Low Expansion Coefficient Research Articles

First-principles study of the third-order elastic constants and related anharmonic properties in refractory high-entropy alloys

The third-order elastic constants (TOECs) and elastic anharmonic behavior in four body-centered cubic refractory high-entropy alloys (HEAs) based on elements of the fourth, fifth, and sixth groups are investigated using density-functional simulations. We find that the values of the TOECs C111 are the largest in magnitude among the studied six independent TOECs and strongly increase with increasing average valence electron concentration (VEC). Interestingly, the TOEC C456 undergos a sign change as a function of the VEC. Using the obtained TOECs, we investigate the mode Grüneisen constants γi as well as the low temperature limit γ¯, derive the long-wavelength acoustic nonlinearity parameters β, and reveal the pressure derivatives of effective elastic constants and polycrystalline moduli as a function of the VEC. Our results show that β displays a different directional order along the pure mode [100], [110], and [111] directions for the four considered refractory HEAs. Furthermore, we show that the directional order of β is not correlated to the crystal symmetry. With the help of the obtained pressure derivatives of polycrystalline moduli, we predict the low temperature volume expansion coefficient.

The establishment of 1N·m torque standard machine at NIM

<p class="Abstract"><span lang="EN-US">1 N·m torque standard machine was established at National Institute of Metrology (NIM) in 2013. The torque standard machine adopts deadweight and moment-arm type. The static air bearing with low friction is used to support the moment-arm, the invar alloy with the low expansion coefficient as the material of the moment-arm, the specially designed weight suspension part and weight loading system may ensure the applied force by small weights accurately and reliably. The mechanical structure of the machine is introduced, the results of performance test and uncertainty assessment are described. The expanded uncertainty (<em>k </em>= 2) is smaller than </span><span lang="EN-US">5</span><span lang="EN-US"> × 10<sup>-5</sup> in the range of 100 mN·m - 1 N·m, </span><span lang="EN-US">smaller than 1</span><span lang="EN-US">× 10<sup>-</sup></span><sup><span lang="EN-US">4</span></sup><span lang="EN-US"> in the range of </span><span lang="EN-US">10</span><span lang="EN-US"> mN·m - 100 mN·m.</span></p>

The design and development of a real-time compensation controller of thermally-induced errors for CNC machine tools

Thermal deformation of the machine tool structure is one of critical factors affecting the machining accuracy level. These thermally-induced errors can account for as much as 70% of the dimensional errors on a machined work piece. Although thermally-induced errors can be reduced by applying the new materials with low-expansion coefficient to machine tools, designing the well symmetrical structure of machine tools, as well as controlling the temperature of the machining process, the costs will rise greatly. Furthermore, thermally-induced errors cannot be eliminated completely at the design stage. Hence if thermally-induced errors can be predicted, the use of indirect compensation systems will emerge as the most economical and inevitable course of action. In this paper, a real-time compensation controller of thermally-induced errors for CNC machine tools is designed and developed with the embedded technology. Test results demonstrate this compensation controller predict and compensate thermally-induced errors of CNC machine tools very well.

THE DESIGN AND DEVELOPMENT OF A REAL-TIME COMPENSATION CONTROLLER OF THERMALLY-INDUCED ERRORS FOR CNC MACHINE TOOLS

Thermal deformation of the machine tool structure is one of critical factors affecting the machining accuracy level. These thermally-induced errors can account for as much as 70% of the dimensional errors on a machined work piece. Although thermally-induced errors can be reduced by applying the new materials with low-expansion coefficient to machine tools, designing the well symmetrical structure of machine tools, as well as controlling the temperature of the machining process, the costs will rise greatly. Furthermore, thermally-induced errors cannot be eliminated completely at the design stage. Hence if thermally-induced errors can be predicted, the use of indirect compensation systems will emerge as the most economical and inevitable course of action. In this paper, a real-time compensation controller of thermally-induced errors for CNC machine tools is designed and developed with the embedded technology. Test results demonstrate this compensation controller predict and compensate thermally-induced errors of CNC machine tools very well.

Low temperature and high pressure thermoelastic and crystallographic properties of SrZrO3 perovskite in the Pbnm phase

The thermoelastic and structural properties of SrZrO3 perovskite in the Pnma (Pbnm) phase have been studied using neutron powder diffraction at 82 temperatures between 11 K and 406 K at ambient pressure, and at sixteen pressures between 0.07 and 6.7 GPa at ambient temperature. The bulk modulus, derived by fitting the equation of state to a second order Birch-Murnaghan equation-of-state, 157(5) GPa, is in excellent agreement with that deduced in a recent resonant ultrasound investigation. Experimental axial compressional moduli are in agreement with those calculated from the elastic stiffness coefficients derived by ab-initio calculation, although the experimental bulk modulus is significantly softer than that calculated. Following low temperature saturation for temperatures less than 40 K, the unit cell monotonically increases with a predicted high temperature limit in the volume expansivity of ∼2.65 × 10−5 K−1. Axial linear thermal expansion coefficients are found to be in the order αb < αc < αa for all temperatures greater than 20 K with the b axis indicating a weak, low temperature negative expansion coefficient at low temperatures. The thermoelastic properties of SrZrO3 can be approximated by a two-term Debye model for the phonon density of states with Debye temperatures of 238(4) K and 713(6) K derived in a self-consistent manner by simultaneously fitting the isochoric heat capacity and the unit cell volume. Atomic displacement parameters have been fitted to a modified Debye model in which the zero-point term is an additional refinable variable and shows the cations and anions have well separated Debye temperatures, mirroring the need for two Debye-like distributions in the vibrational density of states. The temperature dependence of the crystal structure is presented in terms of the amplitudes of the seven symmetry-adapted basis vectors of the aristotype phase that are consistent with space group Pbnm, thus permitting a direct measure of the order parameter evolution in SrZrO3. The temperature variation of the in-phase tilt, which is lost at the phase transition at 973 K, is consistent with tricritical behaviour, in agreement with published results based on high temperature crystallographic data.

An overview of the computer-integrated systems and manufacturing technologies of pistons of internal combustion engines

The technological features of manufacture of pistons of internal combustion engines (ICE) taking into account the operational characteristics that form the functional requirements of the piston material are considered. It is shown that the chill casting of pistons is recommended for alloys with a low coefficient of linear expansion, and the liquid forging of pistons is preferable to the hot forging since it allows to obtain defect-free, dense billets with the fine structure of the piston material. For the heavy-loaded diesel engine pistons, chill casting is acceptable, provided the maximum possible porosity prevention in massive parts of castings.For the simulation of the casting processes of ICE pistons, it is advisable to use the LVMFlow package since it is focused on the finite-difference computation algorithms, ensuring stable operation of the computational station at a relatively low consumption of its hardware resources, ease of interface, computation speed and low cost of the software package. For the engineering simulation of the thermal and the stress-strain state of the ICE cast pistons, the ANSYS complex that has a high interaction with existing CAD and CAE systems having full interaction with WorkbenchProducts and well-known ANSYS, as well as a large number of mathematical solvers, allowing to quickly and accurately conduct computations in the WorkbenchProducts can be recommended.

Effects of Fe&lt;sub&gt;2&lt;/sub&gt;O&lt;sub&gt;3&lt;/sub&gt; on the Properties of Iron-Red Fancy Glaze with Low Thermal Expansion (II)

In this paper, the fancy red brown glaze with suitable red spots was prepared. Effects of Fe2O3 contents on the glaze were studied. Glaze surface quality was investigated. X-ray diffraction (XRD) were analyzed the phase. The results showed that with the increase of Fe2O3 contents, the obtained sample changed from black as the base color with little red spots, to the red brown as the base color with uniform red spots, and then to the red brown as the base color with crowded red spots. It indicated that the suitable Fe2O3 content is important for good glaze surface quality with red spots. When Fe2O3 content is 10%, the iron-red fancy glaze with low expansion coefficient could be well matched with the body. It is due to the presence of petalite phase, corderite phase and a - Fe2O3 crystals.

Synthesis of cordieritic materials using raw kaolin, bauxite, serpentinite/olivinite and magnesite

In this work it was investigated whether it is attainable to create cordieritic materials for possible uses in ceramic applications using combinations of bauxite, kaolin, serpentinite/olivinite and magnesite. For this reason various mixtures of selected samples for the synthesis of ceramic materials consisting mainly of cordierite, among other phases, were used. After appropriate processing, specimens prepared from the mixtures were fired at various temperatures up to 1350°C. The ceramic materials resulted after firing, were investigated regarding their phases composition and physical properties of technological interest. On this way the creation of materials having interesting combinations of properties such as shrinkage (varied from 0.11% to 9.87%), porosity (varied from 0.6% to 38.5%), density (varied from 1.43 to 2.59g/cm3), sufficient compressive strength (range of 13.1–31.0MPa) and low coefficient of expansion (varied from 2.2 to 4.5⁎10−6/C) at high temperatures is achieved.

Phase Development During Thermal Treatment of a Fast-setting Cordierite-mullite Refractory

Cordierite based materials are widely used in high temperature applications due to their good thermo-mechanical properties and thermal shock resistance. They are generally employed in the kiln furniture (shelves, brackets, bearing plates) for firing ceramic pieces. Because of its low expansion coefficient and dielectric properties, cordierite is also used in advanced ceramics, catalyst supports automotive, industrial waste gas purification and parts subjected to sudden temperature changes. The low intrinsic strength of the cordierite may be compensated by the presence of mullite, forming a composite material of cordierite-mullite, extending its use to somewhat higher temperatures, at the expense of a slight increase in the thermal expansion coefficient. In this work a cordierite-mullite precursor was prepared from a mixture of magnesium oxide, calcined alumina, silica fume and monoaluminum phosphate solution that produces fast setting at room temperature (∼20minutes) and then, by calcination, cordierite-mullite is generated. The evolution of the mineralogical phases was studied from room temperature to 1350°C by X-ray diffraction, differential thermal analysis and thermogravimetry. A possible sequence of chemicals reactions throughout the heat treatment is also proposed. Adding refractory aggregates to this precursor leads to obtaining a fast-setting concrete, suitable for the formation of individual pieces or repair service at moderately high temperatures. A summary of its main properties is also included.

Syntheses of New Containing Ester Structure of Polyimide Materials with Low Coefficient of Thermal Linear Expansion and Low Water Absorption

Two series of new diamine monomer containing ester structure named bis(4-aminophenyl) terephthalate(BPTP) and 4-aminophenyl-4'-aminophenylbenzoate(APAB) in the main-chain were introduced in this paper. A variety of poly( ester imide) s( PEIs) was prepared using BPTP and APAB with some commercial dianhydrides. A series of poly(ester imide)s was synthesized. By the test of the thermal stability and mechanical properties,the polymers show excellent thermal stability,mechanical properties,low water absorption.Due to the introduction of the ester structure in the main chain,the polymer show a low linear coefficient of thermal expansion(CTE) and water absorption.

Effect of the Core/Shell-Structured Meta-Aramid/Epoxy Nanofiber on the Mechanical and Thermal Properties in Epoxy Adhesive Composites by Electrospinning

Aramid fibers have been widely used in fiber-reinforced composites due to their low coefficient of the thermal expansion (CTE) and high fracture toughness. However, aramid composites have poor adhesion characteristics between the fibers and the resin because the aramid fibers are chemically inert and contain insufficient functional groups. In this work, a core/shell structure of meta-aramid/epoxy nanofibers with polymer blends was prepared using electrospinning to enhance the interface adhesion of the composites. The core/shell structure of the meta-aramid/epoxy nanofibers was characterized by field emission scanning electron microscopy (FE-SEM) and transmission electron microscopy (TEM). X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared spectroscopy (FT-IR) were conducted on the nanofibers to study their chemical composition. The single-lap-joint test was performed to evaluate the adhesion strength of the metal-to-metal adhesive joint using the meta-aramid nanofiber-reinforced adhesive. An improvement in the adhesion strength of the reinforced epoxy adhesive used to generate meta-aramid/epoxy nanofibers was achieved through in-situ nanointerface core/shell structure formation by electrospinning.

Effect of nano/micro-mixed ceramic fillers on the dielectric and thermal properties of epoxy polymer composites

Nano/micro ceramic-filled epoxy composite materials have been processed with various percentage additions of SiO2, Al2O3 ceramic fillers as reinforcements selected from the nano and micro origin sources. Different types of filler combinations, viz. only nano, only micro, nano/micro, and micro/micro particles, were designed to investigate their influence on the thermal expansion, thermal conductivity, and dielectric properties of epoxy polymers. Thermal expansion studies were conducted using thermomechanical analysis that revealed a two-step expansion pattern consecutively before and after vitreous transition temperatures. The presence of micro fillers have shown vitreous transition temperature in the range 70–80°C compared with that of nano structured composites in which the same was observed as ~90°C. Similarly, the bulk thermal conductivity is found to increase with increasing percentage of micron-size Al2O3. It was established that the addition of micro fillers lead to epoxy composite materials that exhibited lower thermal expansion and higher thermal conductivity compared with nano fillers. Moreover, nano fillers have a significantly decisive role in having low bulk dielectric permittivity. In this study, epoxy composites with a thermal expansion coefficient of 2.5 × 10−5/K, thermal conductivity of 1.18 W/m · K and dielectric permittivity in the range 4–5 at 1 kHz have been obtained. The study confirms that although the micro fillers seem to exhibit good thermal conductivity and low expansion coefficient, the nano-size ceramic fillers are candidate as cofillers for low dielectric permittivity. However, a suitable proportion of nano/micro-mixed fillers is necessary for achieving epoxy composites with promising thermal conductivity, controlled coefficient of thermal expansion and dielectric permittivity. Copyright © 2013 John Wiley & Sons, Ltd.

Heat-Resistant Wrought Weldable Alloy for GTE Components with Low Linear Thermal Expansion Coefficient

Features of the effect of alloying elements on linear thermal expansion coefficient of wrought heat-resistant alloys based on the Ni–Fe system are studied. Short-term and long-term strength at 600°C is simulated and parameters are used successfully as equivalent alloy chemical composition, calculated by a system of unpolarized ionic radii equations. A new deformable weldable alloy based on Ni–Fe–Co is developed with working temperature up to 650°C, with $ \upsigma_u^{20 } $ = 1400 MPa, $ \upsigma_u^{600 } $ = 1200 MPa, and $ \upsigma_{100}^{600 } $ = 950 MPa, with low linear thermal expansion coefficient (α = 11.8 · 10–6 K–1 in the temperature range 20–600°C). The alloy is structurally stable, efficient in forming and welding, and with respect to set of properties it is better than standard alloys of similar designation. New alloy structure, phase composition, and properties are described.

Experimental Study of Temperature Effect on Oil Relative Permeability in Porous Media

In the modeling of thermal recovery processes of heavy oil, it is important to know the oil primary relative permeability in the reservoir; moreover we have to be aware of effects of the temperature on oil relative permeability as well. In this study, a sand pack of quartz (SiO2) has been used to simulate and make a porous medium. Quartz is naturally water wet. During experiments there was no change in the pore volume of the media at different temperatures because of the low expansion coefficient of quartz. The fluid used in experiments is engine oil 50. Glass pipes with length of 91cm and diameter of 2.6cm have been used in the experiments. At first, columns have been filled with sand, which sand grains had different diameters, then carbon dioxide was injected to the columns to deplete the air in the pores , then the porous media have been saturated with water to calculate the porosity using the scale model. In addition according to Darcys law in steady state, the absolute permeability was calculated. In the next step, oil was injected to columns until the water saturation reached connate water saturation and finally, water injection was begun to get residual oil saturation (Sor). Experiments results showed that increase of temperature increases the oil relative permeability, note that wetability was constant. Increasing the temperature decreases the oil viscosity then this reduction causes the fluid to move easier and its velocity increases as well.

THE DESIGN OF 1 N•M TORQUE STANDARD MACHINE AT NIM

A 1 N•m torque standard machine has been designed and developed at National Institute of Metrology (NIM) since 2011. The torque standard machine adopts the moment arm-deadweight type, the air bearing with low friction is adopted to support the moment-arm at the fulcrum, the invar with the low expansion coefficient is used as the material of the moment-arm, the weight suspension part and weight loading system are specially designed to ensure the applied force by small weights accurately and reliably. This paper introduces the mechanical structures of the machine, the electrical control system is described. 1 N•m torque standard machine is capable of realizing the torque from 1 mN•m to 1 N•m both in clockwise and anti-clockwise directions.

Investigation on high temperature fracture properties of amorphous silicon dioxide by large-scale atomistic simulations

Amorphous silicon dioxide exhibits low temperature expansion coefficient and stability of dielectric properties over a wide range of frequencies and temperatures, and plays an important role in integrated circuits and microelectronics. Downscaling of dimensions in there devices means great challenges for thin film reliability and physical characterization. Mechanical failure caused by stresses in thermal conditions is the major reliability issues for electronic devices. As the experiments have limitations in micro/nano-scale characterization of fracture properties at high temperatures, atomistic simulation is a proper way to investigate this particular mechanism. In this paper, the structural and fracture properties of amorphous silicon dioxide (a-SiO2) were studied at temperatures up to 1,500 K. The simulation results consist with the experiments on pair distribution function, structure factor, angular distributions and temperature-dependent Young’s moduli. The calculated Young’s modulus is close to the simulation and experimental results of 72.5–78.9 GPa for SiO2, and begin to drop after 900 K With temperature increasing.

Analytical model of transient temperature and thermal stress in continuous wave double-end-pumped laser rod: Thermal stress minimization study

A time-dependent analytical thermal model of the temperature and the corresponding induced thermal stresses in continuous wave double-end-pumped laser rod are derived from the first principle using the integral transform method. The aim of the paper is to study the effect of increasing the pumping powers while the laser crystals are still in the safe zone (i.e. far away from failure stress) and to suitably choose a crystal that achieves this task. The result of this work is compared with a well-verified finite element solution and a good agreement has been found. Some conclusions are obtained: Tm:YAP crystal, which has high thermal conductivity, low expansion coefficient, low absorption coefficient, low thermal factor and low product of γE/(1− υ), is the best choice to reduce induced stress although it is responded and brought to thermal equilibrium faster than the other types of crystal usually used in the end-pumped solid-state laser.

Effect of Different Nucleating Agents on the Microstructure and Properties of LMAS Glass-Ceramics

Li2O-MgO-Al2O3-SiO2(LMAS) system glass-ceramics had been prepared by sintering method. The effect of different nucleating agents on the phase composition, microstructure and properties of LMAS system glass-ceramics were investigated by DTA, XRD and SEM. The results indicate that the introduction of nucleating agents could contribute to decreasing the crystallization temperature of the glass-ceramics, the effect of the nucleating agent TiO2 is most obvious, and the crystallization temperature is the lowest(798.9°C). Main crystal phase of the glass-ceramics without the nucleating agents is β-quartz solid solution, while main crystal phase of the glass-ceramics with different nucleating agents changes into β-spodumene solid solution. The glass-ceramics with composite nucleating agents (TiO2+ZrO2+P2O5) are the lowest coefficient of thermal expansion (0.86×10-6/°C)and the highest flexural strength (95MPa). Composite nucleating agents have the best effect of crystallization, and contribute to the formation of a large number of short columnar crystals, which is the main reason for obtaining glass-ceramics with low expansion coefficient and high flexural strength.

Overaged metallography of alloy 909, a low coefficient of expansion superalloy

The microstructure of alloy 909, a low coefficient of thermal expansion Fe-Co-Ni superalloy was examined in the solution treated and over aged condition, following a previous communication by the authors on the solution treated and commercially aged alloys. In the commercially aged alloy, only the Laves and the γ‚ phases were observed. With some indication, however, of alignment of the γ‚ phase along crystallograpic directions in the austenitic matrix. This alignment of the γ‚ phase has been previously reported as a precursor to the growth of the ϵ phase from the γ‚ phase. Analysis by TEM showed that the platelet phase was hexagonal (NiFeCo)2(TiNb) with some variations in the stoichiometry about 2:1 ratio. Tensile and hardness testing indicated that the presence of the platelet shaped ϵ phase in the solution treated and overaged condition was not as effective in the strengthening of the alloys as the spherical γ‚ in the commercially aged and solution treated condition. In addition to the presence of ϵ phase, blocky A2B Laves phase was abundant, which prevents excessive grain growth up to ∼1040°C

Influence of mechanochemical activation on the sintering of cordierite ceramics in the presence of Bi 2O 3 as a functional additive

Due to its outstanding electrical characteristics, such as the low temperature expansion coefficient, low dielectric constant and good mechanical properties, cordierite, 2MgO⋅2Al 2O 3⋅ 5SiO 2, is a very attractive high-temperature ceramic material. In order to accelerate the process of sintering, 2.50 mass% Bi 2O 3 has been added to the starting mixtures. Liquid phase sintering caused by the presence of bismuth-oxide lowers the temperature of cordierite formation. The mechanical activation of the starting mixtures (0–56 min in vibro-mill) additionally lowers sintering temperatures. The sintering process was performed at 1200, 1300, 1350 and 1400 °C, for 2 h. The particle size analysis (PSA) was employed in order to determine the changes in the particle size of the mechanically treated powders. The phase composition of the starting powders and sintered materials was analyzed by the X-ray diffraction method. Furthermore, scanning electron microscopy (SEM) was used in the analysis of the powder morphology.