Temperature Coefficient Of Linear Expansion Research Articles

Features of thermal expansion of special-purpose aluminum alloys after treatment of melt and heat treatment

A combination of corrosion resistance, low specific gravity, and high dimensional stability over a wide temperature range is necessary for alloys for special purpose. The dimensional stability is determined, first of all, by the low temperature coefficient of linear expansion (TCLE). The paper presents the results of studies on the effect of melt treatment on TCLE of aluminum alloys for special purpose on the basis of the system Al-(11÷40)%Si. It is shown that melt treatment with an aqueous solution of CuSO4 and modification of melt with a mixture of (CaCO3⋅MgCO3) leads to the decrease in TCLE for all alloys under consideration in the low-temperature test interval ttest = 50÷150 °C. Treatment of the melt by CO(NH2)2 vapours leads to the decrease of TCLE of alloys Al-40%Si in the whole temperature range from 50 to 450 °C. For high silicon alloys it is established that the decrease in TCLE occurs in the interval ttest = 350÷450°C after additional heat treatment

The aging mode for reducing the thermal expansion of the piston from alloy AK21

The effect of temperature and aging time (1÷10 h) at 100-300 °C on the microstructure and thermal expansion of the engine piston YaMZ 5363 from the hypereutectic silumin of AK21 type was studied. It is established that low-temperature aging at 100 °C for 1 hour, allows the temperature coefficient of linear expansion (TCLE) to be reduced in the operating temperature range of heavy-loaded engines (250-350 °C) by 3-6%. The increase in the aging time of pistons up to 3, 5 and 10 h does not lead to the further decrease in TCLE, as well as the increase in the aging temperature to 150, 200, 250 and 300 °C. Moreover, low-temperature aging does not lead to significant changes in the structure of the pistons of the engines in the delivery state, with the exception of coagulation of some of the volume fraction of the eutectic component of Al-Si or Al-Si-Cu.

Investigation of the thermal properties of mullite-cordierite materials

Based on the analysis of existing mullite-cordierite sitalls, the need to create high-strength materials of this type for individual and local protection against high-speed loads has been determined. They should be characterized by lower cost, due to low-temperature short-term heat treatment using domestic raw materials. An important aspect of ensuring the effective protective effect of an armor-element, in addition to its armor resistance and survivability, is the ability to withstand the effects of open flame and combustible mixtures, which is determined by the thermal properties of the sitalls. The aim of this work is to study the thermal properties, namely thermal expansion coefficient and fire resistance, high strength mullite-cordierite glass-ceramics that they are developed by us earlier. The temperature coefficient of linear expansion was determined using a quartz vertical dilatometer QVD-5A (ASTM C 372-94 (2007)), fire resistance according to GOST 33000—2014.
 According to X-ray diffraction and differential thermal analyzes, the experimental samples were divided into two groups according to the formation mechanism of structure and phase composition of glass materials during heat treatment. For each of the materials groups, the influence of the chemical and phase compositions on the thermal coefficient of linear expansion of the original mullite-cordierite glass materials and glass-ceramic materials (sitalls) thermally treated using two-stage heat treatment was determined. The study of the fire resistance of the developed glass-ceramic materials made it possible to establish that they withstand the thermal load in a certain mode for 360 minutes.
 It has been established that providing high thermal- and fire resistance (RE 360 (h)) is a determining factor in the production of hardened glass crystalline materials that are able to resist to thermal destroying at sharp temperature change.

Formation of Glaze Coatings of Clinker Bricks Based on Raw Kaolin and Aluminum-Containing Nanotechnogenic Raw Materials

The values of TCLE (temperature coefficient of linear expansion) of glaze and clinker brick on the basis of raw kaolin and aluminum-containing nanotechnological raw materials are established, and the mechanism of glaze formation during burn is established by IR spectroscopy and electron microscopy. During the glaze formation, phase separation of the glass takes place, which precedes the crystallization process. As a result of liquation, the glaze glass is divided into regions enriched in silica, zirconium, sodium, boron, and calcium. The study of heat-treated monoliths shows that the liquation structure is markedly reduced at temperatures of 700 and 950°C. The temperature interval of liquation is a function of the heat treatment conditions of the glaze. It is shown that the creek resistance of glazed clinker products is mainly due to the ratio of the mean TCLE of the mass and the glaze.

Thermoelastic Characteristics of a Composite with Anisotropic Platelike Inclusions

A mathematical model is constructed describing the thermomechanical action of the elements of a composite structure (platelike inclusion and matrix particles) and isotropic elastic medium with the required thermomechanical characteristics. The model is used at the first stage to obtain the matrix relations by the self-consistent method to find the elastic modulus of the composite. At the second stage, it is used to determine the temperature coefficient of linear expansion. Using the variation approach for the composite considered, the two-way estimates of the volumetric elasticity modulus, shearing modulus, and temperature coefficient of linear expansion are determined. The estimated dependences presented allow forecasting the thermoelastic characteristics of the composite, which is reinforced with the anisotropic platelike inclusions (including in the form of nanostructural elements).

Microcrystals of antimony compounds in lead–potassium and lead glass and their effect on glass corrosion: a study of historical glass beads using electron microscopy

Crystalline inclusions of antimony compounds in lead glass of the nineteenth century have been investigated by means of transmission electron microscopy, scanning electron microscopy, X-ray microanalysis, electron backscatter diffraction and microcathodoluminescence. Microcrystallites of orthorhombic $$\hbox {KSbOSiO}_4$$ (KSS) with the sizes ranging from about 200 nm to several micrometers have been detected in lead–potassium glass of turquoise seed beads prone to a glass disease causing the irrecoverable deterioration of beaded articles kept in museums. The KSS crystals have high number density and tend to form large colonies. Crystallites of cubic $$\hbox {Pb}_2\hbox {Fe}_{0.5}\hbox {Sb}_{1.5}\hbox {O}_{6.5}$$ have been detected in stable yellow lead glass beads. Their number density and sizes are much less than those of the KSS particles observed in turquoise glass; they do not form large clusters. We have come to conclusion that KSS precipitates are responsible for the internal strain-induced corrosion of turquoise lead–potassium glass eventually resulting in crumbling of beads to sand particles. The following scenario explains this phenomenon: $$\hbox {K}^+$$ and $$\hbox {Sb}^{5+}$$ used for glass doping form KSS crystallites during glass melting; tensile strain arising in the glass matrix during cooling because of difference in temperature coefficients of linear expansion of glass and KSS crystals gives rise to crack formation and in course of time results in glass falling apart to heterogeneous pieces. Small crystallites of $$\hbox {Pb}_2\hbox {Fe}_{0.5}\hbox {Sb}_{1.5}\hbox {O}_{6.5}$$ cannot induce a sufficient strain to break yellow lead glass, and internal cracks do not arise in this glass during its cooling. This may explain the stability of yellow lead glass.

Сhoice of materials for producing dimensionally stable load-carrying structures

The article deals with the problems of choosing materials for producing dimensionally stable load-carrying structures of space optical electronic complexes. Physical and mechanical properties of successfully applied and promising composite materials obtained by theoretical and experimental research are presented. A comparative analysis of properties of carbon-filled plastics is given according to the percentage of filler content in a composite matrix and the elastic modulus of carbon fiber. Experimental data related to the properties of carbon-filled plastics based on various fibers are presented. The dependence of the temperature coefficient of linear expansion (TCLE) of various carbon-filled plastics with unidirectional and quasi-isotropic structures is studied theoretically and experimentally. The stability of TCLE is shown to be approximately equal to110-6 ˚C-1 in the area with 50-60% volume filler content. The TCLEs and elastic moduli of carbon-filled plastics and optical glasses of telescope elements are compared. The task of developing a composite material with a TCLE value characteristic of titanium alloys is discussed. Recommendations for applying the analyzed composite materials in the development of dimensionally stable space structures are given.

Influence of Structural Components on Strength Properties of Silicate Stone Casting Materials during Controlled Crystallization

Study and description of positive effect influence of Cr2O3 catalyst in controlled crystallization technology for production of stone casting silicate materials are provided. The introduction of heat treatment method that influences the forming of the structural components of produced material. The basis of manufacturing stone casting silicate materials is controlled crystallization of silicate melt that is organized in such a way that nucleation occurs within the melt and the final product has a fine grain structure. The structural components of silicate stone casting materials and their influence on strength properties are determined. The strength of stone casting silicate materials is the reduction in the difference in the temperature coefficients of linear expansion of crystal phases and residual glass phase.

Thermophysical Properties and Temperature of the Start of Titanium Recrystallization in Different Structural States

The results of measurements of the thermal diffusivity, thermal conductivity, and heat capacity of VT1-0-grade titanium samples in as-cast, deformed submicrocrystalline, and sintered states are presented. It has been established that the decrease in the thermal conductivity and thermal diffusivity of titanium in the submicrocrystalline and sintered states is associated with the increase in the quantity of defects in the material volume, whereas the increase in the temperature of polymorphic transformation of titanium is connected with the dissolution of oxygen in its lattice. The results of investigation of the coefficient of thermal linear expansion of titanium in the macrocrystalline and submicrocrystalline states are presented. The decrease in the coefficient of thermal linear expansion of titanium of submicrocrystalline structure has been established, which may point to the decrease in its melting temperature. It is shown that annealing of samples in a submicrocrystalline state leads to the growth of the temperature coefficient of linear expansion, bringing its value closer to the temperature coefficient of linear expansion of titanium in the equilibrium state. Studies by the method of back reflection photography in a KROS chamber made it possible to estimate the temperature of the start of VT1-0-grade titanium recrystallization after intense plastic deformation by the twist extrusion method. The decrease in the temperature of the start of recrystallization for titanium in the deformed submicrocrystalline state has been established. Based on the trends revealed, optimum regimes of thermal treatment of VT1-0-grade titanium for removing internal stresses and preserving the submicrocrystalline structure have been established.

The relaxation behavior of polymer glass based on polymethylmethacrylate and its consideration in the strength calculation of aircraft glazing

The temperature–deformation–time dependences of the physical and mechanical characteristics of polymer glass based on polymethylmethacrylate necessary for the strength calculation of glazing were experimentally determined. The calculation of the residual and temperature stresses in a glazing element made of VOS-2 heat-resistant copolymer glass was performed. Ways to decrease the stresses that occur under operation by developing materials with decreased values of the elastic modulus and the temperature coefficient of linear expansion were proposed. The work was performed within complex research trend 15.4 [1] Optical Materials and Glazing Materials (“Strategic Trend of Development of Materials and Technologies for Their Processing for the Period to 2030”).

Methods of athermalization of optical systems in thermal imaging devices

Athermalization methods used in optical systems in thermal imaging devices are analyzed. Various methods of passive athermalization are considered that involve the use of structural elements with different temperature coefficients of linear expansion, as well as methods of active athermalization involving controlled axial displacement of one of the optical elements.

Precipitation Hardening of Castable Iron-Nickel Invars

Hardening of castable iron-nickel invars due to alloying with carbide-forming elements and carbon and subsequent heat treatment is investigated. It is shown that the strength of the invar alloys can be increased without raising the low values of the temperature coefficient of linear expansion.

COMPLEX MODIFICATION OF SECONDARY SILUMINS

Purpose. Development of scientific and technological bases of formation of the specified secondary hypoeutectic (АK8M3) and eutectic (АК12М2MgН) silumins' structure; and increasing their mechanical and service properties' indices in the cast state and after heat treatment up to the level of primary alloys. Methodology. Determination of the chemical composition was conducted by spectral analysis on the spark spectrometer «SPECTROLAB» (Germany). Metallographic analysis was performed on the microscopes МIМ-7 and МIМ-8, and also by the high definition metallography method using the raster electronic microscope «JSMT-300» (Japan). Heat treatment of aluminum alloys was carried out applying T1 and T5 modes according to State Standard of Ukraine 2839-94 (GOST 1583-93). Standard techniques were used during the determination of mechanical properties. The temperature coefficient of linear expansion for the piston alloy АK12М2МgH (AL25) was determined using the specimens Ø with the diameter of 3.5 mm and length of 50 mm with the use of Shevenard optical quartz dilatometer. High temperature fracture resistance was determined according to State Standard 10145-81 as the time before fracture of the specimen at specified stress of 50 MPa and temperature of 300°С. Findings. The technology of obtaining alloys from charge, which consists of 100 % scrap and production wastes has been developed and implemented into production. This technology provides obtaining of metal of the guaranteed chemical composition and high quality with the reduction of energy costs for melting. Originality. The regularities of the formation of the structural and phase state and the level of physical and mechanical properties of eutectic and secondary hypoeutectic silumins depending on the refining and modifying processes have been established. The generalization of regularities of the secondary silumins' fracture has been carried out. Quantitative characteristics of the intermetallic phases' role in the fracture mechanisms and aluminum alloys' mechanical properties level formation have been obtained. Practical value. Structure formation processes of secondary aluminium alloys depending on their production technology have been studied. Highly efficient refining and modifying complexes for treatment of secondary hypoeutectic and eutectic aluminum alloys have been developed and the optimal quantity of modifiers depending on the charge quality has been determined.

Impact of physical and mechanical properties of materials being joined on the formation of stress-strain state in the joint in diffusion welding

One of the main problems of the computer modeling of the stress-strain state (SSS) in the joint in diffusion welding (DW) is the determination and form of the given parameters of thermal and physical-mechanical properties of the materials being joined, which greatly affect the credibility of the results. This is especially true when connecting materials with structural changes in the welding temperature range. Therefore, the study of the impact of the ways of setting of the changing properties of the dissimilar materials being joined and their influence on the formation of the SSS in the joint in the thermal cycles loading is urgent. In this paper, the problem is solved in two stages. Initially, to study the impact of the ways of setting of the changing properties of the dissimilar materials being joined, the elastic problem was solved during heating and cooling in the temperature range from 700 to 1000 oC without the application of pressure and compression with it. After that, for the study of the formation of the stress-strain state at the joint with the diffusion welding thermal cycles loading, plastic solved the problem for heating and cooling with and without pressure in the same temperature range. It is shown that the difference of temperature coefficients of linear expansion of connected materials, taking into account the structural transformations in one of them, which are defined as dilatogramm, makes the most significant contribution to the formation of the stress-strain state in terms of diffusion welding. The comparison of the results of decisions of the plastic problem showed that the fundamentally received laws in solving the problem in the area of elastic deformation differs not much. It is considered that the plastic deformation in the 12H18N10T steel is practically absent during heating and cooling in the both cases of loading (the thermal loading and the purely thermal loading). In the 10864 steel the plastic deformations develop during the loading of both embodiments of junction points throughout most of the heating cycle and only in the final stage of the cooling cycle.

Thermophysical properties of ceramic materials of molds and cores for casting the heat-resistant alloy-based blades of gas-turbine engines

The thermal diffusivity, thermal conductivity, temperature coefficient of linear expansion (TCLE), and specific heat capacity of ceramic materials of shell molds and cores for casting parts of heatresistant nickel-based alloys for gas-turbine engines (GTEs) are measured in a temperature range from 20 to 1500°C by the use of methods of laser flash, relative dilatometer with a pusher, and differential scanning calorimetry (DSC). The effect of the sample thickness, various process coatings, and environment is investigated. The composition and temperature dependences of thermal diffusivity and heat expansion are considered.

Cathodes based on rare-earth metal nickelate ferrites prepared from industrial raw materials for solid oxide fuel cells

Powders of composite materials based on lanthanum nickelate-ferrite with different contents of lanthanides were synthesized using Ln-Ni-Fe-O (LnNF) mischmetal. The phase composition of the powders was determined by XRD. The crystal structure of the main phase in LnNF obtained using a mischmetal with a high lanthanum content is perovskite-like, while the structure with a high cerium content is fluorite-like. The temperature coefficients of linear expansion of the synthesized materials were determined by dilatometry. The temperature dependences of electric conductivity of the compact samples and porous electrodes from these materials were studied by the DC four-probe method. The electric conductivity of compact samples from materials prepared using the mischmetal with the perovskite-like structure of the main phase exceeds the electric conductivity of the materials based on the mischmetal with a high cerium content by approximately three orders of magnitude. The temperature dependences of polarization conductivity of electrodes in cells with the Ce0.8Sm0.2O1.9 (SDC) electrolyte at 600–900°C in air were studied by impedance spectroscopy. The LnNF electrodes with a perovskite-like crystal structure of the main phase showed high electrochemical activity.

Aluminum-Clad Invar Super Heat-Resistant Aluminium Alloy Stranded Wire Sag Calculation

Comparison with conventional ACSR aluminum clad ultra-resistant aluminum alloy invar wire with low sag, load flow characteristics, linear expansion coefficient of the wire there is migration point, the migration point temperature coefficient of linear expansion around the wire is different, therefore can not be directly calculated using the equation of state migration point directly after the aluminum clad super-resistant aluminum alloy invar wire sag. This combined with engineering examples, the wire sag derived formulas, combined with the current reality of the design units, presents a practical algorithm for reference.

Influеnce of alkaline earth metal oxides on the properties of fluor- and boron-free enamels

These days, plenty of industries widely utilize various kinds of enamelware, which must comply with State Standards, look attractive, be safe and easy-to-use. However, the production of such ware requires the enamel, containing detrimental and unhealthy impurities of fluorine as well as boron. Yet, the compounds with these elements give enamel numerous positive qualities, including fusibility, viscosity of their melt and luster of the glass coating.This article sets forth the results of analyzing the influence of alkaline earth oxides (СаО, МgO and SrO) on the fluorine- and boron-free coating enamel properties. It’s been ascertained, that the mentioned oxides have positive influence on physicochemical enamel properties (i.e. chemical resistance and the temperature coefficient of linear expansion - TCLE), as well as optical characteristics of experimental enamel coatings.The developed fluorine- and boron-free enamels can lower expenses for raw materials, preclude the lixiviation of boric oxide from enamel coatings and reduce industrial environment pollution with toxic substances (e.g. alkaline metaborates and fluorine compounds), which are emitted during the enamel melting process.The new enamels can serve as the basic materials for colored fluorine- and boron-free enamels used for coating everyday household goods.

Thermal properties and structure of cast carbon-containing invar and superinvar alloys after two-stage annealing

The effect of carbon content on thermal properties of cast superinvar alloys subjected to two-stage annealing is studied. It is shown that carbon improves the casting properties of the alloys but raises the temperature coefficient of linear expansion (CTLE). Two-stage high-temperature annealing makes it possible to remove carbon from the solid solution and to transfer it into graphite, which is accompanied by decrease in the CTLE.

Influence of ceramic properties on the stress-strain state of a plate in steady heat conduction

For ceramic cutting plates, the influence of their thermal conductivity, the elastic modulus, and the temperature coefficient of linear expansion on the stress-strain state is considered, in conditions of steady heat conduction.