High-speed Heating Research Articles

Microstructure and micro-hardness behavior of Ti–Y2O3 –Al–Si composite coatings prepared in electron-plasma alloying

The paper investigates micro-hardness behavior, element and phase composition of Al–11%Si compound subjected to electron-plasma alloying (EPA). Essentially, EPA is an electrical explosion of a Ti conductor and a weighted Y2O3 powder sample with further high-speed heating created by an intense pulse electron beam. The work has established a considerable increase in micro-hardness in surface layers of the material. A penetration depth of alloying elements, being a thickness characteristic of the modified layer, is reported to be ˜ 170 μm. A maximal micro-hardness (155 ± 15.5 HV) is detected in a layer to be as close as possible (5 μm) to the surface of modification. Micro-hardness drops gradually at a depth of 110 μm, reaching its initial value 85.9 ± 8 HV at a depth of 170 μm. The research data collected by the methods of X-ray microanalysis and transmission electron diffraction microscopy demonstrate that the structure of EPA-treated composite 5 μm below the surface comprises nano-dimensional (1–100 nm) crystallites composed mainly of aluminum. The study has revealed that in some crystallites and their joining points there are inclusions formed by particles of Ti and Y aluminides (Al3Ti and Y3Al2) and Ti silicides (TiSi2). The structure of alloy ≈70 μm below the treated surface is made of high-speed crystallization cells ranging 0.5 μm–0.6 μm. The crystallization cells are shown to be formed by a solid Al-based solution and surrounded by second phase layers containing Si and Cu2.7Fe6.3Si; cross dimensions of which vary 50–70 nm. A comparison of micro-hardness behavior and concentration of alloying elements in the surface layer of the composite has highlighted a boost of micro-hardness caused by Ti and Y in the modified layer, and multiphase sub-micro-and nano-dimensional structure made of crystallites with dimensions within a range of several units to hundreds of nanometers.

Thermo-mechanical behaviour of granite during high-speed heating

Fire accident is a common and serious damage phenomenon affecting tunnels, historical sites, buildings, monuments, etc. However, the understanding of the thermo-mechanical behaviour of rocks during fire and the corresponding damage on the rocks is still limited. In this study, the thermo-mechanical behaviour of Eibenstock granite under the temperature of 400 °C and 800 °C was studied applying heating rates of 5 °C/min, 200 °C/min, 300 °C/min, and according to ISO 834 standard fire curve. A supersonic frequency induction heating system was used to conduct the required heating scenarios and to perform uniaxial compression tests under the desired temperatures. A threshold modulus Ec obtained from dividing peak axial stress by the peak axial strain is defined to characterize the stiffness of the sample at various temperatures. Both tangent Young's modulus and threshold modulus are greatly influenced by maximum temperature, while the influence of heating rate is relatively small. The maximum temperature has the dominant impact on the uniaxial strength of granite sample, while the influence of heating rates is again negligible. The peak axial strain increased obviously with rising temperature. It first increases at 200 °C/min heating rate and then reduces slightly in scenarios with heating rate of 300 °C/min or heating according to ISO 834. The observed failure modes after uniaxial compression tests are influenced by peak temperature and heating rates. The granite specimen can be crushed in the shape of blocks, fragments or powder. The deduced friction angle for various heating scenarios is more or less consistent, while the cohesion shows a strong temperature-dependent characteristic. Although the cooling process can lead to an increase in crack density, UCS, peak axial strain and cohesion are enhanced at lower temperatures. The presented results help to understand the damage mechanisms of granite caused by fire, and can be used to develop guidelines for repair and maintenance as well as assessment of risks of tunnels and historical buildings after fire accidents.

Features of shock pressing and electro-impulse heating during consolidation of a powder material

The article discusses the method of high-speed shock consolidation of powder materials. In this method, high-speed heating of the powder is carried out by a high-voltage current pulse, and the mechanical force on the powder billet is created by a falling pile driver. A description of the experimental setup that implements this method is given. Energy and kinematics parameters of the shock consolidation process of powder materials are discussed.

DEFORMATION AND FRACTURE OF STRENGTHENED HIGH-CARBON STEEL AFTER TREATMENT IN TEMPERATURE CONDITIONS OF PHASE PRE-TRANSFORMATION AND TRANSFORMATION

Traditional methods of heat treatment are energy-intensive and time-consuming, so the task of increasing their efficiency is very relevant. The process of repeated high-speed heating with short-term aging in the temperature range of polymorphic pre-transformation and transformation from the viewpoint of evolution of structure, properties and character of the fracture of quenched high-carbon steels was investigated. In particular, it was found that high-speed heating (600 – 700 °C/s) and short-term holding (0.5 sec) followed by cooling in salted water (6 °C) leads to the formation of a structure not differing from the structure of low-drawn (200 °C, 2 hours) martensite of traditionally hardened steel with 4 times increase in elongation and 2 times contraction while maintaining strength during the tensile test. Short-term aging of 8 – 15 – 25 seconds with repeated quenching of high-carbon steels from 820 °С in cold salted water (6 °С) leads to formation of the structure of ultra-fine-lamellar, submicroplast, globular perlite. There is a three-dimensional nanostructuring of steel that differs from traditional hardening with high temperature tempering by the structure and properties: magnitude of the applied stresses, both at deformation stages and at fracture (increase in σ by 55 %, in σ0.2 – by 17 %, in ψ – 8 times, in αn – by 80 %). Increase in short-time holding up to 40 – 50 sec, with repeated quenching from 820 °C leads, in contrast to the traditional one, to formation of the structure of ultra-small-malt martensite and to appearance in fracture on the slip planes of the patching structure, resembling a honeycomb in shape. After the low temperature tempering during the tensile test, all stages of deformation are presented. In fracture the crushing of pit structure and the absence of brittle tunnel pits are observed, plasticity is improved (δ ~ 1.5 times, ψ – 3 times) at strength preservation.

The Formation of Composite Coatings with High Hardness with High-Speed Heating

The article dwells on the developed method of induction cladding of refractory compounds based on carbide-boride products (Ti,Cr)B2+W2B5+B4 and TiC+W2B5+FeV using a special charge material in the condition of high-speed heating by high frequency current. It has been established that during induction heating the cladding layers are formed as per the scheme where the refractory component is partially diluted in the bonding molten metal, it does not dissociate and forms strong matrix-reinforced structures with high resistance to wear. The article describes the efficiency of their use in case of abrasive wear.

Investigation and analysis of the possibility of diffusionless phase transformations in the surface layer of a part under the action of grinding temperatures

The possibility of diffusionless phase transformations in the surface layer of the ground part under the influence of instantaneous grinding temperature is investigated and analyzed. This is important because the phase Feα-Feγ transformations that may occur when grinding parts lead to the appearance of so-called grinding burns, which 2-3 times reduce the reliability and durability of the part in the working mechanism. The mechanism of phase transformations, the critical temperature of these transformations and the associated processing modes that provide this temperature are determined. This allows a reasonable approach to the definition of grinding modes and, if necessary, the application of the cooling method. In addition, the problem of optimizing grinding regimes can be solved if the processing performance is taken as a target function, and grinding temperature as a limitation. With rapid surface heating of the hardened steel part by the grinding temperature above the Ac1 line, there is a reverse martensitic transformation Feα→Feγ. The martensite range during cooling Mn-Mk to a large extent covers negative temperatures. Therefore, austenite is partially fixed in the surface layer, forming a so-called quenching burn. Dependences for determining the formation temperature for steel of any chemical composition, give the possibility to maintain the value of grinding temperature below this level during grinding. The mechanism of diffusionless reverse martensitic transformation in the high-speed surface heating by cutting grains (instantaneous temperature) is considered. The heating rate and the effect of the pressure produced by the abrasive grain on the metal during the chip removal are experimentally determined. Thus, the possibility of diffusionless phase transformation is substantiated and the dependences for the calculation of austenite formation temperatures are given, which in turn provides the opportunity to calculate safe processing regimes

Superplastic diffusion bonding of metallic glasses by rapid heating

We show a superplastic diffusion bonding method to join metallic glasses (MGs) via high-speed heating at 2000 K/min taking a timescale of the order of microseconds to milliseconds at ambient pressure because the minimum viscosity of supercooled liquid drastically decreases as the heating rate increases. The results show strong metallic bonds are formed but the amorphous structure is still maintained. Finally, we establish a general equation containing the involved parameters for high-speed heating bonding. This method provides a new path to join MGs rapidly and benefits for improving the critical size of MGs.

Structure and Properties of Reinforced Ceramic Materials Produced by Directional Solidification

The paper describes advances in a promising area for the development of Samsonov’s scientific school at the Igor Sikorsky Kyiv Polytechnic Institute. The main results are provided to refine the mechanisms whereby crystals nucleate and grow from melts of eutectic alloys and acquire their microstructure and phase composition and the mechanisms whereby reinforced composite materials with isotropic and anisotropic microstructure are strengthened for extreme applications involving high-speed heating and cooling, impact interaction, cyclic loading, and corrosive environments. The mechanical properties of reinforced composite materials in a wide temperature range are presented. Areas for application of the reinforced ceramics are identified.

МАТЕМАТИЧНЕ МОДЕЛЮВАННЯ ЕЛЕКТРОМЕХАНІЧНОЇ СИСТЕМИ ПЕЧІ ШВИДКІСНОГО НАГРІВУ ПІД ЧАС ДЕМОНТАЖУ ВЕЛИКОГАБАРИТНИХ СКЛАДЕНИХ ВАЛКІВ

МАТЕМАТИЧНЕ МОДЕЛЮВАННЯ ЕЛЕКТРОМЕХАНІЧНОЇ СИСТЕМИ ПЕЧІ ШВИДКІСНОГО НАГРІВУ ПІД ЧАС ДЕМОНТАЖУ ВЕЛИКОГАБАРИТНИХ СКЛАДЕНИХ ВАЛКІВ

Investigation of the Surface Layer Structure of High-Chromium and High-Strength Steels at the Variation of the Heating Temperature

At present, hard-to-machine materials such as structural alloy steels with various chemical element additives – tungsten, chromium, etc. - are most widely used in engineering. When conventional finish methods are used for the treatment of hard-to-machine materials, the most important problems are the difficulty of obtaining work surfaces of a required quality in terms of accuracy, roughness and the physicochemical composition, and the low output. In the present paper, a finish method for metal treatment– grinding – is discussed. Zones of the formation of the surface stress state due to heating have been revealed: the zone of an insignificant increase in temperature in the contour of the contact of a grinding wheel and a work surface; the zone of the temperature intensive growth; and the zone of the temperature abrupt drop. The investigation has been conducted of the surface layer structure of high-strength and high-chromium steels during high-speed heating – grinding. The peculiarities of the change of the surface layer state of the above steels have been revealed after grinding with the use of conventional grinding wheels with a continuous cutting surface and a discontinuous cutting surface. Some recommendations are given for grinding of the high-strength 12Cr18Ni9 and high-chromium Cr12, Cr12Mo and Cr12V steels, taking into account the specific features of different technological situation characteristic of a specific grinding tool, a grinding tool grade, and conditions of grinding and cutting.

Residual Stress, Structure and Other Properties Formation by Combined Thermo-Hardening Processing of Surface Layer of Gray Cast Iron Parts

The proposed combined thermo-hardening processing of gray cast iron enables to control the surface layer structure and mechanical properties formation. The processing includes high-speed heating by low-temperature plasma source and ultrasonic surface plastic deformation. The algorithm of calculation the stress-strain state of a surface layer at combined processing of gray cast iron is developed. This algorithm is based on method of sections. The ultrasonic surface deformation contribution is determined during formation of residual stresses. It is established that the combination of the thermal and deformation effects on the material provides an additional increment of microhardness and increase of surface layer thickness. Experimental results shows that the features of structural and phase transformations in a surface layer are revealed without a surface melting by energy of low-temperature plasma. The top of a layer does not contain inclusions of graphite that testifies to change of structural transformations in conditions of combined processing.

КОНЕЧНО-ЭЛЕМЕНТНОЕ МОДЕЛИРОВАНИЕ ТЕРМОДЕФОРМАЦИОННЫХ ПРОЦЕССОВ ПРИ ИЗГОТОВЛЕНИИ ВЫСОКОПРОЧНОЙ ПРОВОЛОКИ©

The paper considers simulation of thermal strain processes while high-strength wire manufacturing. Thermal strain processing (TSP) technique was studied. Processes model consisting of wire high-speed heating up to temperatures exceeding Ас3, homogenizing soaking, workpiece straining, workpiece transfer to cooling zone under controlled and stabilized temperature providing polygonised structure formation. Simulation of thermal strain induction heating, wire drawing and reduction by running in three-roll running head was performed on the basis of conceptual functional model. Induction heating thermal field is not homogeneous within the section and depends on wire diameter, inductor transfer speed and induction heating frequency. Wire drawing shows complex state of stress, the process is axisymmetric, equivalent plastic strains are slightly different from rated strains; possible tear location on leaving the die is shown. Running equivalent plastic strains are considerably different from the rate one in terms of reduction due to tangential component. Three-roll running head application may result in higher material strengthening than it has beenpredicted during technique development on the account of pre-assigned degree of strain.

Optimization of modes of plasma treatment crane rails

Crane operation is accompanied with wear and tear of rails and crane wheels. Actual direction is the renovation and improvement of efficiency of these parts. Modern technologies of restoration of wheels and rails provide surface deposition or treatment with high-frequency currents. A promising direction is a surface treatment of highly concentrated streams of energy: with a laser beam, plasma jet. It is proposed to increase the efficiency of crane rails of surface plasma treatment. The work was carried out on the selection of treatment regimens. Simulation of the thermal impact of the plasma jet on a solid body of a complex shape was performed. Defined were multiple ranges of plasma hardening regimes that meet the requirements of production. The structural transformation of the material in the crane rails plasma treatment was investigated. It is concluded that in carbon and low alloy crane steels plasma exposure zone is characterized by a high degree of dispersion hardened structure and higher toughness as compared to the quenching with high-frequency current. Both shift (within the upper zone of plasma influence) are realized, and fluctuation (in the lower zone of the plasma effect) mechanisms of phase transformations. With high-speed plasma heating is a major transformation of granular or lamellar pearlite into austenite. The level of operational properties of hardened steel, which is achieved in this case is determined by the kinetics of the completeness and pearlite → austenite transformation. For carbon and low alloy rail steels plasma hardening of achievable properties can effectively replace the bulk hardening, hardening by high-frequency, or surface deposition. The range of conditions for plasma treatment was determined which allows to obtain a surface layer with a certain performance properties.

Methods of compacting nanostructured tungsten–cobalt alloys from Nanopowders obtained by plasma chemical synthesis

The paper summarizes the experience of using traditional and modern methods of sintering WC–Co nanopowders obtained by plasma chemical synthesis. A comparative analysis of structure formation processes occurring at sintering WC–Co nanopowders in a quasi-steady and high-speed heating is carried out. It is shown that the basic regularities of structure evolution during sintering are rather general in nature and are similar both to conventional vacuum sintering and to high-energy compaction methods. It was established that, under high-speed heating conditions, a significant contribution to the acceleration of the sintering of nanopowder materials at low temperatures is made not only by a small grain size but also the process of grainboundary diffusion. It is shown that the samples of hard alloys sintered from tungsten carbide nanopowders produced by plasma chemical synthesis have significantly higher hardness and fracture toughness than those produced using conventional synthesis techniques and compacting. Using the technology of plasma chemical synthesis and spark plasma sintering, nanostructured WC and WC–Co samples with significantly better mechanical properties (hardness, fracture toughness) than those of conventional fine materials were obtained.

Sparking plasma sintering of tungsten carbide nanopowders

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.

High-speed rotation induction heating in thermal clamping technology

The clamping technology based on high-speed induction heating of the fixing part of the system is proposed and analyzed. The continuous mathematical model of the clamping process is given by three partial differential equations (PDEs) describing the distributions of electromagnetic field, temperature field and field of thermoelastic displacements. Their coefficients containing the physical parameters of the materials are nonlinear temperature-dependent functions. The system is solved numerically in the hard-coupled formulation using a fully adaptive higher-order finite element method developed by the hp-FEM group and implemented in the application Agros2D. The methodology is illustrated with a practical example of fixing the shank of a high-revolution drilling tool in the clamping head. The results are verified by experiments.

The Mechanism of Phase Formation and Peculiarities of Mechanochemical Synthesis of Chromium Carbide

There was investigated influence of mechanical activation in centrifugal planetary mill (during 9–43 min at relation of balls mass and material B : M = 20 : 1) and subsequent high-speed heating (~ 6 °C/s) on phase formation in the system of chromium–carbon. There was elucidated that incu- bation period of carbide forming during mechanosynthesis process correlated well with thinning of interlayer of chromium in rolls like particles until length of chromium’s diffusion path into carbon. There was demonstrated that not occurred any sufficient (> 1 kJ/mol) internal energy storage in the lattice of crystalline chromium and free surface of soot. There was confirmed diffusion character of carbide forming in the system of chromium – soot as in mechanosynthesis process, both at subsequent flash heating.

Study of the Tractive Forces Applied to Galvanized Strip on a Straightening Machine in a Continuous Hot-Galvanizing Unit

Relations are presented to determine the tractive force exerted on strip by a straightening machine in a continuous hot-galvanizing unit. The working rollers of the machine have different radii. The relations take this difference into account along with the coefficient of rolling friction in the bearings of the rollers, the number of rollers in the straightening machine, the curvature of the strip, unit back tension, and the strip's mechanical properties and geometric dimensions. Results are presented from a study of how the tractive forces are affected by the cross-sectional area of the strip and the unit back tension. The results are Most of the flat-rolled products made with metallic coatings are strips and sheets with zinc and zinc-bearing coatings. In world practice, rolled strip is galvanized with the use of various types of machines and methods which differ mainly in the processes used for annealing and degreasing the metal (1-4). The accuracy of the geometry of galvanized strip is appreciably influenced by the adjustment of the straightening machine. The goal of present investigation is to examine the tractive forces applied to the strip by a straightening machine in a continuous hot-galvanizing unit (CHGU) and to develop efficient regimes for subjecting the strip to tension. The CHGU at the Mariupol Metallurgical Combine applies a wide range of coatings to strip in a broad range of widths and thicknesses. The unit controls coating thickness through the use of jets, subjects the strip to non-oxidative heat- ing, rapidly cools it in a controlled manner with a protective gas, and is equipped with an automated system that controls the overall production process (4). Among the pieces of equipment in the CHGU: uncoilers; twin shears for cropping the ends of the strip; centering rollers; welding machine; shears for trimming the sides of the strip; a horizontal storage unit that receives incoming strip; preheating furnace, high-speed heating furnace, and soaking unit; sections for rapid, slow, and final cooling of the metal; a sloping trough and a galvanizing bath; a gas cutter to control the thickness of the coating; air cooling section; a vertical unit for storing outgoing strip; temper stand; straightening machine; lubricating unit; coilers; a unit for transverse cutting of the strip; packaging machine. After the strip has been coated, it is straightened to obtain a smooth surface without shape defects. Steel strip with a thick- ness in the range 0.16-0.32 mm is straightened in straightening machines with 40-46-mm-diam. work rollers, while strip thicker than 0.32 mm is sent through straightening machines with work rollers 50-60 mm in diameter. The speed of the rollers is syn- chronized with the overall speed of the hot-galvanizing unit. Tension devices are positioned on both sides of the straightening

Electropulse consolidation of UN powder

Methods of compaction of UN powder for production of tablet fuel for next generation reactors are considered. The advantages of the method of electropulse compaction are noted. Optimal parameters of UN items production were calculated with the help of the model of the processes of high-speed heating and compaction of powder materials.

High-speed and accurate non-linear calibration of temperature sensors for transient aerodynamic heating experiments

Transient aerodynamic heating experiments with high-speed aircraft require temperature sensors that can carry out rapid and accurate electromotive force (EMF)–temperature conversions. A fast, high-precision non-linear EMF–temperature conversion method is proposed. In this method, the temperature values to be converted were pre-positioned using a non-linear mathematical model. Then, they were accurately positioned using an efficient binary search algorithm with a small scope. Thus, this method has rapid conversion speed and high calibration precision. This conversion precision is enhanced by one order of magnitude over that of the normal reference table, and the conversion time is 1% of that of the traditional piecewise linearization method. This method was employed in a transient aerodynamic heating experimental simulation system with high-speed aircraft. The experiment results show that, in the case of a high change rate of temperature and heat flux, accurate dynamic tracking can still be realized, and the experimental simulation results agree well with the pre-set environment. The developed temperature sensor calibration method is necessary for high-speed and high-precision aerodynamic heating experiments with hypersonic aircraft.