The superplastic behavior of ultrafine-grained (UFG) alloys Al-6% Mg-0.12% Sc-0.10% Zr-0.1% X, where X = Yb (alloy 1 (Yb)), Er (alloy 2 (Er)), and Hf (alloy 3 (Hf)), was studied. The objects of comparison were alloys Al-6% Mg-0.12% Sc-0.20% Zr (alloy 4 (Zr)) and Al-6% Mg-0.22% Sc-0.10% Zr (alloy 5 (Sc)). The effect of a simultaneous increase in the flow stress and elongation to failure in the superplasticity mode has been found. The maximum elongation to fracture in UFG alloys 1 (Yb) and 2 (Er) is observed at lower deformation temperatures than in alloys 4 (Zr) and 5 (Sc). The superplastic characteristics of alloy 3 (Hf) exceed those of alloys 4 (Zr) and 5 (Sc) with an increased content of alloying elements (in at %). UFG alloy 1 (Yb) at low temperature (400 degrees C) has good ductility (delta = 910%). The effect of the type and concentration of alloying elements on the deformation behavior and grain growth in UFG alloys Al-6% Mg is analyzed. With the superplasticity of UFG alloys, there is competition between strain-induced grain growth and dynamic recrystallization. It is shown that the fracture of UFG alloys under superplasticity is caused by the formation of pores on large Al3X particles.

The paper demonstrates for the first time the possibility of using an unalloyed tungsten powder with a spherical particle shape from 5 to 45 μm with a grain size of 0.5 to 2 μm obtained using plasma chemical synthesis, granulation, and spheroidization technologies to create products using additive technologies. The influence of the technological parameters of the selective laser melting (SLM) process on the physicomechanical characteristics and microstructure of test samples made of unalloyed tungsten powder has been studied. It is shown that the SLM parameters have a significant effect on the formation of the microstructure of test samples. It has been experimentally proved that, at optimal parameters of the SLM process, a homogeneous equiaxed microstructure with an average grain size of about 10 μm is formed in the samples. It was found that the maximum value of the Vickers hardness of the studied SLM samples of unalloyed tungsten is 310 HV10; the maximum value of microhardness is 4.1 GPa. The maximum density value of the obtained samples is 19.1 g/cm3 (relative density is 99.2

The features of spark plasma sintering of submicron Al2O3 powders with different contents (0, 0.5, 1.5, 5 vol

Al-6%Mg-Sc-Zr alloys with the total ratio of Sc + Zr = 0.32 wt.% make up the target of this research. The content of scandium and zirconium varied with an increment of 0.02%. The alloys were produced by induction casting. Their ultrafine-grained (UFG) microstructure was formed with Equal Channel Angular Pressing (ECAP). Such cast alloys have a homogeneous macrostructure formed by small equiaxed grains in the central part of the ingot and columnar crystals along the edges of the cross section. After ECAP, the average grain size in the alloy specimens is 0.5–1 µm. The average grain size does not depend on the ratio of Sc and Zr in these alloys. Superplasticity tests were performed at temperatures ranging from 300 to 500 °C and at a strain rate varying between 3.3·10-3 and 3.3·10-1 s-1. UFG Al-6%Mg-0.20%Sc-0.12%Zr and Al-6%Mg-0.18%Sc-0.14%Zr alloys exhibit the highest superplasticity. It was suggested that changes in Sc:Zr ratio affect spatial distribution and composition of the following precipitating particles: Al3Sc, Al3Zr, Al3(ScxZr1-x). An increase in Zr concentration is shown to reduce the susceptibility of UFG alloys to cavitation fracture.

Extensive studies of the physical, mechanical and fatigue properties of Ti-6Al-4V titanium alloy samples produced selective laser melting and hot rolling technology have been carried out. For each type of samples the values of the yield strength, tensile strength, elongation to failure, yield strength under compression, microhardness, Young's modulus and density were obtained. In particular, it is shown that the strength limit of the samples produced by selective laser melting is 1300 MPa and exceeds by 30% the corresponding value for samples produced by hot rolling. The density of samples produced in optimal modes of selective laser melting reaches 99,3% of the density of samples produced by hot rolling. Low-cycle fatigue curves are got for Ti-6Al-4V titanium alloy samples produced by selective laser melting and hot rolling. A comparison of the nature of failure on samples produced by these technologies is carried out. It is shown that at high cycle stresses (more than 900 MPa), the fatigue life of samples produced by selective laser melting significantly exceeds the endurance of samples produced by hot rolling. A material with such properties can be used in products (parts) that work for a short time under extreme overload conditions. High values of strength characteristics are associated with a thin needle-like microstructure of the martensitic type with a high content of a'-phase, which is formed in the process of layered laser fusion due to the high crystallization rate, which can reach 105-107 K/s. The paper demonstrates the possibilities of the selective laser melting to creating a promising titanium alloy for the manufacture of Ti-6Al-4V osteointegrable medical devices with characteristics corresponding to or exceeding the characteristics of the material obtained by the traditional hot rolling method.

Samples of unalloyed titanium VT1-0 with high strength characteristics (ultimate tensile strength of 820 MPa), which exceed the values for this material manufactured using conventional technologies, were produced by selective laser melting. To solve the problem of substitution of titanium alloys with commercially pure titanium in medical applications, unalloyed titanium VT1-0 with record mechanical characteristics (ultimate tensile strength of 1350 MPa) was processed by selective laser melting and rotary swaging. This value exceeds the characteristics of the highstrength Ti – 6 % Al – 4 % V alloy. The fine-dispersed martensite formed as a result of high crystallization rates under optimal mode of selective laser melting is the reason for the strength characteristics increase of unalloyed titanium VT1-0.

Dynamic compressive tests of alumina samples with different grain sizes obtained by spark plasma sintering (SPS) of submicron- and micron-sized α-Al2O3 powders have been performed. The effect of heating rate (Vh), sintering temperature (Ts), holding time (ts), and cooling rate (Vc) on the hardness, crack resistance, and dynamic ultimate strength (σY) of Al2O3 has been studied. An amorphous layer of a nanometer thickness was on the surface of submicron powders in the initial state. The transformation of an amorphous structure with an excess free volume into a crystalline phase occurs upon the SPS process with the formation of dislocation-type defects at the grain boundaries, which induce long-range internal stress fields. It has been shown that nanopores less than 50–100 nm in size are observed at the grain boundaries of ceramics. It has been shown that the nonmonotonic pattern of the dependence of σY on the temperature and time of the SPS is due to the simultaneous change in the density, the nonequilibrium state of grain boundaries, and the grain size of the ceramic. It has been shown that a decrease in the degree of nonequilibrium of the grain boundaries of alumina due to an increase in the SPS temperature or an increase in the holding time makes it possible to increase the dynamic strength of alumina. It has been established that an increase in the cooling rate leads to the formation of compressive residual stresses and a slight increase in σY of the ceramic. The maximum dynamic strength (σY = 1755 MPa) was reached for the alumina ceramic with an average grain size of 1.6–2 μm obtained by SPS at Vh = 50°С/min, Ts = 1520°С, and ts = 50 min.

Bimetallic samples based on unalloyed titanium and titanium alloy have been obtained. The main disadvantage of the most common material for medical implants Ti6Al4V alloy is the danger of toxic elements of aluminum and vanadium entering the human body during implant wear. To solve this problem, it is proposed to use bimetallic products designed in such a way that the part interacting with human body is made of unalloyed titanium, and the inner part is made of a high-strength titanium alloy providing high mechanical properties. The technology of selective laser melting allows to produce similar products in one technological cycle. The aim of the research is a comprehensive study of the physical and mechanical properties and structure of the bimetallic material of the system “unalloyed titanium – alloy Ti6Al4V”obtained by selective laser melting. The melting modes have been optimized to achieve high mechanical characteristics. It is shown that the strength characteristics with optimal conditions correspond to the characteristic value of unalloyed titanium – the ultimate tensile strength was 860 MPa. Embrittlement of the micro-welded bimetal compound is not observed: tensile fracture occurs with the least durable component – unalloyed titanium. Metallographic studies have shown the absence of micropores, microcracks and other defects in the interface zone of the two materials and adjacent areas. Thus, selective laser melting makes it possible to obtain a new class of bimetallic medical devices with high physical and mechanical properties, while ensuring that living tissues do not contact with toxic elements.

The study provides a qualitative assessment of the maximum rate of metal powder processing, which ensures obtaining a high density product by selective laser melting. The maximum rate is determined by the characteristic times of the main physical processes for the formation of a solid material in the course of selective laser melting: heating, warming, melting, and spreading.

The investigation is focused on the impact of hydrogen on the physical and mechanical properties of 316L austenitic stainless steel (67.5Fe, 17.7Cr, 10.6Ni, 2.6Mo, 1.2Mn, 0.4Si in wt

The microstructure and mechanical properties at room and elevated temperatures of ultrafine-grained steel 08H18N10Т, obtained by the equal-channel angular pressing method (ECAP) at temperatures of 150 and 450 °C have been studied. It has been established that UFG steel has an increased content of α`-martensite and when it is heated, nanoparticles of the σ-phase are released. It has been shown that ultrafine-grained steel has high tensile strength and good ductility. A decrease in the Hall-Petch coefficient of ultrafine-grained steel was noted, which is due to the fragmentation of δ-ferrite particles during ECAP.

This paper reported the results of research into the effect of Equal Channel Angular Pressing (ECAP) temperature and 1-h annealing temperature on mechanical properties, stress-relaxation resistance, and corrosion resistance of austenitic steel AISI 321L with strongly elongated thin δ-ferrite particles in its microstructure. The formation of α′-martensite and fragmentation of austenite grains takes place during ECAP. Ultrafine-grained (UFG) steels demonstrate increased strength. However, we observed a reduced Hall–Petch coefficient as compared with coarse-grained (CG) steels due to the fragmentation of δ-ferrite particles. UFG steel specimens were found to have 2–3 times higher stress-relaxation resistance as compared with CG steels. For the first time, the high stress-relaxation resistance of UFG steels was shown to stem from a internal stress-relaxation mechanism, i.e., the interaction of lattice dislocations with non-equilibrium grain boundaries. Short-time 1-h annealing of UFG steel specimens at 600–800 °C was found to result in the nucleation of σ-phase nanoparticles. These nanoparticles affect the grain boundary migration, raise strength, and stress-relaxation resistance of steel but reduce the corrosion resistance of UFG steel. Lower corrosion resistance of UFG steel was shown to be related to the formation of α′-martensite during ECAP and the nucleation of σ-phase particles during annealing.

The microstructure and mechanical properties (at room and elevated temperatures) of ultrafine-grained (UFG) 08Kh18N10T steel fabricated by equal-channel angular pressing (ECAP) at temperatures of 150 and 450°C are studied. The UFG steel is found to have a high α' martensite content, and σ-phase nanoparticles precipitate in it upon heating. The UFG steel is shown to have a high ultimate tensile strength and good ductility. The Hall–Petch coefficient of the UFG steel is found to decrease due to the fragmentation of δ-ferrite particles during ECAP.

Comprehensive studies of the physical and mechanical properties and structure of VT1-0 titanium samples processed by selective laser melting have been carried out. High strength characteristics (the ultimate tensile strength of 820 MPa, the yield strength of 710 MPa) have been achieved. These values exceed by 2 times the values for this material produced using conventional technology. The formation of the martensitic αʹ-phase, obtained due to the high crystallization rates realized in selective laser melting process, is the reason for the increase in the mechanical characteristics of titanium VT1-0. Mechanical characteristics of titanium VT1-0 subjected to high-temperature annealing demonstrated a monotonous decrease in strength parameters by 15% and an increase in plastic characteristics by 30%. It is shown that the technology of selective laser melting makes it possible to solve the problem of improving the strength characteristics of unalloyed titanium to create a new class of medical devices.

Superplastic behavior of ultrafine-grained (UFG) Al-6Mg-0.12Sc-0.10Zr-0.1X alloys, where X = Yb (Alloy #1-Yb), Er (Alloy #2-Er), and Hf (Alloy #3-Hf), has been studied. The total content of Sc, Zr, Yb, Er, Hf in the alloys was 0.32 wt. Al-6Mg-0.12Sc-0.20Zr (Alloy #4-Zr) and Al-6Mg-0.22Sc-0.10Zr (Alloy #5-Sc). Their UFG microstructure was formed with ECAP. Two different types of deformation behavior during superplasticity were demonstrated. A simultaneous increase in yield stress and elongation to failure during superplastic deformation was discovered. High deformation temperatures were shown to cause a competition between dynamic (strain-induced) grain growth and dynamic recrystallization, leading to a finer grain microstructure. The values of strain hardening factor (n), strain rate sensitivity factor (m), and superplastic deformation threshold stress (Sp) were determined. The impact of the type and concentration of alloying elements on the deformation behavior and dynamic grain growth of Al-6 that the maximum elongation to failure in Alloy #1-Yb and Alloy #2-Er is observed at lower deformation temperatures than in Alloy #4-Zr and Alloy #5-Sc. The superplastic properties of Alloy #3-Hf are superior to those of Alloy #4-Zr and Alloy #5-Sc with high content of alloying elements (in at. manifests good elongation to failure (910 satisfiability of Hart's criterion for calculating uniform deformation value under superplastic conditions was verified. It was demonstrated that cavitation when pores are formed in large Al3X particles at high temperatures causes early failure of aluminum alloys.

Comprehensive studies of the physical and mechanical properties and structure of VT1-0 titanium samples processed by selective laser melting have been carried out. High strength characteristics (the ultimate tensile strength of 820 MPa, the yield strength of 710 MPa) have been achieved. These exceed by 2 times the values for this material produced using conventional technology. The formation of the martensitic α'-phase, obtained due to the high crystallization rates realized in selective laser melting process, is the reason for the increase in the mechanical characteristics of titanium VT1-0. Mechanical characteristics of titanium VT1-0 subjected to high-temperature annealing demonstrated a monotonous decrease in strength parameters by 15% and an increase in plastic characteristics by 30%. It is shown that the technology of selective laser melting makes it possible to solve the problem of improving the strength characteristics of unalloyed titanium to create a new class of medical devices. Keywords: unalloyed titanium, VT1-0, additive technology, selective laser melting, density, strength, plasticity, elastic modulus, microstructure, implants for surgery.

The results of experiments on the study of the physical and mechanical properties and microstructure of 316L stainless steel produced by additive technology selective laser melting are obtained. The dependences of the physical and mechanical properties (density, tensile strength, yield strength, elongation to failure, Young's modulus, nano hardness) of 316L steel on the main parameters of the selective laser melting (laser power, scanning speed) are obtained. 316L steel produced by selective laser melting has high mechanical characteristics: tensile strength – 710 MPa; yield strength – 610 MPa; elongation to failure – 48%; relative density – 99.5%, which is comparable to the values obtained for 316L steel produced by traditional methods. These characteristics were obtained using the optimal parameters of selective laser melting: laser power 100 W, scanning speed 200 mm/s, layer thickness 50 ?m, the distance between the scanning tracks is 80 ?m. It is shown that the use of the “volumetric energy density” parameter is usefully for carrying out a primary assessment of technological modes and solving the problem of optimizing the parameters of selective laser melting to obtain a material with high physical and mechanical properties. The nonlinear dependence of the mechanical properties of 316L steel on the main technological parameters can be explained by the influence of porosity arising at non-optimal modes. It is shown that selective laser melting allows controlling the porosity of 316L steel by varying the parameters of the technological mode. Thus selective laser melting makes it possible to produce both a material with a high density close to theoretical values and a material with controlled porosity.

Hot rolled commercial metastable austenitic steel 321 with strongly elongated thin delta-ferrite particles in its microstructure was the object of investigations. Ultrafine-grained (UFG) microstructure in steel 321 was formed by Equal Channel Angular Pressing (ECAP) at 150 oC and 450 oC. When heating the UFG steel specimens, the nucleation of sigma-phase particles blocking the grain boundary migration was observed. The maximum elongation to failure (~250%) was achieved at the deformation temperature 750 oC. The process of superplastic deformation of the UFG steel 321 is controlled by simultaneous grain boundary sliding and power-law creep. The contribution of each process depends on the grain growth rate in the superplasticity regime as well as on defect accumulation on the grain boundaries. The fracture of the UFG steel 321 specimens has a cavitational character - an intensive formation of large elongated pores at the non-metallic particles as well as of the submicron pores at the sigma-phase particles in the course of superplastic deformation were observed.

This research was undertaken to study the way deformation behaves in ultrafine-grained (UFG)-conducting Al-Zr alloys doped with Sc, Hf, and Yb. All in all, eight alloys were studied with zirconium partially replaced by Sc, Hf, and/or Yb. Doping elements (X = Zr, Sc, Hf, Yb) in the alloys totaled 0.4 wt.%. The choice of doping elements was conditioned by the possible precipitation of Al3X particles with L12 structure in the course of annealing these alloys. Such particles provide higher thermal stability of a nonequilibrium UFG microstructure. Initial coarse-grained samples were obtained by induction casting. A UFG microstructure in the alloys was formed by equal-channel angular pressing (ECAP) at 225 °C. Superplasticity tests were carried out at temperatures ranging from 300 to 500 °C and strain rates varying between 3.3 × 10−4 and 3.3 × 10−1 s−1. The highest values of elongation to failure are observed in Sc-doped alloys. A UFG Al-0.2%Zr-0.1%Sc-0.1%Hf alloy has maximum ductility: at 450 °C and a strain rate of 3.3 × 10−3 s−1, relative elongation to failure reaches 765%. At the onset of superplasticity, stress (σ)–strain (ε) curves are characterized by a stage of homogeneous (uniform) strain and a long stage of localized plastic flow. The dependence of homogeneous (uniform) strain (εeq) on test temperature in UFG Sc-doped alloys is increasing uniformly, which is not the case for other UFG alloys, with εeq(T) dependence peaking at 350–400 °C. The strain rate sensitivity coefficient of flow stress m is small and does not exceed 0.26–0.3 at 400–500 °C. In UFG alloys containing no Sc, the m coefficient is observed to go down to 0.12–0.18 at 500 °C. It has been suggested that lower m values are driven by intensive grain growth and pore formation in large Al3X particles, which develop specifically at an ingot crystallization stage.