N. N. Nikitenkov

Ionizing radiation-stimulated diffusion and desorption of hydrogen from metals

The processes of hydrogen diffusion from a sample depth activated by electrons with an energy of tens of keV are studied. The difference from the known models of electron-stimulated desorption, which consider as a rule electron energies from 0.5 to several keV, is noted. The proposed model is shown to correspond to at least two established experimental facts: the nonlinear dependence of hydrogen isotope desorption on the electron beam current density affecting the sample and the dependence of hydrogen desorption on the irradiation time of the sample.

The formation of stable hydrogen impermeable TiN-based coatings on zirconium alloy Zr1%Nb

TiN coatings were deposited by DC reactive magnetron sputtering (dcMS) method on Zr1%Nb substrates with different film thickness. The influence of crystalline structure and thickness of the coatings on hydrogen permeation was investigated. The results revealed that the increase in thickness of the film reduced hydrogen permeability. 1.54 μm TiN deposited in N2/Ar gas mixture with a ratio of 3/1 reduces hydrogen permeation in more than two orders of magnitude at 350 °C. Adhesion strength decreased with increasing film thickness (0.55 to 2.04 μm) from 7.92 to 6.65 N, respectively. The Ti underlayer applied by arc ion plating (AIP) leads to the formation of stable Ti/TiN coatings on Zr1%Nb under thermocycling conditions up to 800 °C. Meanwhile, hydrogen permeation rate of Ti/TiN deposited by combination of AIP and dcMS remains at the same level with TiN deposited by dcMS.

A plant for studying radiation and thermal desorption of gases from inorganic materials

A high-vacuum plant and methods for studying thermal and radiation-stimulated desorption from solid-state materials are described. Radiation-stimulated desorption was studied using an electron gun with a 1- to 120-keV beam energy, featuring a new technology of power supply units. Partial pressure gages with a sensitivity of up to 10−13 Pa were used to record mass spectra of residual gases. Results of studying thermal- and radiation-stimulated yields of hydrogen from submicrocrystalline samples of a BT-6 alloy are presented to demonstrate the serviceability of the created procedures.

Study of the plasma immersion implantation of titanium in stainless steel

The results of the study of the pulsed plasma-immersion ion implantation of titanium in steel Cr18Ni10Ti depending on the time (dose) implantation are presented. It is shown that the change of the element and the phase composition of the surface layers and their microscopic characteristics and mechanical properties (hardness, wear resistance) depending on the implantation time is not monotonic, but follows to a certain rule. The possibility of interpretation of the obtained results in the thermal spike concept of the generation on the surface by the stable (magic) clusters is discussed. This concept follows logically from the recent studies on the plasma arc composition and from a polyatomic clusters-surface interaction.

Study of coatings based on titanium oxides and oxynitrides using a set of methods

A set of methods has been applied to study the properties of titanium oxide and oxynitride coatings on steel. It is established that the coatings consist of two phases with a nanocrystalline and an amorphous structure with a high proportion (∼50 %) of grain boundaries; anatase is the dominant crystalline phase. The obtained results can be applied in the development of coatings for stents as well as for manufacturing hydrogen accumulators.

Dynamics of hydrogen accumulation and radiation-stimulated release from steels

Hydrogen accumulation during electrolytic saturation of 12Kh18N10T and 12Kh12M1BFR steels, as well as during thermally and radiation-stimulated hydrogen release from the same materials, was studied. It was shown that there is a critical hydrogen concentration in the sample, which is reached in 50 h for this saturation method (1 M H2SO4 electrolyte, current density is 0.5 A/cm2). Initially, hydrogen is trapped at low-temperature (400–500°C) traps of several types in surface layers. At saturation times of 50 h and longer, hydrogen penetrates to high-temperature (800–900°C) traps in the sample bulk. Under electron irradiation of saturated samples, the hydrogen yield nonlinearly increases with electron current density and energy above 40 keV. It was concluded that electronic processes (Auger process and plasmon excitation) play a dominant role in hydrogen diffusion and desorption activation.

Radiation-Enhanced and Thermostimulated Hydrogen Release from Palladium and Zirconium

The results of a mass-spectrometric analysis of hydrogen release from palladium and zirconium samples under the action of accelerated electrons (with an energy of 40 keV and a current density of 3 to 30 μA/cm2) and x-rays (with energies of 40 and 120 keV) are presented. The amount of hydrogen removed from these samples and the residual hydrogen content are monitored via the methods of mass-spectrometry and thermodesorption. The conclusion is made that substantial removal of hydrogen (up to 90% of the initial content) from the analyzed materials can be achieved under the action of electrons and x-rays. It is found that x-ray irradiation can ensure more efficient removal of hydrogen than electron bombardment.

Hydrogen absorption by Zr-1Nb alloy with TiNx film deposited by filtered cathodic vacuum arc

coating for Zr-2.5Nb alloy from hydrogenation. Dense TiNx films were prepared by filtered cathodic vacuum arc (CVA). Hydrogen absorption rate was calculated from the kinetic curves of hydrogen sorption at elevated temperature of the sample (T = 673 K) and pressure (P = 2 atm). Results revealed that TiNx films significantly reduced hydrogen absorption rate of Zr-2.5Nb.

Features of the plasma saturation of nanocrystalline and coarse-crystalline titanium samples with hydrogen and deuterium

We investigate the laws governing the saturation of nano- and coarse-crystalline Ti-6Al-4V alloy samples with hydrogen from high-frequency and glow discharge plasmas with a view to finding materials suitable for making hydrogen accumulators. We conclude that nanocrystalline Ti-6Al-4V alloy holds promise for creating hydrogen accumulators, and hydrogen plasma of high-frequency discharge origin is a cleaner hydrogen saturation medium than that of non-self-sustained discharge origin.

A laboratory device for measuring the diffusion coefficient of hydrogen in metals during their simultaneous hydrogenation and electron irradiation

An upgraded high-vacuum installation and procedure for studying diffusion of hydrogen in a BT1-0 titanium alloy membrane during irradiation of a sample by an electron beam with an energy of 10-120 keV in the scanning and stationary modes and with simultaneous electrolytic saturation are described. For this purpose, deflecting electrodes intended for scanning the beam are additionally integrated into the installation. The mass spectrum of the residual gases was recorded by the partial pressure sensors with a sensitivity as high as 10-13 Pa. The diffusion coefficient of hydrogen measured under the scanning action of the electron beam on the titanium membrane is given.