Titanium alloy super corrosion resistance is how to make it?

- Apr 23, 2018-

Titanium alloy super corrosion resistance is how to make it?

Titanium alloys are widely used due to their excellent properties. However, titanium alloys have a high friction coefficient and are very sensitive to adhesive wear and fretting wear. They have poor wear resistance, high-temperature high-speed friction and easy ignition, and relatively poor resistance to high temperature oxidation. Disadvantages seriously affect the safety and reliability of its structure, greatly limiting its application. Therefore, improving the surface properties such as wear resistance, high temperature oxidation and corrosion resistance of titanium alloys is an urgent problem to be solved. In addition to improving the composition of the alloy and the preparation process, the surface modification of the titanium alloy is currently the most effective method.

In recent years, electron beam surface treatment technology has developed rapidly. When an electron beam with a high energy density is applied to a material surface, the material surface has physical chemical or mechanical properties that are difficult to achieve by conventional methods, and the wear resistance and corrosion resistance of the material surface are significantly improved. And high temperature oxidation resistance. A domestic engineering and technology company used pulsed high-current low-energy electron beams to surface treat titanium alloys and achieved good results.

The material used for the experiment was TA15 titanium alloy (Ti-6.5Al-2Zr-1Mo-1V). After the surface of the sample was polished, the surface was modified with a high-current pulsed electron beam. The electron beam acceleration voltage was 27kV, the target distance was 80mm, and the pulse was The number of times is 10 and the interval between pulses is 45s.

The hardness test of the obtained sample shows that as the depth increases, the hardness value decreases first, then rises, and finally tends to a fixed value. This special oscillatory curve distribution can be interpreted as: Under the pulse high-energy fast irradiation, the material will absorb the heat shock wave in the energy absorption layer and will reflect back at the interface. Multiple exposures cause the stress waves to interfere with each other, present a complex distribution of stress, and make the microhardness of the section present a special distribution.

After e-beam treatment, the wear volume of the sample after the electron beam treatment is increased by 3 times compared with the original sample, which indicates that the wear resistance of the TA15 titanium alloy after electron beam treatment can be improved. The reason may be the following three aspects:

(1) The high energy of the electron beam is instantaneously deposited in a very small area of the material's sub surface layer, so that the material is quickly heated to a phase transition temperature or melting temperature, and then the substrate is thermally conducted to achieve ultra-high speed cooling (about 109 K/s), making the material surface Quenching effect occurs and acts as a solid solution strengthening, so the wear resistance of the surface increases;

(2) The rapid solidification process of the electron beam will refine the grain 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 rise rapidly, and the inwardly propagating compressive thermal stress wave is generated due to the constrained outward rapid thermal expansion of the material surface. The distribution of residual stress into compressive stress is beneficial for improving wear resistance.

Corrosion test showed that the corrosion potential increased from -258.3mV to -107.5mV in the original sample and the polarization resistance increased from 0.796k/cm2 to 2.424k/cm2 in the original sample, and the self-corrosion current was higher than that in the original sample. The drop is obvious. This shows that the corrosion resistance of the sample is significantly improved. The main reasons for the improvement of corrosion performance are:

(1) The high temperature caused by the intense pulsed electron beam irradiation on the surface of the sample can cause the adsorbed or adhered impurities on the surface of the material to vaporize or desolvate and play a role in cleaning;

(2) The surface of the material is rapidly melted and then solidified at the same high speed. This process inhibits the equilibrium crystallization and produces a dense, non-equilibrium tissue structure with uniform composition, which also suppresses the occurrence of self-corrosion to some extent.

(3) The rapid cooling of the surface layer of the material will refine the surface grains, resulting in a smaller proportion of the area of the cathode and the anode, which will reduce the corrosion rate.