No 3 (2019)

The paper deals with the problem of imbalance of a working element of high-speed technological devices, in particular, centrifugal units. The current trend in the development of technological devices is productivity improvement. The increase in the number of operating characteristics of the devices can be achieved through various ways: from the development of new types of devices and modernization of the existing ones to the improvement of frequency characteristics. Therefore, the issue of damping, which improves the reliability of technological machines, becomes more relevant in current technology. The study identified the most dangerous types of vibrations leading to the considerable damage of a working wheel. Based on the analysis of various axial vibrations influence on a working wheel, the authors proposed the way to eliminate vibrations using an adaptive damper. Axial vibration dampers working on permanent magnets have the following technical advantages over the mechanical dampers: relative high lifting capacity, high rotational speeds at high temperatures, no need for working fluid supply, etc. Magnetic dampers can operate at super high frequencies (more than 9000 r/min), therefore, it is necessary to study their work in the conditions close to limiting ones. The design adaptability is in the application of rubber-metal material, due to which the elastic force arises. The authors consider an integrated approach to damping: the force of magnetic interaction acts together with the elastic force. The aim of the paper is to determine the interrelations of key power characteristics. One of the necessary criteria of any system is its stability, which is evaluated in the paper using L.M. Lyapunov’s criterion. The paper presents the main results in the form of mathematical dependencies of a theoretical model.

Austenitic stainless steels are demanded alloys in modern industry due to their physical and mechanical characteristics. Concurrently, they are not devoid of weaknesses - strength properties do not meet the performance requirements for their use in the manufacture of essential components. One of progressing way to solve this problem is ion-plasma saturation with interstitials (nitrogen and carbon) of materials surface. In this paper, authors investigated the influence of pre-deformation microstructure with different density of deformation-associated defects on phase and elemental composition of surface layers formed during ion-plasma treatment in stable austenitic stainless steel (316L-type). It was shown that thermal-mechanical treatment in two regimes facilities to the formation of grain-subgrain structure submicrometer scale in specimens, in which main differences lie in the density of deformation defects and fraction of low-angle boundaries. It has been shown that during ion-plasma treatment in the mixture of gases (Ar + N2 + C2H2) at 540 °С (12 hours) of stable austenitic stainless 316L-type steel independently of initial microstructure (deformation-induced grain-subgrain with high density of defects or annealed grain-subgrain) in specimens surface layers with the same phase compositions were formed - supersaturated with nitrogen and carbon austenite and ferrite (Fe-γ_{N, C} and Fe-α_{N, C}), nitrides and carbonitrides Cr(N, C), Fe₄(N, C). The high density of non-equilibrium crystal defects promoted to the intensive saturation of the surface layers with nitrogen and carbon in austenitic stainless steel. The developed defective grain-subgrain structure in specimens contributes accumulation of interstitials (nitrogen and carbon) during ion-plasma treatment in the surface layer (≈ 5 μm) and suppression of bulk diffusion of carbon compared to the annealed grain-subgrain structure. The experimental results provide support for significant role of deformation-assisted well-developed microstructure in accumulation and bulk diffusion of interstitials under ion-plasma treatment of austenitic stainless steel.

At the moment, the issues related to the assurance of highly efficient thermal control in electronic systems continue to be relevant. More than half of the failure cases in the operation of electronic systems are caused precisely by the elevated temperature in the contact areas of their elements. Semiconductor components are installed on various plates or substrates that serve as elements of heat removal and provide effective thermal control. However, the selection of materials for such plates is a difficult task. Using the spark plasma method, the authors produced 3-D samples based on molybdenum and copper powders. The combination of copper with high thermal conductivity and molybdenum with a low-temperature coefficient of expansion makes it possible to use these metals as elements of heat removal for semiconductor components. According to the results of X-ray phase analysis, the authors identified that the composites, in addition to the main crystalline phases of molybdenum and copper, contain molybdenum carbide and molybdenum oxide. The presence of these chemical compounds is caused by the nature of the sintering process in graphite molds and the quality of raw materials. The authors identified that the dependence of the composites void density on the sintering temperature has a complex behavior related to the interchange of solid-phase and liquid-phase sintering. Scanning electron microscopy of samples showed that copper in samples fills in the intergranular space of molybdenum particles, and thus assure high density of end bulk products. In this case, sintering at a temperature of more than 1060 °C causes the runout of molten copper out of molds space that facilitates the formation of large pores with further sample density reduction. The study identified that, at sintering temperature of 1060 °C, the minimal number of pores appear in a sample, and the particles fit most closely to each other.

The development of biocompatible low-modulus β-alloys, in particular, Ti-Zr and Ti-Nb systems, became a new direction in medical materials science. The study of physicochemical and morphological properties and the structure of implants is one of the priority tasks of condensed matter physics and medical materials science. The search for the optimal set of coating parameters that provides the greatest mechanical and biological compatibility or inertness with bone tissue is one of the modern trends in the application of bio-coatings on a surface of metal implants. In the current work, the authors set and solve the problem of the formation of a bioinert Ti-Zr system coating using an advanced technique of electroexplosive deposition. Using the electroexplosion method, Ti-Zr composition coatings were produced on the surface of a titanium dental implant (VT6 alloy). The authors used scanning and transmission electron microscopy and X-ray diffraction analysis to determine the elemental and phase composition and to study morphology and defective substructure of the coating. Hardness and Young’s modulus, friction coefficient and wear resistance of the produced coating were determined. The formation of a Ti-Zr composition coating causes an insignificant (relative to a substrate without coating) decrease in the wear parameter (increase in wear resistance) of a surface layer (by 18 %), 1.5 times increase in the friction coefficient, a slight (3 %) increase in hardness, and a decrease in Young’s modulus by 64 %. It is established that the electroexplosive coating is multi-element and multi-phase; it has submicro- and nano-crystalline structure. High strength and tribological properties of the coating formed by the electroexplosion method are caused by the release of nanosized particles of the carbide and oxide phases detected by the X-ray phase analysis.

Modern materials science is developing towards the creation of functional materials with adjustable properties and parameters. The materials with electrically controlled optical properties, so-called electrochromic films, take the special place in the hierarchy of materials with adjustable parameters. The electrochromic films become widely used when creating a new generation of devices, both in various fields of electronics and in the field of renewable energy. From the practical point of view, one of the possible ways of improving technical characteristics of electrochromic films is their modification by carbon nanomaterials, in particular, by graphene oxide (GO) and reduced graphene oxide (rGO). The use of GO and rGO as a modifier for the electrochromic materials is caused by some unique features, namely: low sensitivity to ultraviolet radiation, chemical inertness, high specific surface area, the ability to change the charge state, and the increased electrical conductivity of rGO. To produce the electrochromic films, the authors used the spray-pyrolysis method. This method allows for obtaining the electrochromic films based on nanoscale tungsten trioxide (WO₃) modified by rGO. The authors studied the electrochemical characteristics of electrochromic films and the influence of rGO on the performance of the electrochromic films. The WO₃/rGO electrochromic films were reversibly colored in violet at the voltage of -2.1 V, as well as increased light transmission coefficient at the positive voltage of +2 V. During the research, the authors studied spectral properties of the produced nanocomposite WO₃/rGO electrochromic films at various values of electrical potential and evaluated their stable cycling within the range of voltage from -0.7 to 1 V for the three-electrode system. The study identified that the controllable activation of WO₃/rGO electrochromic films related to the increase in light transmission is in the voltage range from -1.6 V to -2.2 V, and the inverse effect is peculiar for the range from 0 to +2 V.