Tkachuk O. Development of the methods of oxynitriding for improve wear- and corrosion resistance of titanium alloys.

Object of research: titanium alloys with nitride layers modified with oxygen. Purpose of work: determination of regularities of the regulated modification of nitride layers with oxygen and development of methods of oxynitriding to increase the wear- and corrosion resistance of titanium alloys. Methods of research: optical and electronic microscopy, durometerу, X-ray photography phase and micrororentgenospectral analyses, gravimetric and electrochemical polarization researches, tribotechnical tests, mechanical tests under static loading on short-time strength and plasticity, delayed destruction, fatigue tests on low-cycle pure bending, circulating bend. The range of the oxygen partial pressure 0,0001…0,1 Pa providing oxynitriding of titanium alloys by means of modification of nonstoichiometric titanium nitride with oxygen is determined. It is shown that modification of titanium nitride by oxygen is more intensive when the composition of titanium nitride is more similar to the lower limit of area of its homogeneity. The effect of oxynitriding is higher when the composition of titanium nitride is more close to the upper limit of area of its homogeneity. With decreasing oxygen partial pressure in the range of 0,0001…0,1 Pa and with the decrease of temperature of the modification beginning from 950 to 650оС the titanium oxynitrides of near equiatomic composition are formed. It assists the increase of the effect of oxynitriding. It is shown that by means of changing parameters of oxynitriding process it is possible to form the regulated phase-structural state of surface layers of titanium alloys. The bases of technology of oxynitriding to increase the wear- and corrosion resistance of titanium alloys in the high-concentration oxygen-containing acids under the saving high level of mechanical properties of titanium matrix are developed. The oxynitride coatings formed on VT6 titanium alloy on the developed technology were approved on the stands of ANTK "Antonov". The tests showed the increase of working capacity of friction units on 20-25%.