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.

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

Abstract—There are model for calculating the latent heat of fusion of pure metals, included the contribution of the phonon “analogue of the Casimir force” to the melting of metals. The model makes it possible to explain the mismatch between the experimental value of the latent heat of melting and the theoretically calculated sum of the jump in the configuration and vibrational entropy during the phase transition from solid to liquid. The described approach also makes it possible to estimate the magnitude of the volume change during melting using the values of the crystallogeometric and thermodynamic parameters of the material.

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.

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.

A model for calculating the latent melting heat of pure metals in the process of their fusion with consideration for the phonon “Casimir force” analogue is presented. The model makes it possible to explain the difference between the experimental and theoretically calculated specific melting heats by the sum of jumps in the configurational and vibrational entropies during the solid–liquid phase transition. The described approach also provides the possibility of estimating the volume jump under melting from the crystal geometry and thermodynamic parameters of a material.

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.

Unalloyed titanium VT10 with a record value of the ultimate tensile strength of 1350 MPa obtained using technologies of selective laser melting and rotary swaging. This value exceeds by 3 times the tensile strength of commercially pure titanium produced using conventional technologies and also exceeds the strength values of Ti6Al4V (grade 5) high strength titanium alloy. The reasons of the increase in the strength characteristics of titanium VT10 are the finedispersed marten site obtained due to high crystallization rates in the process of selective laser melting, and its additional refinement during the rotary swaging process. To study the thermal stability of the mechanical properties of titanium VT10 processed using various technologies, research of the effect of annealing temperature in the range of 100–800 °C on the ultimate tensile strength and elongation to failure were carried out. Results have shown that the dependence of the ultimate tensile strength on the annealing temperature for VT10 titanium samples after selective laser melting and rotary swaging has a threestage behavior. The ultimate tensile strength decrease by 25–35% after heat treatment at 800 °C. The values of elongation to failure for VT10 titanium samples processed by selective laser melting and rotary swaging monotonically increase from 8–12 to 18–23% when the annealing temperature grows up to 800 °C. The possibilities of methods of selective laser melting, rotary swaging and heat treatment to control the mechanical characteristics of titanium VT10, which is a promising material for the manufacture of osteointegrable medical implants, are demonstrated. The combined application of the abovementioned methods makes it possible to produce VT10 titanium with a given combination of strength and plastic characteristics in a wide range of values.

A phenomenological model has been proposed that allows the volume change on melting of metals to be related to the valence, thermodynamic properties, and crystallographic parameters of the solid phase. Basic to the model are ideas that a phonon "analog of the Casimir force" plays a key role in determining the metal melting process.

A model is proposed to explain the effect of the severe plastic deformation (SPD) temperature on the diffusion properties of the grain boundaries in ultrafine-grained (UFG) metals and alloys. It is shown that an increase in the SPD temperature in UFG metals leads to an increase in the activation energy of grainboundary diffusion from (3–5)k B T m, which corresponds to the diffusion parameters of nonequilibrium grain boundaries, to (8–10)k B T m, which corresponds to the diffusion parameters of equilibrium grain boundaries (k B is the Boltzmann constant, T m is the melting temperature). The dependence of the activation energy of grain-boundary diffusion on the SPD temperature is found to be determined by the kinetics of the competing processes of defect accumulation at grain boundaries and the diffusion accommodation of defects.

A model of the grain-boundary self-diffusion process in metals undergoing phase transitions in the solid state is proposed. The model is based on the ideas and approaches of the theory of nonequilibrium grain boundaries. It is shown that the range of application of basic relations of this theory can be extended, and they can be used to calculate the parameters of grain-boundary self-diffusion in high-temperature and low-temperature phases of metals with phase transition. Based on the constructed model, activation energies of grainboundary self-diffusion in titanium and zirconium are calculated, and their anomalously low values in the low-temperature phase are explained. The calculated activation energies of grain-boundary self-diffusion are in good agreement with experimental data.

Предложена модель процесса зернограничной самодиффузии в металлах, испытывающих фазовые переходы в твердом состоянии. В основе модели лежат идеи и подходы теории неравновесных границ зерен. Показано, что область применения основных соотношений этой теории может быть расширена, и они могут быть использованы для расчета параметров зернограничной самодиффузии в высокотемпературной и низкотемпературной фазах металлов с фазовым переходом. На основе построенной модели проведен расчет энергий активации зернограничной самодиффузии в титане и цирконии и дано объяснение их аномально низких значений в низкотемпературной фазе. Рассчитанные значения энергий активации зернограничной самодиффузии хорошо согласуются с экспериментом. Работа выполнена при поддержке РНФ (грант N 16-13-00066). DOI: 10.21883/FTT.2017.01.43942.118

Melting (crystallization), a phase transition from a crystalline solid to a liquid state, is a common phenomenon in nature. We suggest a new factor, “the Casimir force analogue”, to describe mechanisms of melting and crystallization. The Casimir force analogue is a force occurring between the surfaces of solid and liquid phases of metals caused by different energy density of phonons of these phases. It explains abrupt changes in geometry and thermodynamic parameters at a melting point. “The Casimir force analogue” helps to estimate latent melting heat and to gain an insight into a solid–liquid transition problem.

The thermal stability of the structure and the mechanical properties of submicrocrystalline (SMC) titanium alloy Ti-4Al-2V (industrial designation PT3V) are investigated. The alloy was produced by equal-channel angular pressing (ECAP). It is demonstrated that the enhanced thermal stability of the SMC alloy structure is associated with a change in the concentration of aluminum at the grain boundaries during ECAP.

Spark Plasma Sintering studies of the high-speed consolidation of pure tungsten carbide WC nanopowders have been carried out. The influence of the initial size of the WC nanoparticles and modes of their receiption the density, structural parameters, and mechanical properties of tungsten carbide are studied. Samples of high-density nanostructured tungsten carbide with high hardness (up to 31–34 GPa) and an increased crack resistance (4.3–5.2 MPa m1/2) are obtained. It is found that the effect of accelerating tungsten carbide nanopowder sintering under conditions of high-speed heating is associated with the acceleration of diffusion along grain boundaries in the sintered material. It is shown that the nonmonotonic dependence of the optimal sintering temperature on the initial grain size is caused by a change in grain-boundary diffusion coefficient in conditions of abnormal grain growth. It is found that the size of abnormally large grains in spark plasma sintering depends on the volume fraction of particles of the nonstoichiometric phase.