Vol 9, No 3 (2018)

This article discusses the influence of irradiation in the BN-350 fast neutron reactor on the mechanical properties and the thermal creep of 0.12C18Cr10NiTi austenite steel for the purpose of estimating the lifetime of structure materials with regard to long-term storage of spent nuclear fuel. Mechanical tests have been performed at 350 and 450°C. It is established that at 450°C the strength properties increase and the relative elongation decrease up to destruction, which is attributed to inverse α' → γ transformation intensely running in the irradiated steel at 450°C. With the temperature increase from 350 to 450°C, the rate of established creep of the irradiated steel increases by ~3.7 times. The amount and sizes of carbide inclusions generated upon long-term exposure at 450°C decrease, which can shorten the time of dry storage of spent reactor fuel assemblies.

The structure, phase composition, and mechanical properties of three-layer chromium-fulleritechromium films subjected to implantation with B⁺ ions (E = 80 keV, D = 5 × 10¹⁷ ion/cm²) are studied using the methods of atomic force microscopy, X-ray diffraction phase analysis, and nanoindentation. It is established that, as a result of ion implantation, the chromium and fullerite layers are intermixed and a solid-phase interaction occurs, owing to which a heterophase structure is formed with an increased nanohardness as compared with samples not subjected to implantation.

A technique for the formation of the quasi-porous structure of a Ti surface with craters that are formed by helium blistering was developed. It was found that the quasi-pores with a size of 10–50 μm were formed on the Ti surface because of flaking and exfoliation of blister domes under the implantation of He⁺ ions with an accelerating voltage of 100–200 kV and implantation fluence of 6 × 10¹⁷–6 × 10⁸ cm^–2. A subsequent irradiation with Ar⁺ ions in a carbon dioxide medium led to an increase in the microhardness of the quasi-porous Ti by 20–30%. The maximum increase in the microhardness was observed for the Ar⁺ ion fluence of 2 × 10¹⁶ cm^–2. It was shown that the fatigue strength of the Ti with the quasi-porous surface that was formed by the He⁺ implantation depended on the fluence of Ar⁺ ions and also had the maximum value at the fluence of 2 × 10¹⁶ cm^–2. The results obtained are explained by ion-induced modification of the structure and composition of the surface layers. In vivo experiments showed that the Ti implants with double implantation of He⁺ and Ar⁺ ions had enhanced biocompatibility and high osseointegration capacity of the surface.

The technique of deposition of polymer films from the barrier gas discharge plasma on top of dielectric substrates is developed. The film precursor is a monomer material highly dispersed in a transport plasma gas. The plasma formation of the continuous polymer film can be divided into two stages. The first stage is deposition of liquid monomer droplets with subsequent polymerization on the dielectric barrier surface resulting in growth of a discontinuous film. It is found that the ratio of the height of droplets to their lateral size is almost constant and for polystyrene it is equal to ~0.01. The second stage is expansion of the droplets into islands and their coalescence into a continuous polymer film on the dielectric barrier surface. The polymer coating thickness and the amount of cross bonds essentially depend on the current density and concentration of the monomer in the transport discharge gas. A continuous polymer film, which is not contaminated with the monomer destruction products, can be obtained in the current density range of 7–25 mA/cm². Experiments with several monomers, like methylmethacrylate, styrene and acrylonitrile, have shown that the growth rate is maximal for monomers with oxygen-free molecules. At the same time, a higher growth rate provides low cross-bond coatings, whereas to get high density of the cross-linked bonds one has to utilize low deposition rates. The minimal thickness at which continuity of the film is achieved increases when the monomer concentration in the plasma rises. In general, the coating thickness depends linearly on the discharge current density; the particular figures depend on the type and concentration of the monomer. The technological parameters are established and given for the three aforementioned monomers.

Experimental studies on the synthesis of aluminum oxynitride nanopowders in a reactor with a confined plasma jet by the interaction of disperse aluminum with ammonia and oxygen in a flow of nitrogen plasma generated in an electric arc plasma torch are performed. Preliminary calculations of the equilibrium compositions and thermodynamic characteristics of the multicomponent Al–O–N system are carried out. An optimal design of the reaction prechamber of the reactor is performed. Powders having a cubic structure and consisting of aluminum oxynitride phases with an average particle size in the range from 20 to 200 nm are obtained. It is established that the specific surface area of the obtained powders increases from 20 to 71 m²/g, and the nitrogen content in the nanopowders increases from 3.6 to 14.7 wt % with an increase in the flow rate of quenching gas from 1.8 to 6.0 m³/h. At the same time, the oxygen content decreases from 35.5 to 25.5 wt %. At a minimal flow rate of the quenching gas, the metallic aluminum and its oxide phases are present in the obtained powders. With an increase in the amount of quenching gas, the conditions for the mixing of aluminum vapors with oxygen and atomic nitrogen from decomposing ammonia are improved, which leads to the formation of aluminum oxynitride and aluminum nitride. The variation of the synthesis parameters allows us to obtain aluminum oxynitride nanopowders having a specific surface area ranging from 28 to 50 m²/g containing from 1 to 11 wt % of nitrogen and from 25 to 40 wt % of oxygen.

By means of XRD structural analysis and transmission electron microscopy, changes in the microstructure of TiAlN coatings deposited via magnetron sputtering after thermal cycling procedures (140 cycles) have been investigated. The thermal cycling procedure consisted in heating to 900°C and further cooling to room temperature. The sputtered target represented a 60 Ti–40 Al (at %) alloy. The coatings were deposited either onto a quenched austenitic steel substrate or onto the same substrate after preliminary Ti ion beam treatment. It is established that a layer of Ti and Al oxides with microcrystalline structure is formed on the coating surface in the course of thermal cycling. Compressive macrostresses under the oxide layer in the TiAlN coating decrease, whereas the heterogeneity of the Al distribution in the Ti_1–хAl_хN phase exhibits an increase. The preliminary Ti ion beam treatment of the substrate leads to an improvement of the coating thermal stability, to a decrease in the oxide layer thickness for the same number of thermal cycles, and to a wider Al concentration range in the Ti_1–хAl_хN phase of the surface coating layers.

Quaternary TiZrAlN and TiZrSiN films with Ti : Zr ratio of ~1 : 1 and different Al (or Si) content were deposited by simultaneous reactive magnetron sputtering of Ti, Zr, and Al (or Si) targets under Ar + N₂ plasma discharges. The elemental composition was determined by WDS and RBS methods; the phase composition was studied by X-ray diffraction. It was found that the c-(Ti,Zr,Al)N solid solution of substitution type is the basis of the (Ti,Zr)_1–xAl_xN (0.06 ≤ x ≤ 0.65) system. For the (Ti,Zr)_1–xSi_xN system (0.13 ≤ x ≤ 0.41), a dual-phase structure composed of a nanocomposite on the basis of the c-(Ti,Zr)N solid solution and grainboundary amorphous a-SiN_y phase is typical. Appearance of the second a-SiN_y phase promotes an amorphization of the films. Vacuum annealing of the films investigated at temperatures up to 1000°C does not lead to decomposition of the solid solutions which constitute the films. Both rather high deposition temperature (600°C) and stoichiometric nitrogen content can be the reasons for thermal stability of the films. Annealing-induced Al depletion of c-(Ti,Zr,Al)N solid solution grains is observed in (Ti,Zr)_1–xAl_xN films caused by the growth of the AlN based wurtzite phase at the grain boundaries.

The possibility of production of Ti-, N-, and C-containing superhard coatings on a metal substrate by a plasma-dynamic method in air is studied. The coating is deposited in the time of one short operating cycle of a magnetoplasma accelerator under the impact of a high speed electric discharge Ti-containing plasma jet on the substrate surface. Formation of TiN and TiCN nanostructured layers in the coating structure is ascertained with the help of the SEM and X-ray diffraction methods and it leads to the coating hardness increasing. Formation of a gradient layer of mixed material at the coating/substrate interface is found to occur under the action of a high-enthalpy plasma jet on a metal substrate. The value of hardness is not constant throughout the coating thickness, and ultrahigh nanohardness values >20 GPa were obtained for the subsurface layer and substrate/coating interface region. The mean value of hardness of the coating is 16.2 GPa. The coating produced has good adhesion with the substrate.

The elemental and phase composition, macro- and microstructure, hardness, and abrasive wear resistance of coatings obtained via a plasma sputtering of a high-speed steel (HSS) P6M5 powder and a (TiC + 50 vol % of P6M5) powder obtained using a self-propagating high-temperature synthesis procedure are studied. The structural state of oxygen and nitrogen impurities and their effect on the properties of coatings are considered. It is established that the metal-matrix structure of the composite powder remains unchanged in the sputtered coating, which causes a 2.0-fold and 7.6-fold increase in the hardness and wear resistance of the composite coating, respectively, in comparison with the coating obtained via sputtering of steel powder.

The ability to modify the surface microtopography of Al₂O₃ ceramic using nanosecond laser pulses is elucidated via atomic force microscopy. The characteristic shapes and sizes of laser-modified surface microstructures are determined. The effect of absorbed energy density and laser radiation wavelength on characteristic sizes of structures is shown as well.

Nanostructured composite materials (NCMs) based on Al–Mg alloy AMg6 (1560) modified with fullerene C₆₀ are obtained by milling of initial materials in a high-energy planetary ball mill and the subsequent hot extrusion of powder mixtures. The structure, phase composition, and physical and mechanical properties of NCMs obtained are studied. It is shown that introduction of 0.3 wt % of fullerene C₆₀ into NCMs prevents agglomeration of the particles during milling, intensifies the particle size reduction, and makes it possible to obtain an average aluminum crystallite size less than 50 nm. After consolidation of the powder mixtures by direct hot extrusion, the obtained materials demonstrate an increase in tensile strength up to 820 MPa and in bending strength up to 1.11 GPa. In this case, the density of NCMs is 2.61 g/cm³, which provides a value of the specific strength on the level of titanium alloys and fiberglass.

Photoluminescence spectra and kinetics have been studied for finely dispersed powders of such luminophores as SrAl₂O₄:(Eu²⁺,Dy³⁺) and Sr₄Al₁₄O₂₅:(Eu²⁺,Dy³⁺,B). Several lasers with different wavelengths (λ = 355, 404, 440 and 530 nm) were used for the excitation of photoluminescence. The photoluminescence of the materials is revealed to occur in a long-wave spectral range from 550 to 750 μm, which indicates the presence of energy levels, the radiative transitions between which form the radiation spectrum. The structure of the powders has been studied using a scanning electron microscope. It is established that the powder consists of microparticles (granules) up to 100 μm in size with a grain size up to 25 μm. According to the results of studies on the mechanoluminescence of SrAl₂O₄:(Eu²⁺,Dy³⁺) and Sr₄Al₁₄O₂₅:(Eu²⁺,Dy³⁺,B) powders, it is concluded that the mechanoluminescence is excited via an activation of traps when they interact with the electric fields of moving grain-boundary dislocations in the course of intergranular slipping during the deformation of microparticles under an impact load.

In the present work, the properties of Al₂O₃ nanocomposite prepared via spark-plasma sintering and reinforced with 0.5–2 wt % graphene are studied. Samples with different graphene contents are subjected to measurements of density, microhardness, coefficient of friction of composite–ruby, and frictional wear rate of composite. The fracture and wear track surface are inspected via fractography, and the composite as a whole is examined via X-ray diffraction. The graphene additive is established to increase the microhardness and to decrease the frictional wear rate by two orders of magnitude on account of absence of flaking of grains.

Sintered Nd–Pr–Dy–Fe–B permanent magnets were prepared by a powder blending technique using mixtures consisting of strip-casting alloy (wt %) 24.0 Nd, 6.5 Pr, 0.5 Dy, 1.0 B, 0.2 Al, 65.8 Fe and 2 wt % DyH₂ dysprosium hydride. After optimum heat treatment of magnets at 500°C for 1 h, the following hysteretic characteristics were reached: remanence B_r = 1.29 T; coercive force _jH_c = 1309 kA/m; critical field H_k = 1220 kA/m; and the maximum energy product (BH)_max = 322 kJ/m³. The characteristic peculiarity of the magnets prepared from hydride-containing power mixtures is the stability of hysteretic properties in the course of subsequent stepped annealings or progressive heatings at temperatures of 250–500°C for, in total, more than 20 h. Conditions of low-temperature annealings resulting in the degradation and subsequent restoration of hysteretic properties of magnets are determined. The evolution of the microstructure and phase composition of magnets in the course of heat treatments was studied by X-ray diffraction analysis and scanning electron microscopy, and the correlation between the structural changes and hysteretic properties of magnets is discussed.

Magnetic hysteresis and mechanical properties of a hard magnetic alloy Fe–27Cr–15Co–2Mo–V–Si–Ti in an isotropic and anisotropic state are investigated with the help of the method of design of experiments for the purpose of developing a new hard magnetic material with increased values of residual induction B_r (isotropic state) and coercive force H_cB (anisotropic state). Optimization of the modes of heat treatment is performed by the creation of central composite design 2³ + star points. Statistical analysis of the data obtained makes it possible to ascertain the standard Pareto charts for B_r, H_cB, and (BH)_max values for isotropic and anisotropic alloys. Nonlinear regression equations for dependences of B_r, H_cB, and (BH)_max on variation factors are obtained, on the basis of which optimal regimes of heat treatment are determined. Magnetic hysteresis properties of Fe–27Cr–15Co–2Mo–V–Si–Ti alloy are enhanced significantly after an optimal heat treatment. As a result, a new hard magnetic material on the basis of the Fe–27Cr–15Co system is developed. In the anisotropic state, the values of residual induction, coercive force, and maximum energy product are B_r > 1 T, H_cB > 50 kA/m, and (BH)_max > 24 kJ/m³, respectively, whereas in the isotropic alloy they are B_r ~ 0.8 T, H_cB ~ 40 kA/m, and (BH)_max > 11.5 kJ/m³. Analysis of magnetic properties of specimens from the produced pilot batch of anisotropic Fe–27Cr–15Co–2Mo–V–Si–Ti magnets in the number of 51 pieces shows that the yield of magnets with H_cB > 45 kA/m is 100% and with H_cB > 50 kA/m is 83%.

The possibility of modifying the surface of film implants of porous fluoroplastic by treating them with a low-temperature plasma of a high-voltage discharge with a nanosecond duration was investigated. The specimens were films for reconstructive surgery (FRS) and films for the replacement of bone defects (FRBD) from polytetrafluoroethylene (PTFE). The duration of the plasma treatment of the specimens ranged from 1 to 10 s. The surface quality of the films was estimated by their roughness and hydrophilic behavior using an atomic force microscope. It has been found that the plasma treatment significantly increases the surface roughness, which is associated with a change in its structure. The degree of the hydrophilicity of the surface of the FRS and FRBD films was determined by the roll-off angle of a water droplet and depended on the initial state of the surface (the smooth or corrugated side of the specimen), the gas discharge gap width, and the duration of the plasma treatment. A correlation between the roll-off angle of a water droplet and the proliferative capacity of the cells that were inoculated was found: the larger the roll-off angle, the higher the density of the cells observed on the surface. It has been found that the plasma treatment hardly affects the mechanical strength of the films and ensures the sterility of the films for 28 days after the plasma treatment for 1 s.

New methods for quantifying the contents of various zirconium forms in nickel, namely, zirconium solved in metal and zirconium in the form of ZrO₂, are developed using inductively coupled plasma atomic emission spectrometry. It is shown that, upon the introduction of 0.40 wt % ZrO₂ nanoparticles, the Zr ratio in a melt both in solution and in the form of ZrO₂ nanoparticles is 1 : 80, i.e., about 99% of Zr is in the form of ZrO₂. It was found that the ratio of nanoparticles in a composite material briquette affects the processes of nanoparticle assimilation by liquid metal, and ZrO₂ nanoparticles lyophobic toward nickel have a tendency for agglomeration with the formation of a high-temperature carcass.