Numerical Simulation For Surface Modification Of Titanium By High Current Pulsed Electron Beam

Titanium alloys have low density, high melting point, high strength, and other outstanding performances, which made them get people’s more attentions. So titanium alloys are widely used in various industries, such as aerospace, biomedical. However, titanium alloys are limited in certain applications due to their poor wear resistance, extraction difficulty, easily oxidation in the high temperature and some other disadvantages. So it is very necessary to develop new methods to reduce the production costs and improve their overall performances. The high current pulsed electron beam (HCPEB) can generate special effects to the material surface, which becomes an effective surface modification technology. There is metastable phase in the material surface treated by the HCPEB. And after the processing of the HCPEB, the surface hardness and wear properties are improved. We analyzed the effect and mechanism of solid phase transformation induced by the HCPEB using numerical simulation method in this paper. In order to optimize the process parameters of the titanium alloy surface modification, improve the surface properties and explore new application in titanium industrial.In order to simulate the beta-CEZ titanium alloy’s dynamic temperature field and stress field caused by the HCPEB, a two-dimensional axisymmetric model was built using the finite difference and finite-element method in this paper. The selected material parameters are dependent on the temperature, and the solid-liquid phase change latent heat is also considered. We obtain the simulation results as below:1^There are temperature field results of the beat-Cez titanium alloy irradiated by the HCPEB. The maximum melting depth is1.0μm at irradiation energy of3J/cm2under a single pulse. The heating and cooling rate of surface changes with time, and the maximum is up to109K/s. The cooling process shows a apparent melt platform due to the relatively lower temperature gradient. At a point time the temperature gradient is different with position. According to the principle of thermal expansion and contraction, the temperature gradient can cause deformation and generate stress in the surface layer. By comparing the thickness of martensitic transformation layer with the temperature effect depth, we can conclude that the temperature is not the direct cause for the martensitic transformation. 2、The stress field is simulated by the finite-element method. The results show that there is quasi-static thermal stress in the surface. Within a surface depth down to2.4μm there exists compressive stress. The maximum compressive stress is about2.60GPa. The tensile stress reaches the depth of12μm, and the value is above100MPa. Since the maximum stress triggering the martensite transformation would reach2.40GPa according to the literature, which is comparable to the maximum quasi-static thermal stress of2.60GPa. Such a martensite transformation should be induced by a chock stress originated from the quasi-static thermal stress. The corresponding stress attenuation coefficient is about173mm-1.