High Level Of Mechanical Properties Research Articles

Decomposition features and mechanical properties of aging Ti49Ni51 alloy with shape memory effects subjected to heat treatment

The features of the microstructure of the Ti–51 at.%Ni shape memory alloy have been studied after aging at various temperatures. In combination with studies using optical and electron microscopy and X-ray analysis, mechanical properties were tested for tensile strength at room temperature. It has been established that the aged alloy is distinguished by a high level of mechanical properties (tensile strength up to 1200 MPa with a relative elongation of up to 35 %) due to highly dispersed homogeneous decomposition and the effect of simultaneous hardening and increased plasticity as a result of deformation-induced martensitic transformation.

Термическая стабильность микроструктуры сплава MG-Y-ND в экструдированном состоянии

Introduction. Today, bioresorbable magnesium alloys possessing the required physical, mechanical, corrosion, and biological properties, are promising materials for orthopedic and cardiovascular surgery. The addition of rare earth elements such as yttrium, neodymium, and cerium to magnesium alloys improves its properties. Compared to widely used titanium alloys, magnesium alloys have a number of advantages. Bioresorbable materials slowly dissolve in the body, and recurrent operation to remove the implant is not needed. Biocompatible magnesium alloys have a fairly low elastic modulus (10 to 40 GPa), approaching to that of cortical bone, that reduces the contact stress in the bone-implant system. At the same time, strength properties of magnesium alloys alloyed with rare earth elements do not always meet the requirements for medical applications. Severe plastic deformation, for example, equal channel angular pressing, torsion under quasi-hydrostatic pressure, uniaxial forging, extrusion, is therefore very promising technique to gain the high level of mechanical properties of metals and alloys. Severe plastic deformation of magnesium alloys improves its structural strength by 2.5 times due to the generation of an ultrafine-grained and/or fine-grained structure. The issues related to the study of heat resistance, structure and phase composition of magnesium alloys with appropriate strength are relevant. Purpose of the work is to determine the influence of thermal effects on the microstructure of the extruded Mg-Y-Nd alloy. Methodology. The extruded Mg-2.9Y-1.3Nd alloy (95.0 wt. % Mg, 2.9 wt. % Y, 1.3 wt. % Nd,  0.2 wt. % Fe,  0 wt. % Al) is investigated in this paper. The thermal stability of the alloy microstructure is studied after annealing at 100, 300, 350, 450 and 525 °С in argon for one hour. The microstructure and phase composition are investigated using optical, transmission and scanning electron microscopes and analyzed on an X-ray diffractometer. Results and discussion. The extruded Mg-2.9Y-1.3Nd alloy has the bimodal fine-grained microstructure. It is found that along with the stable α-Mg phase, the alloy structure consists of Mg24Y5 intermetallic particles and -, -, and 1-phase precipitates. Annealing in the temperature range of 100–450 °С for one hour has no effect on the structure of the Mg-2.9Y-1.3Nd alloy, but promotes the growth in the linear dimensions of -, -, and 1-phases precipitates. In the temperature range of 300–450 °С, the morphology of -, ,- and 1-phases changes, while the average grain size of the major -phase remains unchanged. Annealing at 525 °С leads to a notable transformation of the bimodal microstructure of the alloy, which is associated with the intensive growth in the grain size of the -phase, Mg24Y5 particles, and -, -, and 1-phases precipitates. Annealing in the temperature range of 100–450 °C leads to an increase in the linear dimensions of Mg24Y5 particles, -, -, and 1-phases precipitates and bimodal microstructure of the Mg-2.9Y-1.3Nd alloy remains unchanged.

Особливості електронно-променевого зварювання магістральних трубопроводів з титанового сплаву

Titanium alloys have high strength and satisfactory weldability. They are widely used in the production of aircrafts and other structural elements in the modern aerospace industry. However, due to a high requirement for aviation and rocket-space technology, increasing the reliability and durability of responsible purpose remains an urgent issue. In this study, the results of welding tubular billets with an electron beam are presented. The subject of this article is the features of tubular billets made of complex titanium alloy electron beam welding. The purpose of this work is to ensure that welds of tubular work pieces have a high level of mechanical properties, based on the welding modes experimental testing results. To achieve this goal, the following tasks were set up and solved in this work: to investigate the mechanism of pore formation in welded joints; to study the effect of electron beam welding on the properties of the weld; ensure high indicators of physical and welded joints mechanical properties. The following research results were obtained. It was possible to obtain satisfactory characteristics of the welded joint by welding in the lower position on the substrate and in the horizontal position. The use of heat treatment increases the strength of welded joints to the level of the base metal. Welded seams, regardless of the welding method, have a coarse-grained structure with liquefaction heterogeneity, which is manifested in uneven etching of the seam. Conclusions: Various metallurgical aspects of titanium electron beam welding were studied. During electron beam welding of tubular blanks, pores are formed mainly near the fusion zone and in the seam axis. Edge mechanical processing, speed reduction, work piece rotation, and welded metal remelting dramatically reduce the number of pores in seams welded in the lower position. Crater removal with a stationary work piece avoids root defect formation in the area of annular seam closure. The obtained results have scientific and practical value in the welded joints of tubular blanks mechanical properties improvement.

MATHEMATICAL MODELING OF THE HOLLOW PROFILES FORMING PROCESS

Steel alloys containing manganese and boron are increasingly being used in mechanical engineering, including automotive and agricultural sectors. Products of critical application made from such steels, including hollow ones, have a high level of mechanical properties, surface hardness, and wear resistance. These products are obtained by profiling of previously electrically welded round pipes with a hot sheet stamping or pressure treatment (drawing, cold rolling, stamping). Technological parameters of combined processing methods are determined by the results of experimental research, which, due to the complexity and cost of materials, leads to significant expenses. The application of mathematical modeling can reduce the number of experiments and forecast the quality of finished products. The research focuses on investigating the possibility of obtaining square hollow profiles by means of push-pulling through one stand of a pipe welding unit and defining the requirements for geometric parameters of the billet.

Mechanical properties of vinyl ester hybrid composite laminates reinforced with screw pine and glass fiber

<abstract> <p>The screw pine and E-glass fibers were hybridized in the vinyl ester resin matrix to prepare the hybrid composite laminates in the present communication. Hybrid composite laminates at the constant volume fraction of 35.12% has been fabricated using the hot press compression molding in two forms, namely dispersed and skin-core, to evaluate the mechanical properties. Mechanical properties of composite laminates were studied based on the various volume fraction of glass fiber content (0, 3.32, 8.15, 12.44 and 16.53 vol.%). The scanning electron microscopy (HITACHI S-3000N) was used to study the fracture surface of composite laminates. The results of hybrid composite laminates were compared with a neat resin sample and screw pine fiber (35.12 vol.%) alone composite. The results revealed that the mechanical properties of both the type of composite laminates increased as glass fiber addition was increased. The SPF18.59/GF16.53 hybrid composite laminate exhibits the highest level of mechanical properties because of the concentration and higher elongation percentage of glass fibers. Moreover, the skin-core type composites perform better than those of the dispersed type hybrid composites. Because of the stretching nature of screw pine fibers, they elongate when the load is transferred from glass fibers to screw pine fibers, resulting in an increase in mechanical properties. The property values were predicted using a theoretical model, and it was found that the two were in good agreement.</p> </abstract>

Створення та обробки мідних сплавів, легованих хромом, цирконієм та ванадієм

The rapid development of mechanical engineering and electrical engineering requires alloys that have high electrical conductivity and a high level of mechanical properties, including strength at elevated temperatures. Pure and low-alloyed copper are ductile, but low-strength materials, which prevents their application in many areas. The solution of such problem can be in alloying with metals that would increase strength characteristics while maintaining electrical conductivity as much as possible, including at high current and temperature loads. The main alloying elements analyzed in this work as effective strengthening components were Cr, Zr, and V. It is shown that the increase in strength while maintaining electrical conductivity depends to a greater extent on the chromium content, the concentration of which in alloys can reach 5-10 wt. %. It was established that to achieve optimal characteristics of strength and electrical conductivity, the concentration of chromium can be close to 0,1 wt. %, and zirconium - up to 0,2 wt. %. At the same time, both for alloys with a high chromium content and in low-alloyed compositions, the characteristics of strength and electrical conductivity can differ by only 10-20%. In the vast majority of cases, copper alloys with chromium and zirconium undergo a specific, sometimes compositional and multi-stage, deformation treatment, after which a fine crystalline structure with nano-sized allocations of strengthening dispersoid phases can be formed. All considered alloys show similar technological features of obtaining a high level of final properties - homogenization and tempering from temperatures of 900-1000 °С and aging at 500 °С for 2 hours or more. At the same time, the higher the content of chromium and zirconium, the more difficult the deformation and heat treatments will be. Additional microalloying with vanadium in the amount of up to 0.2 wt. % may increase strength without a noticeable decrease in electrical conductivity and without the need for the complication of deformation and heat treatments. Keywords: alloying of copper alloys, Cu-Cr-Zr, Cu-Cr-Zr-V, heat treatment, deformation, electrical conductivity.

Water absorption and mechanical behaviour of green fibres and particles acting as reinforced hybrid composite materials

Abstract This paper highlights the results of an experimental study on the preparation and characterization of Luffa cylindrica fiber (LCF) and groundnut shell particle (GSP) reinforced phenol-formaldehyde (PF) hybrid composites. The amount of LCFs was fixed at 25 wt%, while the amount of groundnut shell particles ranged from 0 to 25 wt%. Observations were made regarding the water absorption and thickness swelling behaviour of prepared hybrid composites. In addition, the mechanical behaviours of hybrid composites have been studied under both dry and wet conditions. In comparison to dry conditions, the mechanical properties of the hybrid composites were lower when they were wet. Hybrid composites comprising 25% Luffa cylindica fibre and 15% groundnut shell particle (25LCF/15GSP) exhibit the highest level of mechanical properties under both conditions. The percentages of water absorption and thickness swelling increase as groundnut shell particles increase. The composite 25LCF/25GSP exhibited the highest percentage of water absorption and thickness swelling. Compared to date palm leaf (DPL)-reinforced composites, 25LCF/15GSP showed more significant mechanical and physical properties. We concluded that the inclusion of groundnut shell particles in LCF/PF composites substantially improved the mechanical properties of the hybrid composite. The range of increment, however, was narrower under moist conditions compared to dry conditions.

Effect of Fe-Bearing Phases on the Mechanical Properties and Fracture Mechanism of Al–2wt.%Cu–1.5wt.%Mn (Mg,Zn) Non-Heat Treatable Sheet Alloy

The effects of Fe-bearing phases on the structure, mechanical properties, and fracture mechanism of a non-heat-treatable model sheet alloy (wt.%: Al–2%Cu–1.5%Mn(-Mg,Zn)), designed for Al20Cu2Mn3 dispersoids, was investigated. This involved a combination of thermodynamic modeling in the Thermo-Calc program and experimental studies of structure and mechanical properties. It has been shown that the addition of 0.5 and 0.4% iron and silicon leads to the formation of eutectic inclusions in the Al15(Mn,Fe)3Si2 phase. In addition to the Fe- bearing inclusions, the formation of the eutectic Al2Cu and Al2CuMg phases can be expected in the as-cast structure of the experimental alloys. Despite their relatively high fraction of eutectic particles, non-homogenized alloy ingots demonstrated sufficiently high deformation processability during the hot (400 °C) and cold rolling, which made it possible to obtain high-quality sheet alloys (with reduction degrees of 80 and 75%, respectively). The results of the tensile tests revealed that, after cold rolling, the addition of 1% Mg significantly increased the tensile and yield strengths, whereas the effect of 1% Zn was negligible. At the same time, the uniform distribution of Fe-bearing phases in the structure of the cold-rolled sheets contributes to the preservation of the dimple mechanism of the fracture toughness. This helps to maintain the same level of ductility for the cold-rolled sheet Fe-containing alloys as for Fe-free alloys. It has been shown, based on the data obtained, that adding Fe, Si, Mg, and Zn to the base Al–2%Cu–1.5%Mn alloy in a total amount of more than 3% makes it possible to retain the ductile fracture patterns of the base alloy and obtain a fairly higher level of mechanical properties. This suggests the fundamental possibility of using a variety of secondary raw materials (containing the main elements present in aluminum alloys of different alloying systems) to prepare a base alloy that does not require homogenization or thermal hardening.

COMPARATIVE ANALYSIS AND SIMULATION OF WELDING MODES DURING THE CONSTRUCTION OF THE MAIN PIPELINE USING AUTOMATED TECHNOLOGIES

In the present work, the technology of laser welding of the circumferential joints of pipes of the main gas pipeline was studied on the basis of the existing certain experience of its application at the facilities of the gas transmission system and an assessment was made of the possibility of using it as an alternative to automatic arc welding during construction and repair and restoration work. An analysis was made of the use of laser radiation for orbital welding of main pipelines, which showed that the use of this technology makes it possible to increase the productivity of the welding process, to obtain more favorable structures in the seam and in the transition zone, and to ensure a high level of mechanical properties and weld density. Temperature and deformation conditions in the zone of the welded joint help to reduce the likelihood of hot and cold cracking.Modeling of a pipeline section with welded joints made by automatic arc welding and laser welding (hereinafter referred to as LS) was carried out. When modeling welded joints, their geometric parameters for the compared welding technologies were taken into account, as well as the area and volume of the deposited metal, which theoretically correspond to natural values. Loads were applied to the pipe section with a welded seam, imitating three types of mechanical tests: tension, compression and bending, which occur in the case of thermal deformations and soil subsidence during pipeline operation.In the course of the study, stresses were determined in the cross section of a welded joint obtained using two welding technologies, which show the level of mechanical properties of the weld. A comparative analysis and evaluation of the operational reliability of the main gas pipeline with welded joints made by modern automated welding technologies has been carried out.

Boric Acid as A Low-Temperature Graphitization Aid and Its Impact on Structure and Properties of Cellulose-Based Carbon Fibers.

In the present paper, a scalable, economically feasible, and continuous process for making cellulose-based carbon fibers (CFs) is described encompassing precursor spinning, precursor additivation, thermal stabilization, and carbonization. By the use of boric acid (BA) as an additive, the main drawback of cellulose-based CFs, i.e., the low carbon yield, is overcome while maintaining a high level of mechanical properties. This is demonstrated by a systematic comparison between CFs obtained from a BA-doped and an un-doped cellulose precursor within a temperature range for carbonization between 1000 and 2000 °C. The changes in chemical composition (via elemental analysis) and physical structure (via X-ray scattering) as well as the mechanical and electrical properties of the resulting CFs were investigated. It turned out that, in contrast to current opinion, the catalytic effect of boron in the formation of graphite-like structures sets in already at 1000 °C. It becomes more and more effective with increasing temperature. The catalytic effect of boron significantly affects crystallite sizes (La, Lc), lattice plane spacings (d002), and orientation of the crystallites. Using BA, the carbon yield increased by 71%, Young's modulus by 27%, and conductivity by 168%, reaching 135,000 S/m. At the same time, a moderate decrease in tensile strength by 25% and an increase in density of 14% are observed.

Комплексне модифікування сплаву AlSi9Cu3(Fe) кобальтом, ванадієм та молібденом

Aluminum casting alloys of the Al-Si and Al-Si-Cu systems are among the most widely used materials for machine building. Their wide use is associated with low cost, high manufacturability, excellent ability for multiple recycling and sufficient level of mechanical properties. Increasing of Al-Si-Cu alloys mechanical characteristics always remains as a relevant task, which is often solved by several components modification. Presented work is dedicated to investigation of Co, V and Mo complex influence on the structural phase state and mechanical properties of the widely used AlSi9Cu3(Fe) alloy. All modifying additives were added in the amount of 0.1-0.2 wt. %. At the same time, their total content did not exceed 0.5 wt. %. It is shown that the complex modification of AlSi9Cu3(Fe) with cobalt and vanadium contributes to a significant grain refinement and increasing strength of the alloy by more than 20% while maintaining plasticity. At the same time, cobalt mainly performs the function of a modifier of eutectic components, and vanadium plays the role of a grain refiner. Simultaneous modification of the alloy with vanadium and molybdenum ensures refining of all structural components and strength elevating. Both components perform the function of nucleation. The simultaneous addition of cobalt and molybdenum shows the effect of cobalt on eutectic components. Molybdenum actually does not have a nucleating effect and is mainly goes to iron-containing phases. As a result, average mechanical properties can be observed. Triple modification makes it possible to obtain maximum refining of all structural-phase components and increase the strength of the alloy. The highest microhardness of such alloys indicates potentially high level of mechanical properties at elevated temperatures. Keywords: cast aluminum alloys, modification, AlSi9Cu3(Fe), structure, phase composition, mechanical properties.

SELECTION OF TECHNOLOGICAL PARAMETERS OF MODES FOR MANUAL ARC WELDING OF SHUT-OFF VALVES MADE OF STEEL ALLOYED WITH 3–4 % NICKEL

Body of ball valves can be manufactured from A350-LF3 steel according to the US standard ASTM A350, alloyed with nickel up to 4 %. This steel has a tendency to harden in the heat affected zone during welding. The results of computer simulation showed that cooling rates during shielded metal arc welding exceed the recommended range. This can lead to the formation of hardening structures, the development of cold cracks and a decrease in the performance properties of welded joints of ball valves made of A350-LF3 steel.
 To prevent the formation of cold cracks, the preheating and concurrent heating temperatures were calculated. According to the results of computer simulation, it was found that pre-heating and concurrent heating provide the cooling rate of heat affected zone in the recommended range.
 The technology has been developed for welding ball valves made of A350-LF3 steel with mounting nozzles. This technology prevents the formation of cold cracks and provides a high level of strength and toughness of welded joints. The high level of mechanical properties of welded joints is confirmed by results of mechanical tests and metallographic studies.

Effect of Rubidium on Solidification Parameters, Structure and Operational Characteristics of Eutectic Al-Si Alloy

Modification of the eutectic silicon in Al–Si alloys causes a structural transformation of the silicon phase from a needle-like to a fine fibrous morphology and is carried out extensively in the industry to improve mechanical properties of the alloys. The theories and mechanisms explaining the eutectic modification in Al–Si alloys are considered. We discuss the mechanism of eutectic rubidium modification in the light of experimental data obtained via quantitative X-ray spectral microanalysis and thermal analysis. X-ray mapping revealed that rubidium, which theoretically satisfies the adsorption mechanisms of silicon modification, had an effect on the silicon growth during solidification. Rubidium was distributed relatively homogeneously in the silicon phase. Microstructural studies have shown that rubidium effectively refines eutectic silicon, changing its morphology. Modification with rubidium extends the solidification range due to a decrease in the solidus temperature. The highest level of mechanical properties of the alloy under study was obtained with rubidium content in the range of 0.007–0.01%. We concluded that rubidium may be used as a modifier in Al-Si eutectic and pre-eutectic alloys. The duration of the modifying effect of rubidium in the Al-12wt%Si alloy melt and porosity in the alloy modified with rubidium were evaluated.

COMPARATIVE STUDY BETWEEN THE CHEMI-THERMO MECHANICAL PULPING FROM EUCALYPTUS SPP., BAMBUSA VULGARIS AND DENDROCALAMUS ASPER

In this study, pulps of the species Bambusa vulgaris and Dendrocalamus asper were produced through the chemi-thermo mechanical pulping process, which had their morphological and mechanical properties compared with industrially produced Eucalyptus spp. pulp. The total yields of the pulping processes were 71.3 and 77.0% for the species Bambusa vulgaris and Dendrocalamus asper, respectively. The higher basic density presented by the biomass of the Dendrocalamus asper species can lead to a high productivity. Both bamboo species led to pulps with higher mechanical properties compared to industrial Eucalyptus spp. pulp. The pulp of Bambusa vulgaris stood out in terms of mechanical properties, reaching a higher level of mechanical properties with less energy spent on refining, being indicated for the production of papers for applications where high tensile index is required. Dendrocalamus asper pulp proved to be more suitable for applications, in which high liquid absorption capacity is required due to its high bulk.

Mechanical properties and electrical conductivity of Al–Y–Sс–Er cold worked alloy

Aluminum alloys alloyed with rare earth and transition metal are promising materials for electric energy transportation due to their high properties of strength, thermal stability, and electrical conductivity. The features of strengthening, their mechanical properties and electrical conductivity of Al–0.2Y–0.2Sc–0.3Er alloy after cold rolling have been established. The alloy as a cast structure is presented by aluminum solid solution (Al) and dispersed eutectics with τ2 (Al75-76Er11-17Y7-14) phase upon complete dissolution of scandium in (Al), and a content of yttrium and erbium at the level of 0.2–0.3 % each. Cold rolling the ingot accelerates strengthening upon annealing at 270 and 300 °C, reducing the time of achieving peak hardness. The maximum strengthening due to precipitation of L12 dispersoid of Al3(Sc,Y,Er) phase with the average particle size up to 10 nm is achieved after 7 h of annealing at 300 °C after cold rolling. This shows the prevailing heterogeneous mechanism of nucleation due to defects accumulated during cold rolling which stimulates strengthening. The eutectic particles are located mainly along the boundaries, elongated in the rolling direction. Irrespective of the mode of sheet fabrication, the alloy demonstrates high thermal stability up to 400 °C. During annealing of the sheets to 450 °C, their non-recrystallized structure is retained. Ingot annealing at t = 300 °C in 7 h and cold rolling with subsequent annealing under the same conditions provide a high level of mechanical properties and electrical conductivity: σ0.2 = 194 MPa, σu = 210 MPa, δ = 12.1 % and IACS – 60,1 %. The alloy has demonstrated high yield stress up to 100 h of annealing at t = 300 °C.

Corrosion-resistant steels based on Fe – ~13 % Cr: Heat treatment, corrosion- and wear resistance. Review

Martensitic stainless steels with 13 % Cr are widely used in many industries due to their high level of mechanical properties and acceptable corrosion resistance. The paper consolidates information about the guaranteed level of properties and the heat treatment conditions necessary for its implementation. The properties after the treatment proposed by the researchers are compared with the known properties for industrial metal. Dependences of hardness of the hardened steels of 13Cr type with 0.20 – 0.5 % C on austenitization temperature and accompanying changes in the structure were analyzed, the temperatures providing maximum hardening and the temperatures at which the steel ceases to harden were identified. Influence of the austenitization duration, heating and cooling rates on the steels properties is described. The review considers mechanical properties and corrosion resistance after quenching, quenching and tempering in relation to the structural-phase states of steels. It is shown in detail how the type of secondary phases during tempering, their quantity and distribution affect the corrosion resistance of steels with 13 % Cr. It increases with an increase in the heating temperature during austenitization and decreases with an increase in tempering temperature due to precipitation of Cr23C6 carbides and depletion of the matrix in chromium to concentrations below 12 %. The tempering temperature of 500 – 550 °C is recognized as the worst: due to the intense precipitation of carbides, the steel is not passivated, the corrosion rate is maximal. For steels of 20Kh13 type, low tempering quenching (for a combination of high strength, good corrosion resistance and satisfactory ductility) or, more often, high tempering at ~(650 – 700) °C (good ductility, satisfactory corrosion resistance) is recommended. For steels of 40Kh13 type, a temperature of ~700 °C is not recommended due to the increased concentration of carbides and insufficient corrosion resistance. Examples are given of increasing the wear resistance of steels of 40Kh13 type due to surface treatments, from nitriding to laser and plasma surface hardening.

Production of a Non-Stoichiometric Nb-Ti HSLA Steel by Thermomechanical Processing on a Steckel Mill

Obtaining high levels of mechanical properties in steels is directly linked to the use of special mechanical forming processes and the addition of alloying elements during their manufacture. This work presents a study of a hot-rolled steel strip produced to achieve a yield strength above 600 MPa, using a niobium microalloyed HSLA steel with non-stoichiometric titanium (titanium/nitrogen ratio above 3.42), and rolled on a Steckel mill. A major challenge imposed by rolling on a Steckel mill is that the process is reversible, resulting in long interpass times, which facilitates recrystallization and grain growth kinetics. Rolling parameters whose aim was to obtain the maximum degree of microstructural refinement were determined by considering microstructural evolution simulations performed in MicroSim-SM® software and studying the alloy through physical simulations to obtain critical temperatures and determine the CCT diagram. Four ranges of coiling temperatures (525–550 °C/550–600 °C/600–650 ° C/650–700 °C) were applied to evaluate their impact on microstructure, precipitation hardening, and mechanical properties, with the results showing a very refined microstructure, with the highest yield strength observed at coiling temperatures of 600–650 °C. This scenario is explained by the maximum precipitation of titanium carbide observed at this temperature, leading to a greater contribution of precipitation hardening provided by the presence of a large volume of small-sized precipitates. This paper shows that the combination of optimized industrial parameters based on metallurgical mechanisms and advanced modeling techniques opens up new possibilities for a robust production of high-strength steels using a Steckel mill. The microstructural base for a stable production of high-strength hot-rolled products relies on a consistent grain size refinement provided mainly by the effect of Nb together with appropriate rolling parameters, and the fine precipitation of TiC during cooling provides the additional increase to reach the requested yield strength values.

The Structure and Mechanical Properties of the Aging Shape-Memory Ti49Ni51 Alloy after Thermomechanical Treatment

The effect of thermomechanical treatment on the structure and phase transitions of the aging shape-memory Ti–51 at % Ni alloy has been studied. Mechanical tensile tests were performed in combina-tion with optical and electron microscopic and X-ray diffraction studies. An ultrafine grained (UFG) struc-ture was created in the alloy by multipass-rolling plastic deformation and further annealing. It was established for the alloy to have a high level of mechanical properties (ultimate tensile strength up to 1550 MPa at a rela-tive elongation of more than 20%) owing to a highly disperse phase of precipitation with the formation of an UFG structure due to recrystallization.

Влияние деформационной обработки на микроструктуру и механические свойства сплава Ti-42Nb-7Zr

Introduction. The interest of modern medical materials science is focused on the development of beta-alloys of ternary systems (TNZ) based on titanium, niobium and zirconium with the low Young’s modulus, which is comparable with the elastic modulus of the bone. A wide application of the above alloys in medicine is limited by its insufficiently high strength properties, such as yield strength, ultimate strength, fatigue strength, fatigue life, etc. The formation of bulk ultrafine-grained structure in the alloys via deformation processing, including severe plastic deformation, ensures a considerable increase in the mechanical properties of alloys without toxic alloying elements. The aim of the work is to analyze the influence of deformation (multipass rolling and abc-pressing in combination with rolling) on the microstructure and mechanical properties of the alloy of the Ti-Nb-Zr system. The research methods. The Ti-42Nb-7Zr alloy cast blanks were made from pure titanium, niobium, and zirconium iodides by arc melting with a tungsten electrode in the protective argon atmosphere. It is shown that the cast blanks obtained have a high degree of uniformity in the distribution of niobium and zirconium alloying elements. To form an ultrafine-grained (UFG) structure, the cast blanks were subjected to deformation according to two schemes: 1) multipass rolling and 2) a combined method of severe plastic deformation, consisting in abc-pressing and subsequent multipass groove rolling. Results and discussion. As a result of deformation processing by rolling, an ultrafine-grained (UFG) structure is formed, which is represented by non-equiaxed -subgrains with cross-sectional dimensions 0.2…0.8 µm and length 0.2…0.7 µm, dispersion strengthened nanosized ω-phase, as well as subgrains of the -phase. Application of combined severe plastic deformation has promoted formation of a more dispersed UFG (+ω)-structure with an average size of structural elements equal to 0.3 μm. The UFG structure formed as a result of two-stage SPD has provided a high level of mechanical properties: yield strength – 480 MPa, ultimate strength – 1.100 MPa, microhardness – 2.800 MPa, with a low modulus of elasticity equal to 36 GPa.

LABORATORY AND OPERATING TESTING OF HIGH-ALLOY STEEL PIPES MADE BY THE LATEST TECHNOLOGIES

The purpose of the research: evaluation of the quality and durability for pipes made of high-alloyed austenitic and ferritic-austenitic steels, which are manufactured at PJSC "CENTRAVIS PRODUCTION UKRAINE" using the latest technologies, by conducting complex laboratory studies and long-term operational tests at chemical industry enterprises. Materials and methods: the research materials were experimental pipes made of high-alloyed austenitic and ferritic-austenitic chromium-nickel-molybdenum steels of the new generation, manufactured using the latest technologies. The microstructure of the pipes was investigated by metallography and electron microscopy using developed and improved methods. Corrosive researches in laboratory terms included a test on firmness against the local types of corrosion inherent in high-alloy steels: intergranular corrosion (IGC), pitting corrosion (PC), corrosion cracking (CC) and sulfide stress corrosion cracking (SSCC). The mechanical properties of the pipes were determined by tensile and impact bending tests. Long-term operational tests of pipes were carried out in conditions of industrial production at chemical industry enterprises in apparatus for the urea and caustic soda production. Research results: A high content of special low-energy grain boundaries in the theory of coincident nodes’ lattices (SG CSL) was established in the structure of pipes manufactured according to the latest technologies (≥ 75 %); high resistance of pipes against various types of the most dangerous local corrosion compared to existing analogues, a high level of mechanical properties, as well as high corrosion resistance during long-term operational tests in environments at chemical industry enterprises. The implementation of the obtained results will contribute to increasing the efficiency of production and operation for highly alloyed steel pipes in demand on the world market and increasing the competitiveness of domestically produced pipes on the European and world markets.