Insufficient corrosion resistance of magnesium alloys limits their technical and medical applications. It is known that the corrosion rate of these materials depends, among other things, on the orientation of the samples relative to the workpieces, for example, rods or sheets obtained by thermomechanical processing. There is an opinion in the literature that this is primarily due to the influence of crystallographic texture. In this work, the corrosion resistance of samples cut from extruded rods of industrial alloys ZK60 and AZ31 along and across the extrusion direction was investigated. The corrosion rate was determined by the loss of weight and volume of the samples, as well as by the volume of hydrogen released when they were dissolved in a 0.9

Self-dissolving medical implants, such as screws for bone fracture fixation or vascular stents, represent a promising application of magnesium alloys. Magnesium-based bioresorbable materials are currently not only the subject of research by scientific groups worldwide but also the raw material for producing commercial products—medical metallic implants that are actively used in patient treatment. Nevertheless, many technological issues remain unresolved. Chloride-containing fluxes are widely used in casting magnesium alloys. It is unclear whether the presence of flux particles in materials for bioresorbable implants poses a risk of corrosion damage to the surface of the product. This study investigates the processes of initiation and development of filiform corrosion caused by the presence of a chloride-containing particle on the metal surface. Energy-dispersive spectroscopy was used to determine the composition of corrosion products, and Kelvin probe atomic force microscopy was employed to measure their electrode potential relative to the magnesium matrix. It was shown that, under ambient temperature of 25°C and 30

The combustion synthesis was used to prepare ZnO powder from solution of glycine as fuel and zinc nitrate as precursor and oxidizer, as well as for doping ZnO with one of the elements Fe, Co, Cu, and Mg the concentration of which was from 0.1 to 10 wt.% using their nitrates, to enhance ZnO photocatalytic activity in the decomposition of phenol under ultraviolet and visible light irradiation. As-synthesized ZnO was strong contaminated with free and bound carbon (10 - 30 wt.%) but after air calcination (1 h, 650 degrees C), the carbon content reduced to the level of 1 wt.%. The calcinated and doped ZnO powder consisted of individual highly dispersed (<1 m) nano-sized and submicron ZnO particles with a crystallite size of about 30 nm and sintered porous agglomerates ranging in size from 0.2 to 100 mu m. Of all dopants, only Mg improved the photocatalytic activity of ZnO powder in the decomposition of phenol under ultraviolet irradiation. The powder with 1 wt.% Mg showed the greatest increase in the activity reducing the time of almost complete decomposition of phenol by more than 2 times: from 3.75 - 5 h to 1.75 - 2.25 h. However, Mg-doped ZnO was not effective under action of visible light.

Biocompatibility makes magnesium alloys attractive functional materials in terms of their use as biodegradable implants. However, the technologies for manufacturing semi-finished products carry a possible diversity of the local strain rate and temperature within a rather wide range, which affects the processed material structure and properties. The purpose of the study is to determine the range of temperatures and resistance to deformation, at which there is no negative effect on the main structural characteristics of the processed material, using the example of a medical purposes alloy of the Mg–Zn–Y alloying system. The authors carried out mechanical tests of a biodegradable Mg–1Zn–2.9Y magnesium alloy at various temperatures and strain rates. The influence of temperatures in the range of 20...400 °C on the structure and properties of the Mg–Zn–Y system alloy is disclosed. Starting from a temperature of 350 °C, the process of dynamic recrystallization is accompanied both by the complete restoration (return) of the original microstructure and by coarsening of the grain size, which can adversely affect the material functional characteristics. The high thermal stability of the biodegradable Mg–1Zn–2.9Y magnesium alloy is revealed, which probably results from the presence of the LPSO phase in it. The study shows that the deformation process is accompanied by twinning. At a strain rate of 2∙10−2 s−1 over the entire temperature range, the grain size distribution slightly narrows and shifts towards smaller diameters. The application of the obtained results in technological processes for manufacturing medical semi-finished products will help to solve the issue of microstructure instability at the stage of transition from a semi-finished product to a finished product during subsequent thermomechanical treatments.

We investigate the effect of different types of thermo-mechanical treatment on the microstructure, corrosion, mechanical performance in air, and stress corrosion cracking (SCC) susceptibility of low-alloyed biodegradable Mg-Zn-Ca alloy. The as-cast ZX10 alloy in the heat-treated state (HT) was processed by extrusion or multiaxial isothermal forging (MIF). The microstructure of the obtained materials was investigated with the aid of scanning electron microscopy (SEM) powered by electron-backscattering diffraction (EBSD) and energy dispersive spectroscopy (EDX) techniques. The specimens after heat treatment, extrusion and forging were subjected to immersion testing in Hanks' solution to assess the corrosion rate as well as to slow-strain rate tensile (SSRT) testing in air and Hanks' solution to evaluate the SCC susceptibility. It is found that ultrafine-grained microstructure featured by a high fraction of low-angle dislocation boundaries created in the course of MIF demonstrates remarkably higher SCC resistance if compared to that of the extruded alloy characterized by fully recrystallized equiaxed grains having no appreciable low-angle substructure. It is suggested that the SCC performance of the MIF-processed alloy can be further enhanced through the microstructure control of its corrosion rate, which is found greater than that of the extruded alloy due to the presence of nanosized precipitates of the noble ternary secondary phase.

According to the stable opinion, hydrogen absorbed by magnesium alloys during corrosion can cause their stress corrosion cracking. One of the characteristic markers indicating the involvement of diffusible hydrogen into the fracture mechanism of metals is the negative strain rate dependence of the embrittlement degree. Recent studies show that the loss of ductility of the ZK60 alloy specimens subjected to a short-term (1.5 h) pre-exposure in a corrosive medium actually decreases with the increasing strain rate. However, after the removal of corrosion products from the surface of specimens, the strain rate dependence of the ductility loss becomes positive, which indicates the absence of hydrogen in the bulk of a metal. At a short-term exposure in a corrosive environment, the deep penetration of hydrogen into a metal could be limited due to the insufficient time for hydrogen diffusion. The paper studies the mechanical behavior of the ZK60 alloy subjected to a longer (12 h) pre-exposure in a corrosive medium followed by tensile testing in air at various strain rates. The authors consider the effect of strain rate, long-term pre-exposure in a corrosive medium, and subsequent removal of corrosion products on the strength, ductility, stages of work hardening, and localized deformation, as well as on the state of the side and fracture surfaces of specimens. The study identified that the ductility loss of specimens pre-exposed in a corrosive medium for 12 h decreases with the increasing strain rate, regardless of whether the corrosion products have been removed from their surface or not. It is shown that in this case, the negative strain rate dependence of the ductility loss is associated not with hydrogen dissolved in the bulk of a metal but with the presence of severe corrosion damage of the specimens’ surface. The authors proposed an explanation for the effect of corrosion damage on the mechanical properties and their strain rate sensitivity.

The microstructure and mechanical and acoustic properties of copper samples in the initial state and after barocryodeformation in different modes are studied. It is shown that cryogenic temperatures facilitate significant grain refinement due to the activation of mechanical-twinning processes; a homogeneous structure with an average grain size of 5–8 µm is formed. Barocryodeformation at temperatures of up to 125 K leads to a decrease in plasticity and a significant increase in hardness. A further decrease in temperature, on the contrary, contributes to a significant increase in plasticity, as well as a decrease in hardness. A correlation is noted between the median frequency of acoustic emission and the hardness value at all barocryodeformation temperatures.

The kinetics and fractographic features of stress corrosion cracking (SCC) in ZK60 and AZ31 alloys was investigated. It is established that ZK60 alloy possesses higher SCC resistance and fracture toughness compared to those of AZ31 alloy as is evidenced by the higher threshold stress intensity factors K1SCC and Kc. However, the lower average velocity of the stable SCC is observed in AZ31 alloy than in ZK60 one. Stable SCC occurs in two sub-stages, the first of which is featured by the lower crack growth rate and brittle fracture mode, while the higher crack velocity and quasi-cleavage fracture mode herald the second sub-stage. The crack growth velocities at specific SCC stages as well as stress intensity factor Kf associated with the alternation of the fracture mode are evaluated.

The tensile behaviour of magnesium alloy Mg-2Zn-0.1Ca (in wt.%) in the fine-grained state, obtained by multiaxial isothermal forging, has been investigated in a wide range of temperatures (20 divided by 350)degree celsius and strain rates (5 x10(-4)divided by 2 x10(-2)) s(-1) with the measurements of acoustic emission (AE). The dependences of mechanical properties and AE on the test temperature and strain rate were obtained and discussed. It has been established that at temperatures of 200 and 250degree celsius, a dynamic recovery mechanism is realized. The activation energy of the dislocation recovery is calculated, which sharply decreases with increasing strain rate.

The solution combustion synthesis (SСS) was used to prepare ZnO from mixtures of solutions of zinc nitrate (oxidizer) and citric acid (fuel) with different fuel-to-oxidizer ratio, as well as for doping ZnO with one of the elements Fe, Co, Cu, and Mg whose concentration was 0.1, 0.3, 1, 3, 10, and 15 wt

Magnesium alloys are among the most advanced structural materials in aviation and mechanical engineering industry due to their low density and high strength-weight ratio, but their ability to ignite at temperatures from 500 & DEG;C, while actively sustaining combustion, can cause disastrous consequences even in the event of minor emergencies. This paper is intended to investigate the compositions that can enhance flame resistance of magnesium alloys. Comparison was made between ignition temperatures of commercial cast alloy ML10, LPSO-structure alloy, advanced cast alloy with rare earth metals, and variations of these alloys with different additives - agents that improve flame resistance. It has been established that the maximum flame resistance is provided by those alloys that contain both the LPSO phase and the Yb or Ca additive as agents capable of raising the ignition temperature to 1000 & DEG;C or even higher.

Magnesium alloys preliminary immersed in a corrosion solution suffer from embrittlement, referred to as pre-exposure stress corrosion cracking (PESCC). It was suggested that PESCC can be attributed to the corrosion product film-induced stress (CPFIS), which is known to be responsible for SCC in many alloys. However, the internal stress associated with the formation of the corrosion products (CP) layer on Mg alloys have not been investigated as yet. Thus, in the present study, the internal residual stresses of the first and second kinds were assessed in the alloy ZK60 exposed to the corrosion solution, using the deflection of the thin plate and by the X-ray diffraction technique, respectively. It is found that the deposition of CP on the surface of the alloy ZK60 creates the compressive internal stresses of both kinds — I and II. The macro residual stress of the kind I in the thin plate is found to be not exceeding 3 MPa, while the micro residual stress of the second type in the surface layer of 20 – 30 µm can be as high as 290 MPa and cause plastic deformation of the bare metal with the internal stress which cannot be relieved by the removal of CP.

Using the example of assessing the technical condition of the trunnions of drying cylinders in cardboard machines (CBM), the question of the possibility of ranking cyclically loaded elements of dynamic equipment according to the degree of damage to their material by fatigue cracks using acoustic emission (AE) measurements is discussed. As a result of special laboratory studies with varying loads in the cycle of loading and lubrication of crack edges, the features of AE due to the friction of crack edges and plastic deformation at the crack tip during its growth in a viscous material have been established. It is shown that during cyclic loading of the material, AE signals from the friction of its banks are detected more steadily than AE signals due to a crack jump with an increase in its length, and that tracking the former ensures the detection of fatigue damage in the material even under loading conditions insufficient for crack growth. Based on the data obtained, three AE signs of the presence of fatigue damage in the material of the elements of dynamic equipment were developed under the condition of cyclic activation of the movement of crack edges. As a result of industrial testing of the developed AE signs, their operability was confirmed, their boundary values on the operating trunnions of CBM drying cylinders were clarified, and a method for ranking trunnions by the level of damage due to fatigue cracks was proposed. By comparing the results of AE measurements with ultrasound testing, the reliability of the proposed approach was evaluated and showed the probability of detecting a fatigue crack in the trunnions of CBM drying cylinders at the level of 71%, with the probability of skipping and false rejection of the product of 12 and 17%, respectively. The developed technique is also transferable to other massive dynamic equipment after clarifying the boundary values of AE signs of fatigue damage in the material on this type of facilities.

The chemical route for synthesis of magnesium nanoparticles serving as an active material for the nanocomposite anode with the conductive polymeric matrix is described. The electrochemical characteristics of the produced anode is investigated and compared with those of the counterpart anode made of micro-scale Mg particles. The energy density at 10 mA for the anode incorporating Mg nanoparticles (169.1 & PLUSMN; 10.8 W & BULL;h/kg) is 6.8 times higher than that for the anode with Mg microparticles (24.8 & PLUSMN; 6.7 W & BULL;h/kg). It is shown that the nanocomposite anode possesses superior stability and discharge voltage in potassium chloride aqueous solution with respect to that incorporating coarse particles. High discharge voltage is kept due to the uniform distribution of agglomerates of Mg nanoparticles in the anode. Using the results of Fourier-transform infrared spectroscopy it is suggested that the high resistance to oxidation of anode with Mg nanoparticles can be the root-cause of the enhanced electrochemical performance of the anode.

The results of mechanical tests of magnesium alloys of ternary systems promising for medical applications, Mg–Zn–Ca and Mg–Zn–Y, are presented. A peculiar temperature and strain-rate sensitive behavior of the stress-strain curves is discussed, in particular, a simultaneous significant increase in the plasticity and a decrease in the interval of stable plastic flow with the increasing temperature. The experimentally obtained value of the dislocation annihilation activation energy is expected to predict the true plastic strain corresponding to the point of plastic flow stability loss at different test temperatures. The prospects for a possible use of the results in technological processes for the manufacture and operation of medical devices are discussed.

Magnesium biodegradable alloys are a promising material for self-dissolving surgical implants. Magnesium is known to be sensitive to electrochemical corrosion due to the galvanic effect between the matrix and particles of secondary phases and inclusions. Another important factor is the pH level. The behavior of certain chemical reactions depends on the pH level, so one can assume that the pH level of a corrosive medium at the material surface is a factor determining what chemical reactions can occur there. Finally, there is evidence that variability of the crystallographic orientation of the grains may be a cause of anisotropy of corrosion properties. The purpose of this work is to reveal the influence of the electrode potential of the microstructural elements, the crystallographic orientation of the grains, and the pH level of the near-surface volume of the corrosion solution on the corrosion process. In the study, sections of 2×1.5 mm were marked on the ZX10 alloy samples, for which maps of the distribution of crystallographic orientations and chemical composition were drawn. To assess the influence of the electrode potential of the particles, the authors carried out a Kelvin probe mapping in the 90×90 µm area. Next, corrosion tests were carried out with video filming of the surface on the marked area. To determine the pH level influence, the solution circulation in the cell was varied. Upon completion of the tests, corrosion products and corrosion damage were examined in detail. According to the results, the pH level in the liquid near-surface micro-volumes has a greater influence than the electrode potential of the particles as it provokes the formation of corrosion products of a different composition, which leads to passivation of the surface areas around the particles. The authors identified two different types of filiform corrosion. For filiform corrosion, a correlation between the corrosion direction and the crystallographic orientation of the grains was established.

The paper presents the results of mechanical tests of promising magnesium alloys for medical use of ternary alloying systems Mg-Zn-Ca and Mg-Zn-Y. The temperature and strain rate sensitivity features of the loading curves are discussed, in particular, the simultaneous significant increase in plasticity and a decrease in the interval of stable plastic flow with increasing temperature. The experimentally obtained value of the activation energy of the dislocation annihilation will make it possible to predict the true plastic deformation corresponding to the point of loss of plastic flow stability at various temperatures. The prospects for the possible use of the obtained results in technological processes for the manufacture and operation of medical devices are discussed.

Self-resorbable implants made of magnesium alloys, unlike the traditional implants made of titanium alloys and stainless steels, have the ability to completely dissolve in the human body, which makes it possible to eliminate the need for a recurrent operation to extract them. The issue of the possibility of using magnesium implants in the combination with products made of titanium alloys remains insufficiently studied at the moment. At the same time, it is widely known that the elements such as titanium and iron, with a potential more positive than magnesium, have a disastrous influence on the corrosion of magnesium alloys, since magnesium dissolves much faster due to the galvanic effect. This work is aimed to determine how the distance to a titanium implant affects the corrosion rate of a ZX10 magnesium alloy sample with an ultra-fine grain structure. As it is an issue of medical application, the authors carried out the corrosion tests within the conditions simulating the human body conditions: the corrosion medium circulation and keeping temperature within 37±1 °C. The authors used physiological solution as a corrosion medium. During corrosion testing, a titanium implant was placed in three, six, and twelve centimeters from the magnesium alloy sample; and the control tests were also carried out without a titanium implant. According to the obtained data, at a distance of 3 cm, the galvanic effect between titanium and magnesium manifests itself strongly, increasing the corrosion rate and the size of corrosion damage, but at a distance of 6 cm, the titanium implant does not have a visible effect on the corrosion of a sample.

To assess the possibility of using the acoustic emission method in the direction of selecting activators of hydrodynamic processes of rotary apparatuses (machines) for processing liquid media in constrained conditions, experimental studies of hydrodynamic and acoustic effects accompanying two main modes of their application were carried out: the first is operation in the mode of activator frequency cyclic change, the second is operation in the mode of fixed activator rotation frequency. Seven forms of hydrodynamic activators of three types (vane, turbine and disk) and a rotary pulse apparatus applied for disinfection of lubricants were used in the research. Using conventional and high-speed video, the main hydrodynamic effects accompanying the operation of each type of activator were identified, which were compared with the established acoustic effects and measurements of temperature and the Reynolds centrifugal criterion. According to the results of the research, the possibility and limitations of using the acoustic emission method for comparing the effectiveness of activators and modes of liquid treatment in rotary pulse devices in conditions of its turbulent motion are shown. Under constrained operating conditions of activators imitated by the width of the working chamber, an acoustic emission peak never described in literature earlier was revealed, which differs from the noise accompanying the turbulent movement of the liquid. The relationship between the change in the amplitude of the peak of acoustic emission with the rate of change in the rotation of the activators and the rate of pumping the medium through the working chamber of the rotary pulse apparatus is also established. The results obtained can be used to select and compare the form of activators of hydrodynamic processes, as well as to select and maintain an effective mode of disinfection of aqueous solutions.