Effect of Irradiation with Si+ Ions on Phase Transformations in Ti–Al System during Thermal Annealing

The article deals with the effect of irradiation with Si+ ions on phase transformations in the Ti–Al system during thermal annealing. An aluminum film with a thickness of 500 nm was deposited on VT1-00 titanium samples by magnetron sputtering, followed by ion implantation. Samples before and after irradiation with Si ions were annealed in a vacuum of 10−4 Pa in the temperature range 600–1000 °C. It was established that ion implantation reduces the dissolution of Al in α-Ti with the formation of titanium silicides (TiSi2, Ti5Si3) and stabilizes aluminide phases Ti3Al rich in aluminum. As a result, a composite structure based on titanium silicide/aluminide was obtained on the surface of the sample synthesized by complex treatment: deposition, irradiation with Si+, and thermal annealing at the near-surface layers. The formation of the phase-structural state of the implanted layers is associated with the displacement of atoms of the crystal lattice, a result that is reflected in an increase in the size of the crystal lattice and a decrease in microdistortion of the lattice. The opposite effect is observed with increasing temperature. This fact is explained by the relaxation of unstable large grains with an excess of internal energies. At the annealing temperature of 900–1000 °C, a significant increase in microhardness was observed due to silicide phases.

СОСТАВ, СТРУКТУРА И ЭЛЕКТРОХИМИЧЕСКАЯ АКТИВНОСТЬ СИЛИЦИДА ТИТАНА В РЕАКЦИИ ВЫДЕЛЕНИЯ ВОДОРОДА

The phase composition and structure of titanium silicide have been investigated by X-ray diffraction and X-ray spectral microanalysis methods. It has been found that the investigated silicide is a singlephase system consisting of a high-temperature TiSi2 modification with a rhombic face-centered lattice. The cathodic behavior of the TiSi2 electrode has been studied by the methods of polarization and capacitance measurements. It has been found that the cathodic potentiostatic curves of silicide in solutions of 0,5 M H2SO4; 0,5 M H2SO4 + 0,005 M NaF and1,0 M NaOHhave Tafel sections with slopes of 0,120; 0,097 and 0,109 V and they are characterized by the values of the hydrogen evolution overvoltage 0,90; 0,64 and 0,74 V (at i = 1 A/cm2), respectively. Titanium disilicide in sulfuric acid solution belongs to materials with a high overvoltage of hydrogen evolution, but in a fluoride-containing sulfuric acid solution and in an alkaline solution - to materials with a low overvoltage of hydrogen evolution. Based on measurements of the differential capacitance of the TiSi2 electrode (at f = 10 kHz), it has been concluded that a thin silicon dioxide film (Si + 2H2O → SiO2 + 4H+ + 4e–)is present on the surface of the silicide in the acidic fluoride-free electrolyte.