High Level Of Mechanical Properties Research Articles

Oxidation resistance and mechanical properties of Zr–Si–N coatings with cyclic gradient concentration

Zr–Si–N coatings with cyclic gradient concentration were fabricated using reactive direct current magnetron cosputtering. The low-Si-content coatings, Zr60N40 and Zr58Si2N40, exhibited a face-centered cubic (f.c.c.) structure, accompanied with a nanohardness of 21.0–23.6GPa and a Young's modulus of 248–267GPa, whereas the medium-Si-content coatings, Zr54Si6N40 and Zr52Si8N40, exhibited a mixture of f.c.c. and near-amorphous structures, accompanied with a nanohardness of 19.7–18.4GPa and a Young's modulus of 204–207GPa. When the Si content ranged from 14 to 19at.%, the structures of Zr–Si–N coatings were X-ray amorphous; those coatings exhibited lower nanohardness levels of 13.7–10.3GPa and Young's modulus values of 196–148GPa. The high-Si-content coatings, Zr28Si24N48 and Zr22Si30N48, exhibited an amorphous structure, accompanied with a nanohardness of 13.7–16.2GPa and a Young's modulus of 196–217GPa, which were higher than those of the coatings with a Si content of 14–19at.%. Coatings formed by adding Si into the Zr–N matrix and performing annealing at 600°C in a 1% O2–99% Ar atmosphere showed notably high oxidation resistance because Si–Zr–O oxide scales formed on the surfaces. The mechanical properties of crystalline Zr–Si–N coatings declined after annealing, whereas near-amorphous Zr–Si–N coatings retained high levels of mechanical properties after annealing.

MICROSTRUCTURE AND PROPERTIES OF PARTS PRODUCED BY DIRECT LASER DEPOSITION OF 316L STEEL POWDER

Direct laser deposition of metal powders is one of the additive methods of functional product manufacturing. It consists in metallic powder melting with laser beams in the inert gas atmosphere. Main process parameters include laser beam power, speed, scanning strategy and powder consumption. Each of the parameters is selected depending on the alloy type that jointly affects the structure and defect formation in products. The present paper shows that the experimental rectangular specimens of powder austenitic steel 316L were obtained by direct laser deposition. The microstructure and fractures of samples were studied using scanning electron microscopy in order to determine the structural features and identify any defects (pores, holes, crystallization cracks and oxide inclusions). Uniaxial tensile tests and hardness tests were carried out. The effect of laser beam scanning strategy on the microstructure and properties of samples when melting was analyzed It was observed that a dispersed structure with an average crystallite size of 1,3–1,9 μm is formed at 250 W laser power and 16 mm/s scanning speed that causes a high level of mechanical properties of experimental samples. It was shown that tensile strength at the lengthwise strategy (along the largest sample size) was up to 730 MPa with an elongation rate 25 % that exceeded 316L steel mechanical properties by 110 MPa.

Study of the Structure and Properties of Especially Strong Aluminum Alloys of the Al–Zn–Mg–Cu System

Especially strong aluminum alloys of experimental compositions are studied, wt.%: Al – (8.0–9.5) Zn – (1.6–2.2) Mg – (1.2–2.0) Cu – (0.08–0.15) Zr – 0.17 Sc – 0.24 Ag – (0.05–0.07) Ti – (0.03–0.04) Mn – (0.05–0.12) Fe – (0.01–0.02) Si. Heat treatment regimes are selected. The effect of alloying and artificial ageing regimes on the structure and properties of experimental alloys are determined. It is shown that especially strong alloys of the Al–Zn–Mg–Cu system after ageing by a single-stage regime (T1) exhibit maximum strength (σu up to 700 MPa). Two-stage softening regime of type T22 provides a high level of mechanical properties combined with satisfactory corrosion resistance.

ОСОБЕННОСТИ ТЕРМИЧЕСКОЙ ОБРАБОТКИ СТАЛЕЙ ДЛЯ ИЗГОТОВЛЕНИЯ ШТАМПОВ ГОРЯЧЕГО ДЕФОРМИРОВАНИЯ

The authors identified the influence of heat treatment parameters on the structure and properties of the advanced 70H3G2FTR die steel for hot deformation. The optimal heat hardening mode for the hot working hammer die produced from the suggested steel is recommended, which contains spheroidizing annealing at the temperature of 780 °C with the slow furnace cooling up to 550 °С and the following still air cooling up to the normal temperature; hardening at 1000 °С with oil cooling; high-temperature tempering at 550–600 °С with the still air cooling. During the hardening process, the structure of lath martensite with the high density of dislocations and the hardness HRC 57–62 is formed, however, 0.5–0.6 % of carbide phase remains insoluble. It is shown that at the stage of high-temperature tempering at 550–600 °С, the process of hardness stabilizing by special complex carbide and intermetallic compounds inclusions can be observed in 70H3G2FTR steel. The analysis of carbide phase at the tempering shows that the compounds of Ме 7 С 3 and Ме 3 С types are the carbides, which composition changes in the process of thermal influence. So, for example, part of Fe and Cr atoms are replaced with Ti and V atoms in various ratios. The authors simulated the temperature-stress condition of hammer die during thermal treatment. It is shown, that the suggested mode of thermal treatment of 70H3G2FTR steel leads to the production of the dispersed ferrite-cementite structure with the distributed special carbides, high level of mechanical properties, and provides the uniform distribution of temperature fields along the volume of hot deformation stamp and, as a consequence, the insignificant internal residual stresses. At the stage of high-temperature soak, the temperature gradient is minimized and does not exceed 25–30 °С.

Technological Aspects of Returnable Material Introducing within Die Casting Technology

Recent survey in manufacturing of aluminium alloy casts, which are now deeply implemented into fast developing car, shipbuilding and aviation industries, is focused on increasing of utility and quantitative properties of a cast to gain its high levels of mechanical properties at reasonable costs. One way how to minimize manufacturing costs is using returnable material at the manufacturing process. The submitted paper deals with an analysis of influence of the percentage proportion of returnable material in a batch on technological manufacturing of aluminium alloy casts. In the experimental part are described the performed experiments aimed to analyse returnable material impact to cast quality represented by monitored mechanical property – a permanent „s“ deformation.

The Low-Nickel Cryogenic Steel Alloyed by Nitrogen

New low-nickel Cr18Ni5Mn9Mo2N and Cr19Ni6Mn10Mo2N steels can be used up to-170 °C and differs in the highest level of durabilities in the hot-rolled and tempered from austenitic area state that provides its effective application in climatic conditions of the Arctic and Antarctic. Excess of durability over level, characteristic for traditional stainless steel of the Cr18Ni9 type, is provided due to additional solid solution hardening. Alloying with nitrogen to 0,18÷0,22% usual Cr18Ni9 steel has the smaller, but also high level of mechanical properties, differs in smaller thermal and mechanical stability of austenite and can be applied in less rigid on temperature and loadings service conditions. Corrosion resistance of austenitic stable steels free from contaminations is also higher compared to steel with regular cleanliness.

The Role of Preliminary Heat Treatment in the Formation of Ultrafine-Grained Structure in the Implementation of the Combined Process "Rolling - Equal Channel Angular Pressing"

In recent years was developed a number of new methods of processing of metals by pressure aimed at obtaining metal with sub-ultrafine-grained structure, the basic principle of which is the realization in the process of deformation of simple shear scheme. One of those ways is pressing blanks in matrices of different designs, in particular in equal-channel step die. However, this method has a significant disadvantage - it can’t be used for deforming of lengthy billets. Another disadvantage of this method of deformation is that it does not provide the continuity of the pressing process. For removing these shortcomings at the Department "Metal Forming" of Karaganda state industrial University was developed a combined process "Rolling-pressing" using equal channel step matrix with calibrated and smooth rolls. This work investigates the impact of the proposed combined process "rolling-pressing", and also preliminary and final heat treatment during the implementation of this combined process on the evolution of microstructure and mechanical properties of copper alloy. Obtained in the course of these studies, the results indicate that the proposed technology can be recommended for implementation in production to produce blanks of ferrous and non-ferrous metals and alloys with ultrafine-grained structure and high level of mechanical properties.

Microstructure and Property Formation for High-Strength Low-Carbon Steels Microalloyed with Titanium and Molybdenum

Features of microstructure formation for hot-rolled product of low-carbon steels microalloyed with titanium and molybdenum are studied. The possibility is demonstrated of achieving a high level of mechanical properties due to forming a volumetric system of nanosize complex (Ti, Mo)C carbide precipitates during cooling after hot rolling, including during cooling of a wound coil with γ → α transformation, and also as a result of forming a finely dispersed ferrite structure with increased dislocation density. Conformity of the temperature for the end of rolling and strip winding on a coil with a cooling regime in this temperature range, and also an increase in free titanium content in this steel, are desirable.

Super thermoplastic vulcanizates based on carboxylated acrylonitrile butadiene rubber (XNBR) and polyamide (PA12)

Thermoplastic vulcanizates (TPVs) are special classes of thermoplastic elastomers, in which dynamic vulcanization of the rubber phase takes place during melt mixing with a semi-crystalline thermoplastic matrix phase at elevated temperature. TPV is characterized by processing behaviour like thermoplastic at elevated temperature and performance properties of vulcanized rubber at ambient temperature. High performance TPVs or super TPVs are new generation TPVs which exhibit high heat resistance as well as excellent oil resistance property suitable for automotive under-the-hood applications. In the present work, a new super TPV based on carboxylated acrylonitrile butadiene rubber (XNBR) and polyamide (PA12) has been developed. (XNBR:PA12) TPVs of different blend ratios have been prepared by using a fixed concentration of novel cyclic monofunctional peroxide. Final morphology of TPVs varies from either a co-continuous to a dispersed one depending on the blend ratio. TPV of 50:50 XNBR-PA12 shows the highest mechanical properties as well as superior thermal stability among all other TPVs. From differential scanning calorimetric (DSC) study, it can be clearly seen that the glass transition temperature (Tg) of XNBR has shifted to high temperature range in case of all TPVs as compared to that of uncrosslinked blend system. Dynamic mechanical analysis (DMA) also demonstrates that tanδ values of all the TPVs are lower and the storage moduli are higher than the uncrosslinked blend system. Lowest tanδ peak of TPV of 50:50 blend ratio of XNBR:PA12 indicates the highest degree of crosslinking and this is also supported by the swelling studies. The highest level of mechanical properties and superior thermal stability support that phenomenon. Heat aging and oil resistance study have also been carried out in details to understand the performance behaviour of these super TPVs at service condition.

STRUCTURE AND STRENGTH OF LOW-NICKEL NITROGENOUS STAINLESS STEEL IN CAST AND DEFORMED STATE

New low-nickel Cr19Ni6Mn10Mo2N steel has highest durability in the hot-rolled and tempered from austenitic area state that provides its eff ective application in the Arctic and Antarctic climatic conditions. The excess of durability over level, common for traditional stainless steel of the Cr18Ni10 type, is provided due to additional solid solution hardening. The usual Cr18Ni9 steel, alloyed by nitrogen to 0.18 %, has the smaller, but also high level of mechanical properties, diff ers in smaller thermal and mechanical stability of austenite and can be applied in less rigid on temperature and loadings service conditions.

Анализ влияния нового совмещенного процесса «равноканальное угловое прессование-волочение» на микроструктуру и свойства деформируемой медной проволоки

The problem of resource-saving methods of producing materials with properties combining high strength and ductility in conditions of using relatively simple and inexpensive devices that enable to implement the whole bulk of metal and intensive plastic deformation while using the minimal amount of energy and effort is very important. In manufacturing wire from non-ferrous metals and alloys, this problem can be solved by using a combined method of deformation “pressing-drawing“ which has a significant advantage compared with the existing technology of producing copper wire. This method of deformation enables to produce wire with a sub-ultrafine grained structure and a high level of mechanical properties, required dimensions and a cross-sectional shape with a small number of deformation cycles.

Applied Aspects of Low-carbon and Low-alloy Steel Recrystallization

The efficient use of low-carbon and low-alloy structural steels in Russia depends on the degree of structure fineness. The most acceptable method of providing the fine-grain structure is the recrystallization annealing. The main purpose of annealing is to build a uniform structure providing for better workability of steel products and higher level of mechanical properties thereof. It becomes possible as a result of recrystallization in solid state to correct such a significant defect of steel structures as the coarse-grained structure obtained as a result of overheating. The possibilities of passive flux-gate test method have been studied to check shaping the fine-grained structure in the course of recrystallization annealing.

DISPERSION OF QUENCHED LOW-CARBON STEEL BY COLD PLASTIC DEFORMATION WITH FURTHER INTENSIVE HEAT TREATMENT

The evolution of structure and mechanical properties of quenched low-carbon alloyed steel 15Cr3Mn3MoVTi after complex deformation-ther- mal treatment is investigated. It was shown that successive combination of cold radial forging with deformation ratio 60 % and one-time accelerated heating at 900 °C with water quenching provides nanostructured condition of investigated steel with average lateral dimension martensite lath near 80 nm and high level of mechanical properties. Increase accelerated heating temperature or increase number of heating cycles reduces to coarsening of steel structure.

INVESTIGATION OF THE PRECISION OF THE INTERNAL CHANNEL OF HOT-ROLLED PIPES DURING EXPANSION

At present, one of the highly demanded types of metal products is steel pipe for constructional purposes. The most important characteristics are its dimensional accuracy and surface fi nish, high level of mechanical properties and operating characteristics. Particular attention is paid to the precision of the internal channel of pipes, because this parameter determines the reliability and cost-effectiveness of their use. One of the most effective ways to increase the precision of the internal channel is pipe expansion by a mandrel. To investigate the accuracy of pipes a program of fi nite element simulation should be used. This has allowed us to investigate the extrafocal expansion at the inlet and outlet of the deformation zone, the inhomogeneity of deformation and the increasing pipe accuracy. The evaluation of these characteristics is an important factor for developing optimal conditions of deformation and tool design high-precision pipes in order to produce in terms of their inner diameter.

Geopolymer Cements and Their Properties: A Review

Abstract Concrete is the world's most versatile, durable and reliable construction material. Next to water, concrete is the second most used substance on earth and it requires large quantities of Portland cement. The industrial sector is the third largest source of man-made carbon dioxide emissions after the transportation sector as the major generator of carbon dioxide, which pollutes the atmosphere. Ordinary Portland cement (OPC) production produces the largest amount of carbon dioxide amongst all industrial processes. In addition to that a large amount of energy is also consumed for the cement production. The production of OPC not only consumes a huge amount of the natural resources i.e. limestone and fossil fuels but also produces almost 0.9 t of CO2 for 1t of cement clinker production. Thus, the world cement production generates 2.8 billion tons of manmade greenhouse gas annually. Hence, it is inevitable to find an alternative material to the existing most expensive, most resource and energy consuming Portland cement. Geopolymer cements are innovative binders which can be produced by the chemical action of aluminosilicate materials plenty available worldwide. They are rich in silica and alumina reacting with alkaline solution and producing aluminosilicate gel that acts as the binding material for the concrete. Geopolymers are synthesized by polycondensation reaction of geopolymeric precursor and alkali polysilicates. The paper presents data on the important engineering properties of geopolymer cements showing that these cements offer an alternative to, and potential replacement for, OPC. Geopolymer technology also has the potential to reduce global greenhouse emissions caused by OPC production. Due to the high level of mechanical properties of geopolymer cements and their environmentally beneficial technology they appear as a prospective construction material for the future.

Structural Features of Structural Steels Microalloyed with Nitrogen and Vanadium

Results are presented for a study of medium-carbon structural steels for the effect of microalloying with nitrogen, vanadium, and other nitride-forming elements on the microstructure and processes of nitride formation after hardening with tempering and rolling. The level of mechanical properties is compared after different treatment. It is shown that a lower bainite structure forms with high dislocation density after rolling and cooling steel to 550°C. Within ferrite plates there is precipitation of finely dispersed densely located vanadium carbonitride. Strength as a result of good dispersion of the fine lower bainite structure, high dislocation density, and dispersion strengthening with precipitation of nanosize carbonitride phase, provides a high level of mechanical properties after rolling and cooling to 550°C, comparable with the level of properties after hardening and tempering.

Poly(ethylene glycol) diacrylate/hyaluronic acid semi-interpenetrating network compositions for 3-D cell spreading and migration

To serve as artificial matrices for therapeutic cell transplantation, synthetic hydrogels must incorporate mechanisms enabling localized, cell-mediated degradation that allows cell spreading and migration. Previously, we have shown that hybrid semi-interpenetrating polymer networks (semi-IPNs) composed of hydrolytically degradable poly(ethylene glycol) diacrylates (PEGdA), acrylate-PEG-GRGDS and native hyaluronic acid (HA) support increased cell spreading relative to fully synthetic networks that is dependent on cellular hyaluronidase activity. This study systematically investigated the effects of PEGdA/HA semi-IPN network composition on 3-D spreading of encapsulated fibroblasts, the underlying changes in gel structure responsible for this activity, and the ability of optimized gel formulations to support long-term cell survival and migration. Fibroblast spreading exhibited a biphasic response to HA concentration, required a minimum HA molecular weight, decreased with increasing PEGdA concentration and was independent of hydrolytic degradation at early time points. Increased gel turbidity was observed in semi-IPNs, but not in copolymerized hydrogels containing methacrylated HA, which did not support cell spreading. This suggests that there is an underlying mechanism of polymerization-induced phase separation that results in HA-enriched defects within the network structure. PEGdA/HA semi-IPNs were also able to support cell spreading at relatively high levels of mechanical properties (∼10kPa elastic modulus) compared to alternative hybrid hydrogels. In order to support long-term cellular remodeling, the degradation rate of the PEGdA component was optimized by preparing blends of three different PEGdA macromers with varying susceptibility to hydrolytic degradation. Optimized semi-IPN formulations supported long-term survival of encapsulated fibroblasts and sustained migration in a gel-within-gel encapsulation model. These results demonstrate that PEGdA/HA semi-IPNs provide dynamic microenvironments that can support 3-D cell survival, spreading and migration for a variety of cell therapy applications.

The Effect of Induced Vibration on Thermoplastic Composite System

Thermoplastic composite manufacturing is often difficult due to high viscosity of the matrix materials. Coupling a high level of mechanical properties with simple, low-cost processing technique is a difficult subject, but an important task for any state-of-the-art impregnation processes. In this paper, Thermoplastic Prepreg Fabrication Technology is utilized to prepare thermoplastic tapes and the technology's effect on strain energy absorption was investigated. The tape was prepared under three categories: first, with induced vibration and no fiber preheat (NV), second, without vibration and fiber preheat (HN) and last, with both fiber preheat and vibration (HV). For the purpose of comparison, all other variables such as pulling speed, fiber tension, fiber preheat and processing temperature were kept constant. The HV category showed improvement in the strain energy absorption by 10 and 23% when compared to HN and NV, respectively. In addition, HV had better wetting, fiber spread and dispersion. Fiber preheating is important as it worked well with vibration possibly due to good fiber spread on the HV category (widest tape). Also, HV had the least fiber volume fraction as it takes more matrix volume when exiting the die plate.

Effect of Low-Temperature Thermomechanical Treatment on the Structure and Mechanical, Fatigue and Corrosion Characteristics of Sheets from an Alloy of the Al – Mg – Si – Cu – Zn System

The effect of deformation on the structure, strength and fatigue properties, stresses on the surface and sensitivity to intercrystalline corrosion of sheets from alloy 1370 of the Al –Mg – Si – Cu – Zn system with one-side cladding is investigated. Application of deformation to sheets of alloy 1370 between the stages of artificial aging lowers the depth of penetration of ICC (≤ 0.10 mm) and raises the fatigue characteristics (by up to a factor of 2) at a high level of mechanical properties.

New Combined Process “Pressing-drawing” and Impact on Properties of Deformable Aluminum Wire

The aim of this work is to study the influence of the combined process of “pressing-drawing” on the microstructure and mechanical properties of aluminum wire. Analysis of the results of the research has shown that the proposed combined method of deformation “pressing-drawing” has a significant advantage over the existing technology of production of aluminum wire. This method of deformation due to combination of two ways: by severe plastic deformation in equal channel step die and the process of drawing through a drawing die, allows obtaining aluminum wire with ultrafine-grained structure and a high level of mechanical properties, required size and shape of the cross section at a small number of cycles of deformation. Also would like to mention that this method of deformation in implementing it in production does not require significant economic investments, and substantial refitting of existing drawing mills.