Egor Kashkarov

Effect of Hydrogen Exposure on Mechanical and Tribological Behavior of CrxN Coatings Deposited at Different Pressures on IN718

In the current study, the properties of the CrxN coatings deposited on the Inconel 718 superalloy using direct current reactive magnetron sputtering are investigated. The influence of working pressure on the microstructure, mechanical, and tribological properties of the CrxN coatings before and after high-temperature hydrogen exposure is studied. The cross-sectional scanning electron micrographs indicate the columnar structure of the coatings, which changes from dense and compact columns to large columns with increasing working pressure. The Cr/N ratio increases from 1.4 to 1.9 with increasing working pressure from 300 to 900 mPa, respectively. X-ray diffraction analysis reveals a change from mixed hcp-Cr2N and fcc-CrN structure to approximately stoichiometric Cr2N phase. After gas-phase hydrogenation, the coating deposited at 300 mPa exhibits the lowest hydrogen absorption at 600 °C of all investigated coatings. The results indicate that the dense mixed cubic and hexagonal structure is preferential for hydrogen permeation resistance due to the presence of cubic phase with higher packing density in comparison to the hexagonal structure. After hydrogenation, no changes in phase composition were observed; however, a small amount of hydrogen is accumulated in the coatings. An increase of coating hardness and elastic modulus was observed after hydrogen exposure. Tribological tests reveal that hydrogenation leads to a decrease of the friction coefficient up to 20%–30%. The best value of 0.25 was reached for hydrogen exposed CrxN coating deposited at 300 mPa.

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.

The influence of nickel layer thickness on microhardness and hydrogen sorption rate of commercially pure titanium alloy

The influence of nickel coating thickness on microhardness and hydrogen sorption rate by commercially pure titanium alloy was established in this work. Coating deposition was carried out by magnetron sputtering method with prior ion cleaning of surface. It was shown that increase of sputtering time from 10 to 50 minutes leads to increase coating thickness from 56 to 3.78 μm. It was established that increase of nickel coating thickness leads to increase of microhardness at loads less than 0.5 kg. Microhardness values for all samples are not significantly different at loads 1 kg. Hydrogen content in titanium alloy with nickel layer deposited at 10 and 20 minutes exceeds concentration in initial samples on one order of magnitude. Further increasing of deposition time of nickel coating leads to decreasing of hydrogen concentration in samples due to coating delamination in process of hydrogenation.

Influence of the plasma-immersion ion implantation of titanium on the structure, morphology, and composition of the surface layer of Zr–1Nb alloy

The results of investigating the plasma-immersion ion implantation of titanium into Zr–1Nb alloy from arc-discharge plasma are presented. The investigations are performed using 1.5-kV bias voltage applied to the sample by means of a coaxial plasma filter for 5, 15, and 30 min. Scanning electron and atomic-force microscopy data demonstrate that, after implantation, grains with sizes of ~50–100 nm and craters with lateral sizes varying from ~1 μm to vanishingly small values are detected on the surface. Energy-dispersive X-ray spectroscopy data indicate the formation of an oxide film under titanium implantation. It follows from X-ray diffraction analysis that implanted titanium is in the dissolved state and the crystal-lattice-parameter ratio c/a increases after ion implantation. The layer-by-layer elemental analysis of the implanted layer performed via optical emission spectroscopy is evidence that the titanium-concentration maximum is shifted to larger depths with incresing implantation duration.

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.

Pulsed plasma-immersion ion implantation of aluminum into VT1-0 titanium

The results from investigating the pulsed plasma-immersion ion implantation of aluminum into VT1-0 titanium are presented. It is shown that variations in the elemental and phase composition of surface layers, their microscopic characteristics, and their mechanical properties as a function of implantation time are not monotonous but follow certain patterns. The possibility of interpreting the obtained data in terms of surface modification by metallic clusters with at least ~100 atoms generated in the gas of metal atoms evaporated from cathode spots is discussed.

Formation of titanium interlayer by vacuum arc deposition to increase the durability of titanium nitride coatings under thermal cycling conditions

It is found that the formation of a titanium interlayer between a zirconium alloy doped with niobium (Zr–1% Nb) and a magnetron-sputtered titanium nitride coating by means of cathodic vacuum arc increases the adhesion strength of titanium nitride. Titanium nitride coatings have a NaCl-type cubic lattice and are mainly oriented parallel to the (100) plane. Upon thermal cycling in the temperature range of 20–800°C, the structure of the titanium interlayer transforms from α phase to β phase. Ti–TiN coatings are stable upon thermal cycling in the temperature range of 20–800°C. The deposition of a titanium interlayer does not increase the hydrogen permeability of titanium nitride.

The investigation of hydrogenation influence on structure changes of zirconium with nickel layer

The results of experimental investigation of hydrogenation influence on structure changes of zirconium alloy (Zr-1%Nb) with thin nickel layer have presented in this work. Nickel layer was formed by magnetron sputter deposition. Hydrogenation was carried out at gas atmosphere at constant temperature. Different hydrogen concentrations were obtained by varying time of hydrogenation. Defect and phase structure was studied by means of X-ray diffraction, glow discharge optical emission spectroscopy, positron lifetime and Doppler broadening spectroscopies. New experimental data about the evolution of the positron annihilation parameters depending on hydrogen concentration in Zr-1Nb alloy with nickel layer was obtained.

Influence of Manufacturing Parameters on Microstructure and Hydrogen Sorption Behavior of Electron Beam Melted Titanium Ti-6Al-4V Alloy

Influence of manufacturing parameters (beam current from 13 to 17 mA, speed function 98 and 85) on microstructure and hydrogen sorption behavior of electron beam melted (EBM) Ti-6Al-4V parts was investigated. Optical and scanning electron microscopies as well as X-ray diffraction were used to investigate the microstructure and phase composition of EBM Ti-6Al-4V parts. The average α lath width decreases with the increase of the speed function at the fixed beam current (17 mA). Finer microstructure was formed at the beam current 17 mA and speed function 98. The hydrogenation of EBM Ti-6Al-4V parts was performed at the temperatures 500 and 650 °С at the constant pressure of 1 atm up to 0.3 wt %. The correlation between the microstructure and hydrogen sorption kinetics by EBM Ti-6Al-4V parts was demonstrated. Lower average hydrogen sorption rate at 500 °C was in the sample with coarser microstructure manufactured at the beam current 17 mA and speed function 85. The difference of hydrogen sorption kinetics between the manufactured samples at 650 °C was insignificant. The shape of the kinetics curves of hydrogen sorption indicates the phase transition αH + βH→βH.

Hydrogen-Permeability of Titanium-Nitride (TiN) Coatings Obtained via the Plasma-Immersion Ion Implantation of Titanium and TiN Vacuum-Arc Deposition on Zr−1%Nb Alloy

The surface of Zr‒1%Nb zirconium-alloy samples is treated with titanium via plasma-immersion ion implantation (PIII). Afterward, TiN coatings are deposited onto the implanted and initial samples by means of vacuum-arc deposition (VAD). Before and after each of the treatments mentioned above, changes in the hydrogen sorption rate, depth distribution of elements, and surface topography are investigated. It is found that separately performed VAD and PIII reduce the hydrogen sorption rate by a factor of 2‒15. At the same time, a combination of operations so that PIII is carried out before VAD decreases the sorption rate by one‒two orders of magnitude. It is revealed that the key parameter of the aforementioned methods affecting hydrogen permeability, the depth distribution of elements, and the surface topography is the bias value applied to the sample (substrate). In the case of our setup, the optimum biases of PIII and VAD are‒1500 and‒150 V, respectively.