Luk'yanenko O. Thermo-diffusion processes' regularity in high vacuum and their influence on structure and proper ties of titanium alloys' surface layers.

The kinetics of interaction the industrial titanium alloys of different structural classes (alpha, pseudo-alpha, alpha+betta) with a gaseous environment at temperatures 923-1273 K and at 0,133…13,3 mPa are studied. Three types of interaction are detected: 1) prevailing gas-saturation; 2) gas-saturation accompanied by volatile oxides and their further sublimation; and 3) prevailing sublimation. The following kinetic parameters are defined: rate of gas saturation; activation energies. Certain structural and phase modification in near-surface layers under sublimation and gas-saturation have been confirmed to take place in a fine vacuum. A micro relief is formed on the alloy's surface; and the relief appearance depends on phase and chemical titanium alloy's composition. The diffusive saturation of metal near-surface layers by interstitial impurities change the hardness of the layers. The hardness gradient depends from structural and phase composition of the alloys. It is shown, that stresses, temperature c yclic changes and the "prismatic" texture accelerate thermal- diffusion processes on the surface and in the bulk of metal. Physical-mathematical model of high-temperature interaction of titanium alloys with vacuum environment is improved. The rate coefficient of phase-boundary reaction and its dependence's on pressure, temperature, metal's texture and stresses are defined. This allows to forecast the distribution of interstitial impurities in the near-surface layers of titanium alloys after vacuum heat treatments.