Institute of Materials Science of Khabarovsk Science Center of Far Eastern Branch of Russian Academy of Sciences, Khabarovsk, Russia:

S. A. Pyachin, Deputy Director for Science, Head of Laboratory of Functional Materials and Coatings, e-mail: pyachin@mail.ru
A. A. Burkov, Researcher

This paper shows the results of surface modification of titanium alloy VT20 by electric charge treatment in various gases such as argon, nitrogen and air. The composition and structure of modified surface layers were studied by optical microscopy, scanning electron microscopy and X-ray diffraction. Anode mass decreases and cathode mass increases at electric-discharge treatment, which is the evidence of metal transfer from anode to cathode. With increasing the discharge-pulse length from 100 to 500 μs, the erosion rate of anode increases, therefore the weight of cathode gain increases. The mass transfer coefficient reaches 80–85%. The thickness of the modified surface layers is 10 to 70 μm. The effects of electrical discharges in nitrogencontaining gases cause the saturation of titanium-alloy surface with titanium nitride. As increasing the duration of discharge impulses, the concentration of TiN in the surface layers of titanium alloy increases. The microhardness of the modified surfaces is higher in 9–16 times in comparison with the microhardness of untreated titanium substrate. The microhardness decreases gradually, moving from the surface deep into titanium alloy. The surface layer, obtained by the electric charge treatment in air, is a little harder than it processed in nitrogen. When the discharge-pulse length exceeds 300 μs, titanium oxide TiO is formed on the surface of the alloy processed in air, therefore the microhardness of this layer decreases. Testing the microabrasive wear of the surface layers according to the “rotating sphere–plate” method, established that the surface of titanium alloy treated in argon has a heterogeneous structure with high density of pores, and is eroded quickly during wear. At friction, the surfaces of titanium alloy processed in air and nitrogen are destroyed slower in factor of 3–5 compared to the unmodified
alloy and the sample prepared by the discharge treatment in argon due to hardening by titanium nitride.

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