Electron beam improves corrosion resistance of titanium alloys
Titanium alloys are widely used because of a series of excellent properties. However, titanium alloys have high friction coefficient, are very sensitive to adhesive wear and fretting wear, have poor wear resistance, are easy to ignite under high temperature and high speed friction, and have relatively poor resistance to high temperature oxidation. The shortcomings seriously affect the safety and reliability of its structure and greatly limit its application. Therefore, improving the surface properties of titanium alloys such as wear resistance, high temperature oxidation resistance and corrosion resistance is an urgent problem to be solved. In addition to improving the composition and preparation process of alloys, surface modification of titanium alloys is currently the most effective method.
In recent years, electron beam surface treatment technology has developed rapidly. When the electron beam with high energy density acts on the surface of the material, the surface of the material has physical, chemical or mechanical properties that are difficult to achieve by conventional methods, and significantly improves the wear resistance and corrosion resistance of the material surface. and high temperature oxidation resistance. MCC Eastern Engineering Technology Co., Ltd. used pulsed high-current and low-energy electron beams for surface treatment of titanium alloys, and achieved good results.
The material used in the experiment is TA15 titanium alloy (Ti-6.5Al-2Zr-1Mo-1V). After the surface of the sample is polished, the surface is modified by a high-current pulsed electron beam. The electron beam acceleration voltage is 27kV, the target distance is 80mm, and the pulse The number of times is 10, and the pulse interval is 45s.
The hardness test of the obtained samples shows that with the increase of depth, the hardness value first decreases and then increases, and finally tends to a constant value. This special oscillating curve distribution can be explained as follows: under the rapid irradiation of pulsed high energy, thermal shock waves will germinate in the energy absorbing layer of the material, and will be reflected back when encountering the interface. Multiple irradiations cause the stress waves to interfere with each other and superimpose each other, presenting a complex stress distribution state, resulting in a special distribution form of cross-sectional microhardness.
The wear volume of the samples after electron beam treatment is 3 times higher than that of the original samples, indicating that the wear resistance of TA15 titanium alloy after electron beam treatment is improved. It is deposited in a small area of the subsurface layer of the material, so that the material is rapidly heated up to the phase transition temperature or above the melting temperature, and then cooled by the matrix to achieve ultra-high-speed cooling (about 109K/s), so that the surface of the material has a quenching effect and plays a solid solution. (2) The rapid solidification process of the electron beam will refine the grains of the surface layer of the material, thereby improving the wear resistance of the material; (3) When the electron beam pulse acts on the surface of the material, The temperature begins to increase rapidly, resulting in inward propagating compressive thermal stress waves due to the restrained rapid outward thermal expansion of the material surface. Residual stress is distributed as compressive stress, which is beneficial to improve wear resistance.
The corrosion performance test showed that the corrosion potential of the original sample increased from -258.3mV to -107.5mV after electron beam surface treatment, and the polarization resistance increased from 0.796k/cm2 to 2.424k/cm2 of the original sample. At the same time, the self-corrosion current was higher than that of the original sample. decreased significantly. This shows that the corrosion resistance of the sample is significantly improved. The main reasons for the improvement of the corrosion performance are: (1) the high temperature caused by the strong current pulsed electron beam irradiation on the surface of the sample can vaporize or desolvate the impurities adsorbed or adhered on the surface of the material, which plays a cleaning role; (2) the material The surface melts rapidly, and then solidifies at the same high speed. This process inhibits equilibrium crystallization, resulting in a dense non-equilibrium structure with uniform composition, which also inhibits the occurrence of self-corrosion to a certain extent; (3) The surface layer of the material The rapid cooling of the surface refines the surface grains, which leads to the reduction of the ratio of the area of the cathode to the anode and the reduction of the corrosion rate.
