Alina Sutygina

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.

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.

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.

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.

Effect of bias potential on the structure and distribution of elements in titanium-nitride coatings obtained by cathodic-arc deposition

It is shown that a change in the pulsed bias potential in the process of the cathodic-arc deposition of titanium nitride has a significant effect on the structure and composition of coatings, as well as on the quantity of the microdroplet fraction. A bias potential of above 50 V leads to a decrease in the coating growth rate, which is related to resputtering of the coating by ions accelerated from the plasma.