The deformed biomedical Ti-(18-20)Nb-(3-4)Zr-(1-1.2)Si (% wt.) alloys are studied. Their rolling is carried out at 950 degrees & Scy; by means of the air- and water-cooling; the quenching in water and oil with heating up to 1050 degrees & Scy; is also used. As established with the x-ray phase analysis, the hot deformation of Ti-(18-20)Nb-(3-4)Zr-(1-1.2)Si alloys contributes to the 6- solid-solution heterogeneity into 6 1 phase based on Ti-Nb and 6 2 phase based on Zr-Ti, as a result of which a final dispersed nonequilibrium ( alpha '' + alpha ' ) structure is formed after cooling, that reflects the ( 6 1 + 6 2 ) microstructure formed due to the previous decomposition. After deformation with air cooling, the experimental alloys contain the largest amount of alpha ' phase and have high strength and low plasticity. As shown, a rising of the cooling rate and temperature during quenching leads to the predominance of the orthorhombic alpha '' phase, while the strength of the alloys decreases with a significant increase in plasticity. In the process of deformation and heat treatment, densely and uniformly distributed disperse silicides are also released in the structure, which contribute to the strengthening. For Ti-(18-20)Nb-(3-4)Zr-(1-1.2)Si alloys, the temperature range & Tcy; = 1040 +/- 20 degrees & Scy; is established, the quenching from which allows to obtain high mechanical properties: cs & vcy; = 1100-1150 & Mcy;P & acy;, cs 0.02 = 800- 850 & Mcy;P & acy;, 8 = 11-11.5%. By deformation and quenching of the experimental alloys, a composite material with alloyed soft matrix strengthened by the uniformly distributed dispersed hard particles of silicides is fabricated.

The paper analyses the hardening of binary and multicomponent solid solutions (including high entropy alloys (HEAs)); addresses the notion of a compositional-cluster structure of binary solid solutions with unlimited solubility to propose an equation describing the concentration dependence of the critical shear stress; presents findings from a comparative analysis of the temperature dependences for critical shear stress (yield stress) for a series of binary and multicomponent solid solutions and pure metals with b .c .c . and f .c .c . lattices; considers potential mechanisms, which lead to a 'plateau' on the temperature dependence of critical shear stress for binary and multicomponent solid solutions and for pure metals; discusses the specifics of a thermal hardening of HEAs and proposes a relatively simple equation for assessing their athermal hardening; and addresses the capabilities of using the x-ray diffraction to determine the root mean square displacements of atoms from ideal positions at crystal lattice sites, root U-2, and crystal lattice microdistortions, epsilon, in multicomponent solid solutions.

The tribological properties of heterogeneous Ti–Si–Zr titanium alloys with an e(β-Ti + (Ti, Zr)2Si) eutectic were studied in different friction conditions. Tribological tests were performed with two methods. The samples were subjected to shaft–bush (counterface–material) tests by dry friction against ShKh15 steel employing an M-22M machine at a load of 20 N and a sliding speed of 1–6 m/sec with one method. The other method involved quasistatic and dynamic sphere–plane tests with an effective load of 30 N employing a computer-assisted tribology system. The indenter materials were ShKh15 steel and Si3N4 ceramics. The tests were performed at a sliding speed of approximately 0.0147 m/sec in water. The linear and weight wear rate for the cast Ti–10Si–10Zr–1Sn sample with a superfine eutectic structure determined with the first method at the greatest test speed (6 m/sec) was found to be 1.4 times higher than that of the Ti–9Si–7.6Zr alloy. The Ti–10Si–10Zr– 1Sn alloy showed the lowest wear resistance under quasistatic and dynamic loads with the second method, regardless of the indenter material (ShKh15 or Si3N4). Contrastingly to the previous data for cast irons and steels, the eutectic Ti–Si–Zr titanium alloys for the first time showed smaller wear under dynamic loading than under quasistatic loading. Thermomechanical treatment of the hypoeutectic Ti–9Si–7.6Zr alloy was established to increase its wear resistance by more than 1.6 times.

The Ti-(18-20)Nb-(1-1.2)Si alloys are obtained by electron-beam melting; the sizes of the ingots are as follow: d = 60 mm, l = 650 mm. As shown, the applied smelting method provides a more stable phase composition of alpha + beta + (Ti, Nb)(3)Si in the cast alloys. Hot deformation is carried out at & Tcy; congruent to 1000 degrees & Scy; by means of the rotary forging up to d = 20 mm, followed by thermomechanical treatment (TMT - screw rolling with water cooling) up to d = 12 mm; quenching in water is carried out at 1050 degrees & Scy; with a holding time of 30 min. The structure after deformation is non-equilibrium, consisting of the alpha ( alpha ' )-phase, the residual metastable beta- phase, a small amount of large (Ti, Nb)( 3) Si silicides mainly on the boundaries of the primary beta- grains, as well as dispersed silicides on structural defects, that causes the high strength sigma(B) = 1155 MPa, but low plasticity delta = 3.5 %. During the quenching of the deformed Ti-(18-20)Nb-(1-1.2)Si alloys at 1050 degrees & Scy;, the orthorhombic alpha ''- phase is formed, and the amount of silicides increases. Herewith, the strength is slightly reduced to sigma(B) = 1135 MPa with significant increase in plasticity 8 = 9 %. Two-stage deformation including TMT with final quenching in water at 1050 degrees & Scy; causes the release of a larger amount of dispersed silicides and, as a result, the formation of the alpha ''- phase depleted with alloying elements and the residual beta- phase. The resulting structure provides a better combination of mechanical properties (sigma(B) = 1165 MPa, delta = 12.5 % ) due to dispersion strengthening with silicides and increased plasticity of the solid solution. For deformed experimental Ti-(18-20)Nb-(1-1.2)Si alloys, the quenching temperature & Tcy; = 1080 +/- 10 degrees & Scy; is also determined that allows obtaining the maximum strength sigma(B) = 1190 MPa, while maintaining plasticity at the level of 8 = 9.5 %.

За клініко-рентгенологічними дослідженнями представленізразки імплантів із кальцій-фосфатної кераміки, які повною міроювиконують остеокондуктивну функцію. Однак у випадку щільногоїх контакту з краями кісткового дефекту (дослідна група) первинназапально-резорбтивна стадія репаративного остеогенезу виявиласябільш інтенсивною і подовженою у часі з вираженими явищами остеорезорбції материнської кістки і об’ємної періостальної реакціїяк компенсаторного механізму. При цьому остеоїдне формуванняутворюється навколо імпланта, тимчасом контрольні імпланти частково резорбуються і заміщуються остеоїдною тканиною. Як наслідок, макроморфологічно дослідні імпланти у компактній кістцівізуалізуються до 42-ї доби, у губчастій – до 30-ї доби, тимчасомконтрольні імпланти покриваються кістковим регенератом уже на14-ту добу, що свідчить в останньому випадку про наявність остеоінтеграційних процесів. Гістологічна картина у разі досліднихімплантів підтверджує подовження запально-резорбтивної стадіїіз формуванням навколо них хрящово-кісткового регенерату, тобто щільне розміщення імплантів зумовлює біомеханічний тиск настінки кісткового дефекту з розвитком у них реакції, насамперед настороннє тіло.Вивчення впливу на репаративний остеогенез остеоінтеграційних властивостей розроблених нових індивідуальних та стандартнихза розміром імплантатів з біоактивної кераміки за клініко-рентгенологічного, макроморфологічного та гістоморфологічного обґрунтування є актуальним, оскільки дає змогу оцінити їх переваги щодоконсолідації складних дефектних переломів трубчастих кісток тазменшити частоту їх ускладнень у тварин.

The effect of temperature and content of the main alpha-stabilizers of the structure on the elasticity module and the cyclic strength of heat-resistant titanium alloys are investigated. The alloys are obtained in the electron-beam foundry based on the vacuum induction furnace and are cleaned at alpha - beta transformations. The total degree of deformation of the material is of 94-96%. To compare the results with known data, known heat-resistant titanium alloy & Vcy;& Tcy;25 & Ucy; and a high-strength alloy of & Vcy;& Tcy;6 are investigated. The module of elasticity is determined at longitudinal and bending resonant vibrations in the temperature range from 20 to 820 degrees C, and the curves of multicycle fatigue at bending are plotted at temperatures of 20 and 650 degrees C at a load frequency of about 2 kHz. It is assumed that the physical meanings of the interrelated characteristics of cyclic strength and elasticity are different and, therefore, require separate considerations depending on the temperature and the composition of the main alloying chemical elements. We compare the temperature dependences of elasticity and the dependences of the modulus of elasticity on the weight content of aluminium and on the aluminium equivalent with similar dependences for the endurance limit. The correlation between the indicators and the slopes of the known temperature dependences of the modulus of elasticity and the endurance limit is revealed. Based on this, approximate convex dependences of the endurance limit on temperature are carried out. This makes it possible to compare known and obtained results for fatigue of heat-resistant titanium alloys. As shown, at a temperature of 600 degrees C, the data for the experimental alloy 2 & Tcy;85-3 with a high content of silicon coincide with the values of multicycle fatigue for the known alloy & Vcy;& Tcy;41. As established, the dependence of the endurance limit on the aluminium equivalent at 20 degrees & Scy; is more accurate in comparison with these dependences on aluminium.

The heat-resistant Ti–Al–Zr–Si alloys (base Ti–(6–7)Al–(2–3) Zr–(1–1.5)Si and additionally alloyed Ti–(6–7)Al–(3–5)Zr–(1–1.5)Si–(2–4)Sn), obtained by electron beam smelting were studied. Deformation was carried out in the β- or upper part of the (α+β)-area by means of forging and rolling into a strip. The base alloy was subjected to rolling in the upper part of the α+β-area, and the fine-grained uniform structure with a grain size of 10–20 μm was obtained. Internal stresses and defective substructure of the deformed alloy intensify the decomposition of the solid solution and promote the formation of evenly distributed dispersed silicides, which allows obtaining high strength and heat resistance characteristics. Tensile tests at 20; 650 and 700°C of the Ti–(6–7)Al–(2–3)Zr–(1–1.5)Si alloy samples after deformation and annealing also showed a rather high level of the tensile strength and yield strength. After 20 h exposure at the operating temperature of 700°C, the structure becomes more equilibrium, due to which the strength of the deformed alloy decreases, and the relative elongation increases. Additional alloying of the base alloy with zirconium and tin slightly increases plasticity and decreases heat-resistant properties.

The mechanical and tribological properties of cast monocarbides and multicomponent high-entropy carbides produced by vacuum arc melting using starting monocarbide powders were examined. The cast monocarbides demonstrated a hardness of 20–30 GPa and an elastic modulus of 400–600 GPa. Among the studied monocarbides, ZrC showed the highest hardness (29–32 GPa), while MoC exhibited the lowest hardness (16–18 GPa). The friction coefficient for monocarbides was determined by pin-on-disk testing with diamond in dry friction conditions and in the presence of water. The friction coefficient was found to increase for WC and TiC carbides and decrease for MoC in the presence of water. Based on the studies of monocarbides, cast single-phase multicomponent high-entropy carbides with a NaCl-type cubic lattice and a homogeneous microstructure without any phase separation by chemical composition were developed and produced. The hardness of the cast multicomponent high-entropy carbides was determined, and their normalized hardness was calculated. The high-entropy carbides exhibited higher hardness (33–40 GPa) and normalized hardness (0.072–0.105) but a slightly lower elastic modulus than the monocarbides. The elastic modulus and lattice parameter were theoretically calculated, and the relationship between the size mismatch and hardness of the cast multicomponent high-entropy carbides was shown. The friction coefficient of the multicomponent high-entropy carbides determined by tribological tests was lower than that of the monocarbides both in dry friction conditions and in the presence of water. The friction coefficient was not either found to be dependent on hardness or elastic modulus.

One of the most interesting results obtained in the study of mechanical properties of binary and multicomponent solid solutions (high-entropy alloys, HEAs) is the presence of long athermic hardening, which causes the appearance of a characteristic 'plateau' on the curve of temperature dependence of critical shear stress t( cr )( T ) (or yield strength sigma( 0.2) ( T )) at temperatures above 0.2-0.35 T (m) . From the point of view of creation of the new materials, that are able to withstand mechanical loads at high temperatures, determining mechanisms for the appearance of such a 'plateau' is extremely actual. In the presented work the existing representation about the features of the temperature dependence of the critical shear stress in binary and multicomponent solid solutions are considered in comparison with pure metals. A new approach for determining the nature of athermal 'plateaus' on the curves of temperature dependences of the critical shear stress t (cr) ( T ) is proposed. As shown, the existence of a 'plateau' in the t (cr) ( T ) dependence in solid solutions and in pure metals at the indicated temperatures is, in fact, anomalous, since with an increase in temperature there is a noticeable decrease in their Young's modulus, which, respectively, should also lead to a decrease in the critical shear stress t (cr) . The authors' analysis indicates that the factor that compensates for the expected decrease in t (cr) associated with a decrease in the elastic modulus in pure metals is an increase in the mean square displacements of atoms from ideal positions in the crystal lattice as a result of a linear increase in dynamic distortions of the crystal lattice with increasing temperature. In multicomponent solid solutions, in addition to an increase in the mean square displacements of atoms, the dependence t (cr) ( T ) in the temperature range where a 'plateau' is observed, effects similar to dynamic deformation aging, which are accompanied by unequal mobility of atoms of different elements, can also affect. The results obtained can be used to select the elemental composition of multicomponent heat-resistant alloys, which will be competitive in comparison with the known traditional alloys.

This work presents a magnetron sputtering system with a cylindrical magnetron to can be used for protective coatings in the internal surface of pipes.The main advantage of the system is to operate in both constant and pulse current mode, to perform the preliminary surface cleaning and to form a single-layer or multi-layer coating in one technological cycle.The tantalum and chromium coatings obtained using the systems with the cylindrical magnetron have high physical and mechanical properties.

We study the influence of electron concentration, lattice distortion, and phase ratio on the hardness, elasticity modulus, and normalized hardness of high-entropy two-phase alloys. It is shown that the fractions of phases depend on the concentrations of electrons. A sharp increase in the FCC phase is observed for electronic concentrations higher than 8 el/at. For high-entropy two-phase alloys, we establish a linear dependence of the normalized hardness on the dimensional mismatch. The values of normalized hardness increase from 0.025 to 0.043 as the level of distortion increases from 2.3 to 4.3%.

We study the high-temperature (650°С) creep resistance of prismatic specimens of the known VT25U alloy and experimental ZhT19 alloy of the Ti–Al–Si–X system (X = Zr, Mo, Nb, Sn) in short-term (for 3 h) bending tests. We propose the corresponding characteristics of creep resistance of the materials according to which the ZhT19 alloy is better than the VT25U alloy.

We study the biomedical Ti-18Nb-4Zr-x Si cast alloys with a silicon content of 0.5-1.5 wt.%. Quenching in water was carried out within the temperature range 900-1200 degrees? with durations of holding equal to 5 min and 1 h. It is discovered that the procedure of heating of these alloys to the temperatures of quenching leads to the decay of nonequilibrium phases, and the silicon content is redistributed between the phases in a solid solution and silicides. Since almost all silicon is bound with zirconium and titanium and form silicides, the hardness of the Ti-18Nb-4Zr-x Si alloys mainly depends on the amount of silicides and constitutes 26-28 HRC. Moreover, its maximum values are reached for the alloys with eutectoid compositions containing 0.8-1.2 wt.% Si characterized by the most intense release of finely divided silicides. The increase in the silicon content of the hypereutectoid alloys leads to an increase in the sizes of silicides, as well as to the formation of larger amounts of the beta-phase in the as-cast Ti-18Nb-4Zr-x Si alloys, and as a result, their hardness noticeably decreases. For low quenching temperatures (within the range 900-1000 degrees C), the complete eutectoid destruction accompanied by the formation of relatively large stable (Ti, Zr)3Si silicides leads to a decrease in hardness < 25 HRC. In the course of quenching of the as-cast Ti-18Nb-4Zr-x Si alloys at temperatures >= 1100 degrees C, we observe the formation of more finely divided silicides, which increases the level of hardness of the eutectoid alloys up to 38-39 HRC. The observed changes in the parameters of the alpha ''-phase demonstrate that, as a result of partial dissolution of silicides in the course of quenching at 1200 degrees C, silicon passes into a solid solution and the amount of large silicides on the grain boundaries increases. Therefore, the level of hardness of the analyzed quenched alloys decreases.

The influence of alloying elements and heat treatment on the structure, phase composition and hardness in two series of cast alloys of the Ti-Nb-Si system with a silicon content of 1 and 1.2% wt. and different niobium content from 10 to 18% wt. is studied. As shown, in as-cast alloys of this composition the niobium content in some areas varies in a fairly wide range because of the liquation, respectively, a heterogeneous and nonequilibrium structure is formed, which consists of metastable phases: alpha ', alpha '', 6, dispersed (Ti, Nb) 5 Si 3 and (Ti, Nb) 3 Si silicides. The maximum hardness of the experimental as-cast alloys coincides with the highest content of alpha ' or alpha '' phases and is due to both the doping of the solid solution of these phases and the presence of dispersed silicides in them. As found, increasing the niobium content to 18% wt. in as-cast alloys Ti- x Nb-(1-1.2)Si leads to a decrease in the solubility of silicon in the alpha '' phase and additional precipitation of silicides, as well as an increase in the amount of 6 phase, and, consequently, reduced hardness. Heating and holding of as-cast alloys on heat treatment brings them to a more equilibrium state, which is preserved at low cooling rates. Dispersed metastable (Ti, Nb) 5 Si 3 silicides dissolve, the existing stable (Ti, Nb) 3 Si silicides grow, and new ones are formed, thus increasing their number. That reduces the hardness compared to the as-cast state. It is found that dispersed, newly formed by cooling silicides do not contain niobium and the last one dissolves in silicides during their growth, so large silicides have a composition of (Ti, Nb) 3 Si. As shown, the transition from alpha ' to alpha '' structure in the experimental alloys depends not only on alloying but also on the cooling rate. As the cooling rate increases, the alpha '' phase of different degree of doping is formed, and its orthorhombicity is 0.99-0.96 depending on the niobium content.

The (DD) method was used to model the formation of the plastic zone of the top of the cracks in polycrystalline molybdenum. Special attention was paid to take into account the interaction of dislocations in the plastic zone with grain boundaries. Structural sensitivity of fracture toughness was analyzed under brittle-ductile condition. Simulations were performed for a range of grain sizes from 400 to 100 μm, at which a sudden increase in fracture toughness with a decrease of grain size was experimentally shown. We calculated the value of K1c taking into account the shielding action of dislocations. The position of all dislocations in the plastic zone at fracture moment was calculated. Based on these data, we obtained the dependences of dislocation density on the distance from the crack tip thereby confirming significant influence of the grain boundaries on plastic zone formation. At large grain sizes, when the plastic zone does not touch the boundary, the distribution of dislocations remained unchanged. As grains reduce their size to size of the plastic zone, they start formating a dislocation pile – up near the boundaries. Dislocations on plastic zone move slightly toward the crack tip, but the density of dislocations in the middle of the grain remains unchanged, and fracture toughness remains almost unchanged. Further reduction of the grain size leads to the Frank-Reed source activation on the grain boundary Forming dislocation pile-up of the neighbor grains. Its stress concentration acts on dislocations of the first grain and causes redistribution of plastic zone dislocations. If the reduction in grain size is not enough to form a strong pile-up, density of dislocations on plastic zone increases slightly and crack resistance increases a few percent. Further reduction of grains promotes strong pile-up, dislocations move to crack tip, and its density on plastic zone increases. Crack is shielded and fracture toughness increases sharply. The calculation showed that the fracture toughness jump is observed at grain sizes of 100—150 μm, in good agreement with the experiment. Keywords: dislocation dynamics simulation, molybdenum, fracture toughness, grain size, plastic zone, brittle-ductile transition.

Проведено дослідження литих стопів Ti-18Nb-хSi з вмістом кремнію від 0,6 до 1,2% ваг.Вивчали утворення силіцидів за різних умов термообробки (температури і витримки), їхній розподіл, динаміку росту та розчинення, а також вплив на твердість і біологічні властивості.Найбільше виділення силіцидів (Ti, Nb) 3 Si відбувається в результаті евтектоїдного розпаду твердого розчину за 800-900°С.У процесі гартування в інтервалі температур ≤ 1000°С переважно на межі зерен і дефектах структури виділяються силіцидні частинки з розмірами > 0,05 мкм, які не впливають на рух дислокацій у випадку пластичної деформації.Тому за даних температур стопи не зміцнюються, їхня твердість є досить низькою.Витримка призводить до зростання розмірів силіцидів і

Complex comminuted fractures are accompanied by development of bone defects and loss of reparative potential of the bone tissue in the region of the trauma. This brings the necessity of using implants with optimum osteoconductive and osteointegration properties. The objective of the study was determining the condition of biochemical bone markers and peculiarities of histomorphological changes under the influence of ceramic hydroxyapatite (HA) implants with various physical-chemical properties in the conditions of diaphyseal bone defects in rabbits. We composed control and experimental groups of rabbits with 10 individuals in each with diaphyseal bone defects (3 mm) of the radial bones formed under general anesthesia. In one experimental group, they were filled with granules of hydroxyapatite with α-tricalcium phosphate, and in the second group – with β-tricalcium phosphate, alloyed with Si. In the control rabbits, the defects healed under a blood clot. Blood was analyzed on the 3rd, 7th, 14th, 21st and 42nd days, and as reference we used biochemical parameters of blood of clinically healthy rabbits (n = 10). Bone biopsied materials were taken on days 21–42 under general anesthesia. When using hydroxyapatite with β-tricalcium phosphate, alloyed with Si, we determined early intensification of the levels of nitrogen oxide, angiogenesis and development of bone regenerate in conditions of shortening of inflammatory resorption phase, which was verified according to the level of tartrate-resistant acid phosphatase. According to the level of bone isoenzyme of alkaline phosphatase in the blood serum of animals of the control group, the reparative osteogenesis developed slowly and peaked on day 42, whereas in animals implanted with α-tricalcium phosphate, its development peaked peaked on days 14–42, and when using Si-alloy – on days 7–14. Histomorphologically, on the 21st day, in the case of replacement of bone defect with hydroxyapatite with α-tricalcium phosphate, coarse-fibered type of bone regenerate developed with no dense contact with the elements of the regenerate, while spongy bone trabeculae occurred when hydroxyapatite was applied with β-tricalcium phosphate alloyed with Si, and the control rabbits were observed to be in the stage of cartilaginous callus. On the 42nd day, under the influence of implants of hydroxyapatite with α-tricalcium phosphate, the spongy bone tissue transformed into compact tissue with further mineralization. With implants alloyed with Si, there occurred compact bone tissue, and bone regenerates of the control animals were regions of coarse-fibered and spongy bone tissue without dense contact with the parent bone. This study revealed that hydroxyapatite with β-tricalcium phosphate alloyed with Si had notable osteoinductive and osteointegrating properties, as indicated by early angiogenesis and osteoblast reaction, positive dynamics of the marker biochemical parameters with faster and better development of bone regenerate as spongy bone trabeculae.

Проведено дослідження литих загартованих стопів Ti-18Nb-хZr-1Si з вмістом цирконію від 2 до 8% ваг.Вивчався вплив Цирконію і температури гартування на структуру та твердість.Введення Цирконію має модифікуючий вплив на структуру литих стопів: із збільшенням його вмісту спостерігається зниження лікваційної неоднорідності та зменшення величини зерна.Показано, що у стопах Ti-18Nb-хZr-1Si (х = 2-8%) при гартуванні в залежності від температури витримки утворюється структура різної морфології та дисперсності.У стопі з низьким вмістом Цирконію ≤ 2% ваг.формується крупнопластинчаста α″-фаза, близька до мартенситу в стопі Ti-18Nb-1Si, в той час як більший вміст Zr сприяє переходу до дисперсної тонкої пластинчастої чи голчастої форми мартенситу.За даними рентґенофазового та мікрорентґеноспектрального аналізу у стопах присутні силіциди (Ti, Zr) 3 Si та (Ti, Zr) 5 Si 3 , кількість яких також залежить від вмісту Цирконію і температури гартування.Максимальна твердість у стопах Ti-18Nb-хZr-1Si досягається при вмісті Zr ≅4-6% ваг.

We study new biomedical alloys of the Ti–18Nb– x Si system with 0.6–1.2 wt.% Si both in the as-cast state and quenched in water after holding at temperatures from 800 to 1200°С. It is shown that their solid-solution hardening within certain temperature ranges is supplemented by dispersion hardening with silicides. Rapid cooling after melting promotes the formation of nonequilibrium partially quenched structures with dispersed secondary silicides and high hardness. Quenching at lower temperatures (800–1000°С) leads to an increase in the number and sizes of silicide precipitates and to the depletion of the solid solution of silicon as a result of which the level of hardness decreases. For high quenching temperatures (> 1100°С), the silicides are practically dissolved and the level of hardness also decreases. The temperature range 1050–1150°С proves to be optimal for the purposes of quenching of biocompatible alloys of the Ti–18Nb– x Si system.

The influence of grain size on the physical yield strength of the polycrystal is considered by the method of cellular automata. The physical yield strength of the polycrystal in this model is defined as the stress at which, the plastic deformation covers the entire cross section of the sample from one edge to another. Three mechanisms of plastic deformation are considered. The first one is an initiation of plastic flow from grain to grain by dislocation pile-ups. The second one is plastic flow in different grains independently of each other under the action of external stress and the third one is intergranular slippage. Computer simulations have shown that at large grain sizes (d > 200 nm) deformation propagates from grain to grain by initiating dislocations pile-ups, since in this case pile-ups are quite powerful and have a large effect on neighboring grains. At average values of grain size (20 nm <d <200 nm) plastic deformation occurs in the grains independently of each other, and the external strain give a major influence on plastic deformation. With further reduction of the grain sizes (d <20 nm) the main mechanism of deformation is intergranular slippage. because in grains of this size are quite large image stresses that do not allow large dislocation clusters. In small grains the image forces are quite large to prevent large dislocation pile-ups formation, but the mass and volume of grain are quite small to turn or slip its under the action of external stresses. In accordance with these mechanisms, on the calculated dependence of the physical yield strength vs grain size, there are three areas with different angles of inclination in logarithmic coordinates. Keywords: yield point, grain size, Hall―Petch low.