current, pulse duration and pulse interval on the microstructure morphology and micro-hardness of the strengthened layer is studied by the single variable method. The microstructure morphology of the strengthened layer is observed. The process parameters are optimized in different medium. The strength ratio time and wear resistance of strengthened layer are studied. The experiment shows that the strengthened layers vary considerably in different medium, The strengthened layer grows well and micro-hardness is about 900 HV. But it is nonuniform and low micro-hardness and lower surface finish, it takes longer time than the other experiments at the same depth. The comprehensive properties of strengthened layer is best in mixed powder dry medium by the same process, the micro-hardness of the strengthened layer is 2.5 times than that of TC4 alloy, the wear resistance of the strengthened layer is better than it in kerosene and gas medium.In the mixed powder dry medium, further research about the process of composite strengthening is made on TC4 alloy. In order to obtain the better strengthened layer, the composite current and different electrode material are studied. The results shows that high current can make the strengthened layer thicker and low current can get better microstructure and decrease the microrack. The strengthened layer is better by the current 8.2A+6.6A, the wear resistance are 3 times than the matrix material.Under the same process parameters, the strengthened layer gained by graphite+copper is better than copper+graphite, and the both are much better than single electrode material.