Variation Of Thermal Expansion Coefficient Research Articles

The effect of thermomechanical treatment on the electrodeposited Invar alloy for FMM

Fine metal masks (FMMs), which are applied to manufacture next-generation organic light-emitting diode (OLED) displays with ultra-high definition (UHD) or higher, must have thicknesses of <10 μm to eliminate shadow zones. To manufacture FMMs with a thickness of 10 μm or less, a bottom-up electroplating process must be applied. The minimum coefficient of thermal expansion (CTE) of the as-deposited electroplated Invar alloy is 4 ppm; subsequent thermal treatment can lead to a CTE of zero. However, sample conditions such as surface wrinkles and edge curls may appear during this thermal treatment process. The effect of varying treatment parameters, including pressure and temperature, on the shape of the electrodeposited Invar alloy is investigated in this study by performing a thermomechanical treatment that can regulate the ultrathin FMM shape. Depending on the Ni composition, the electrodeposited Invar alloy may exist as a singular α-BCC phase or a mixed γ-FCC phase during electrodeposition. During thermomechanical treatment, a phase transformation occurs from the electrodeposited α-BCC phase to the γ”-FCC phase, and wrinkles occur owing to uneven volume change. Additionally, curls are formed owing to CTE variations according to the ratio of phases from the electrodeposition surface to the final surface varies during the plating process. Based on these results, process conditions that facilitate shape control of ultra-thin electroplated FeNi alloys were proposed.

First principles investigation of thermodynamic property of diamond under high pressure and high temperature

The present study utilizes the density functional theory to obtain the diamonds’ thermodynamic properties up to 2000 K and 100 GPa under the quasi-harmonic approximation. The results reveal that the variation of thermal expansion coefficient and heat capacity with temperature can be categorized into three distinct temperature regions within the range of 10–2000 K. These regions are accurately described by the Debye model, a combination of Debye and Einstein models, and the Einstein model, respectively. Additionally, high pressures raise the upper temperature limit applicable to the Einstein model. And the study successfully explained the variation of Grüneisen coefficient under high-temperature and high-pressure conditions using the proposed model. In the temperature range where both Einstein and Debye models yield accurate results, the influence of pressure enhances the contribution of the Debye model to the thermal expansion coefficient and heat capacity of diamond, resulting in a higher peak in the Grüneisen coefficient.

Doping induced phase transition, elastic, electronic, vibrational and thermal properties of LiBeA1-x Sb x (A= P and As)

ABSTRACT Phase transition, elastic, electronic, vibrational and thermal properties of (A = P and As) are investigated via performing ab-initio calculations combined with the virtual crystal approximation (VCA) and the quasi-harmonic Debye model. Our total energy results show that and undergo a phase transition from the (P4/nmm) phase to the polar LiGaGe (P) one beyond antimony concentration of x = 0.21 and 0.36, respectively. The calculated elastic constants show that the studied alloys are mechanically stable and they also exhibit abrupt discontinuities at the transition concentrations. From Poisson's ratio and the B/G ratio, both alloys are brittle. Our results indicate that the studied alloys are semiconductors and the gap value decreases as Sb concentration increases. The calculated phonon dispersion curves for different antimony concentrations have positive frequencies. The phonon frequencies at the zone centre for the Raman-active and infrared-active modes are predicted for the and the LiGaGe structures for different antimony concentrations. The value of the polarisation is almost constant for different values of concentration. The variations of thermal expansion coefficient (α), bulk modulus (B), Debye temperature (), heat capacities at constant volume (C) and the parameter (γ) as a function of pressure and temperature were all obtained and analysed in detail.

Processing and evaluation of nano SiC reinforced aluminium composite synthesized through ultrasonically assisted stir casting process

Aluminium composites were synthesized through an ultrasonically assisted stir casting method by reinforcing 0.5 wt%SiC, 1.0 wt%SiC, 1.5 wt%SiC and 2.0 wt%SiC nanoparticles. Ultrasonication was carried out to the composite melt to refine the grain size and to achieve uniform nano-SiC dispersion in the aluminium matrix. Scanning electron microscopy (SEM) reveals the uniform dispersion of nano-SiC particles in the 0.5 wt%, 1.0 wt% and 1.5 wt% SiC reinforced compose. However, the X-Ray Diffraction (XRD) peaks confirm the Al2Cu intermetallic phases in the Al- 2.0 wt% SiC composite. The mechanical properties of the synthesized composites were significantly enhanced with the incorporation of SiC reinforcements and the maximum hardness and ultimate tensile strength (U.T.S) of 163 BHN and 431 MPa was attained for 1.5 wt% SiC reinforced composite. Nevertheless, the generated brittle agglomeration at 2.0 wt% SiC reinforcements decreases the mechanical properties of the composite due to the variation of thermal expansion coefficients between the matrix and the agglomerations. The yield strength of the fabricated Al– SiC composites was analyzed through different strengthening mechanisms. Results concluded that the yield strength contribution due to thermal mismatch is more influenced followed by the Orowan strengthening and grain refinement strengthening mechanism. In addition to this, the contribution of the strengthening mechanisms was found to be increased with the addition of SiC nanoparticles. Fractography investigation for the fractured tensile specimens reveals the ductile fracture for unreinforced aluminium and brittle fracture for the SiC-reinforced composites due to the presence of cleavage texture of the fractured surfaces of Al–SiC nanocomposites.

Investigating the Underlying Effect of Thermal Modification on Shrinkage Behavior of Bamboo Culm by Experimental and Numerical Methods.

This study probes into the root cause of split in thermally modified bamboo culm by investigating the underlying effect of thermal contraction with respect to its orthotropic nature by experimental and numerical methods while concurrently monitoring the chemical variation of its structure by Fourier transformed infrared spectroscopy (FTIR). In first part of this study, a non-linear increase in dimensional and weight changes of small clear bamboo specimens were observed with increasing temperature. The dimensional changes in the radial and tangential directions significantly exceeded that in the longitudinal direction. From FTIR results, shrinkage effect between 150 °C to 200 °C was associated with weight loss engendered by reduction in weakly bound water and increase in desorption of water content while alteration of its mechanical properties was attributed to changes in cellulose, hemicellulose, and lignin. From results of finite element method (FEM), the graded variation in thermal expansion coefficient, which showed the formation of a narrowed region of strain concentration corresponding to longitudinal crack propagation, was associated with the inducement of internal forces, namely tensile and compressive forces, at specific regions along the culm length. The results of this study can be useful to achieve optimized durability in modified bamboo for construction.

Contributions of mechanical bonding and chemical bonding to high-temperature hermeticity of glass-to-metal compression seals

The present work compares the contributions of mechanical bonding and chemical bonding to high-temperature hermeticity of glass-to-metal (GTM) compression seals and explores their temperature-dependent failure behaviors. The GTM compression seals were fabricated using pre-oxidized AISI 304 and borosilicate glass with different thermal expansion coefficients (TECs). The variation of TEC was investigated by changing the alkali oxides contents. The chemical bonding strength between the glass and the pre-oxidized AISI 304 was evaluated using shear strength test and fracture surface analysis. And the mechanical compressive stress was analyzed by fiber Bragg grating technology at elevated temperature. In addition, the seal hermeticity with varying temperature under high pressure helium was also recorded. The results show that the hermeticity failure temperature increases as compressive stress attenuation reduces. But the contribution of increasing chemical bonding strength to high-temperature hermeticity is covered up by that of compressive stress decay. This demonstrates that mechanical bonding has a stronger influence on high-temperature hermeticity of the seals than chemical bonding. The findings of this work will guide the development and optimization of GTM compression seals towards further improvement of the high-temperature tolerance.

Effects of Concrete Age on Coefficient of Thermal Expansion of Paving Mixes and Its Significance in Unbonded Overlay Design

Abstract With the advancement in rigid pavement design and advent of AASHTOWare Pavement Mechanistic-Empirical (ME) Design (American Association of State Highway and Transportation Officials, Washington, DC) as the latest design tool, increasing emphasis is being laid on the coefficient of thermal expansion (CTE) of concrete. The CTE affects the performance of rigid pavements in a significant manner, with a higher CTE corresponding to greater curling and resulting in greater pavement distresses. Prior research has conflicting views regarding CTE variation with age, and there has been very little to no research on the effects of CTE on the performance of unbonded concrete overlays (UBCOs). This study is performed to investigate the variation of CTE with concrete age through laboratory testing and further quantify the effects of CTE variation on UBCO design. To facilitate, four concrete paving mixes with different types of coarse aggregates and different mix properties from different districts of New Mexico were collected. The cast specimens from each of the mixes were tested for CTE as per the AASHTO T-336, Coefficient of Thermal Expansion of Hydraulic Cement Concrete, protocol, at the ages of 7, 14, 28, 60, 90, 120, and 180 days, respectively. The test results were analyzed, and it was observed that there is an increase in CTE over the range of 3.49 % to 9.77 %, between 28 days and 180 days. Further analysis was conducted with simulations in Pavement ME Design Version 2.3® that indicated a significantly deteriorated performance of the UBCO with increased CTE. The impact on transverse cracking and joint faulting is the most significant, with up to 13.3 % increase in cracking and up to 19.7 % increase in faulting distress. An unbonded overlay designed with 28 days CTE value may not perform for the design life because of the increase in CTE with age progression.

Variation of thermal expansion coefficient of freestanding multilayer pristine graphene with temperature and number of layers

The in-plane coefficient of thermal expansion (CTE) of freestanding multilayer pristine graphene was directly measured by the thermal bulge method using a white light interferometric microscope. Graphene ribbons with 3, 5, and 10 layers were prepared by exfoliation of high-quality graphite flakes and then transferred over 60–120 μm wide trenches in a Si substrate. A novel transfer procedure was developed to achieve the freestanding configuration. All the measured CTE values were negative in the temperature range of 25–150 °C, and their absolute values decreased with increasing temperature and number of layers. The CTE of monolayer graphene can be approximated to about −7 × 10−6/°C. It was speculated that a structure with more than 12 layers was graphite rather than graphene.

The thermal effect on dynamic characteristics of composite material pipe conveying fluid

Based on thermoelasticity, the composite material pipe is studied in this paper with the variation of thermal expansion coefficient and temperature. Considering the thermal effect, a model called elastic Bernoulli-Euler beams is developed to analysis the buckling and vibration. The partial differential equations are established by using Hamiltonian principle. The static post-buckling problem is studied by eigenvalue method after Galerkin method. By harmonic balance method, the approximate solution of strong nonlinear vibration is obtained. The effect of thermal effect on vibration is also focused. The simulation shows that the thermal effects make conveyor pipes more vulnerable to instability, and has obvious influence on the dynamic characteristics. The research content is more practical than the dynamic analysis of the conveyor pipe without considering the temperature effect.

Tunable coefficient of thermal expansion of Cu-B/diamond composites prepared by gas pressure infiltration

Cu-B matrix composites reinforced with diamond particles (Cu-B/diamond) were prepared by gas pressure infiltration (GPI). The effect of boron addition in the range of 0–1.0 wt% on the thermal expansion behavior of the Cu-B/diamond composites was evaluated. The coefficient of thermal expansion (CTE) of the Cu-B/diamond composites initially decreases and then increases with increasing boron content. The minimum CTE value of 4.88 × 10−6/K is obtained at 0.5 wt% B addition, which satisfies the requirement of CTE of semiconductors (range of 4–8 × 10−6/K) for electronic packaging applications. The variation of CTE of the Cu-B/diamond composites is attributed to the formation of interfacial carbides and their morphological evolution. The interface structure evolves from discrete triangular carbides into continuous carbide layer with increasing boron content. The increase in the quantity of discrete carbides enhances the interface, but the formation of continuous carbides impairs the interfacial bonding of the Cu-B/diamond composites. The results suggest that alloying B to Cu matrix is an effective route to tune the coefficient of thermal expansion of Cu/diamond composites.

A new test setup for measuring early age coefficient of thermal expansion of concrete

Coefficient of thermal expansion (CTE) of concrete changes at early ages mainly due to microstructural modifications that occur during cement hydration. This paper proposes an innovative way to assess the CTE of concrete since very early ages, with the original inclusion of an internal heating/cooling system, that allows to speed up the thermal balance cycles, and increase the number of CTE measurements during the early ages. The method comprises a specimen of 154 mm diameter and 300 mm height, submitted to successive heating and cooling steps with thermal variations of 5 °C, right after casting. A spiral heating/cooling tube, embedded in concrete, is used to circulate the controlled temperature water bath inside the specimen. This paper demonstrates the feasibility of the strategy for accelerating thermal equilibrium of the specimen, both experimentally and through numerical simulation. The short duration of the thermal cycle in this proposal strongly increases the ability of the method in capturing the early kinetics of CTE evolution, allowing to measure the CTE as soon as 4.1 h after mixing. With durations of each full temperature cycle of 1.5 h, it was possible to obtain as many as 12 CTE measurements within the first 24 h of testing, which is an important improvement in regard to similarly sized specimens in the literature. Furthermore, when the information obtained from the proposed test method is combined with the continuous feed about E-modulus of concrete that can be obtained through application of the EMM-ARM technique, very definite conclusions can be attained about the expectable stress levels that can be attained in concrete elements at early ages, due to the early variation of CTE. Three concrete mixtures are used to verify applicability of the proposed method for measuring early age CTE of concrete. The calculated values for these concrete mixtures are in agreement with the data found in the literature.

Effect of temperature on vibrations and buckling behavior of carbon nanotube-based mass sensors using a new temperature-dependent structural model

In last decade, structural mechanics (SM) approach has been one of the most known and effective tools for the determination of the mechanical properties of carbon nanotubes (CNTs) such as elastic modulus, shear modulus, natural frequency, and critical axial buckling strain. Considering increasing applications of CNTs as resonators at low and high temperatures, a new temperature-dependent structural mechanics model is presented here. The proposed model can be utilized to predict the effect of temperature on the mechanical response of CNTs as functional resonators. Mechanical and geometrical properties of equivalent beam element are correlated to the CNT's coefficient of thermal expansion (CTE). Owing to elaborate series of finite element simulations, the frequency shift of a CNTs-based mass sensor with different attached mass and aspect ratio in temperature range of 0–1600 K is calculated. Afterwards, the critical buckling temperature of CNTs-based mass sensor due to increasing the axial force by changing ambient temperature is obtained. Results show that decreasing the first natural frequency is clearly appeared by attaching a mass more than about 1 zg on the CNTs structure. In other words, CNTs can be used to detect particles with mass above 1 zg. Moreover, it is shown that the variation of CTE versus temperature is a critical parameter that influences the vibration and buckling behavior of CNTs-based mass sensors. Increasing temperature leads to decreasing natural frequency due to rising axial forces along the CNTs axis. As a result, the natural frequency approaches to zero when the temperature rises up to the critical buckling temperature. In addition, increase in temperature over the critical buckling temperature changes the mode shape of CNT vibration to the next mode shape.

High-temperature mechanical properties and thermal cycling stability of Al-50Si alloy for electronic packaging

With the rapid development of electronics industry, there is an increasing demand for high performance electronic packaging materials. Furthermore, the high-temperature performance and thermal cycling stability are required owing to the harsher service environment. In this work, Al-50Si alloy was prepared via rapid solidification/powder metallurgy technique, and the tensile properties at elevated temperature and the thermo-physical properties after thermal cycling were investigated. The results show that the tensile strength decreases gradually with the increase in the environmental temperature. Whereas, pullout of the Si particle is seldom observed in the specimens at elevated temperatures owing to the strong interfacial bonding. With the progress of thermal cycling, the coefficient of thermal expansion (CTE) is stable, but the plastic strain increases rapidly at the initial stage. However, the thermal conductivity decreases significantly with the increase in the temperature or the number of thermal cycles. This phenomenon is mainly ascribed to the CTE mismatch between the Al matrix and Si phase. The variation of CTE and thermal conductivity is discussed in terms of thermally induced stress.

Research on the thermal expansion of AgGa1−xInxSe2 single crystals

Thermal expansion coefficients of AgGa1−xInxSe2 (x = 0.2, 0.3, 0.4) single crystals have been measured in the range from 323K to 823K. The values of αa are positive and increase with temperature whereas the values of αc are negative and their absolute magnitudes increase with the increasing temperature for different x. With the increase of x, thermal expansion coefficients αa and αc both decrease numerically. The mean linear thermal expansion coefficient αL and the anisotropy of thermal expansion αη have been calculated, and they are also decreasing numerically with the increasing x. The slope of the straight line αhkl versus cos2ϕ decreases as x increases at 473K and 773K, respectively. According to the variation of thermal expansion coefficients, the relationship between the thermal expansion coefficient, bond length, and melting point of AgGa1−xInxSe2 satisfies the equation αL=0.021Tm−B(d−d0)3. In addition, the mechanism of thermal expansion variation has been discussed in terms of crystal structure, bond lengths, and thermal vibration of bonds in AgGa1−xInxSe2 single crystals.

Dilatometry Analysis of Dissolution of Cr-Rich Carbides in Martensitic Stainless Steels

The dissolution of Cr-rich carbides formed in the martensitic constituent of a 13 pct Cr stainless steel was studied by dilatometry and correlative electron channeling contrast examinations. The dissolution of carbides subsequent to the martensite reversion to austenite was associated with a net volume expansion which in turn increased the dilatometry-based apparent coefficient of thermal expansion (CTEa) during continuous heating. The effects of carbides fraction and size on the CTEa variations during carbides dissolution are discussed.

Influence of Small Weight Percentages of Bi and Systematic Coefficient of Thermal Expansion Variations on Sn Whiskering

In Part A of this paper, we have investigated how small, controlled amounts of Bi influence Sn whiskering. Three custom Sn–Bi sputter targets of 0.5%, 1.0%, and 2.0% Bi (by weight) were used to generate $\sim 2000$ A Sn films on Si substrates. The samples were incubated at room temperature (RT) followed by thermal cycling ( $- 40 ) to accelerate whisker growth. The control group was not thermal cycled. Whisker densities dramatically dropped to zero as the concentration of Bi increased to 2.0% for the RT specimens (100-day incubation). However, subsequent thermal cycling turned ON whisker growth ( $\sim 25$ 000 whiskers/cm $^{\mathrm {\mathbf {2}}}$ ) in all the three Bi% cases. Thus, Bi additions suppress whiskering during RT incubation, but the same films readily grow whiskers during thermal cycling. In Part B, a systematic range of coefficient of thermal expansion (CTE) variations between the substrate and Sn (pure, i.e., no Bi or Pb) were investigated to determine the effect on whisker growth. CTEs close in value to Sn ( $0 ) were Al, Ag, and brass; intermediate in value to Sn ( $25 ) were Zn, Ni, and Ta; and far in value to Sn ( $75 ) were semiconductors Si, GaAs, and InP. A thickness of 0.5 $\mu \text{m}$ of sputtered Sn was deposited on each coupon. The thermal cycling range was −40 °C to 125 °C, with 2-h ramps and 4-h dwells, for a total of 12 h per cycle. A second, comparative set of specimens underwent isothermal annealing at 100 °C. All the samples were incubated for 37 days (74 cycles) before observation. The results show that samples with a % $\Delta \text {CTE} >75$ % had drastically higher whisker densities (when cycled) compared to those with % $\Delta \text {CTE} %. There appears to be a critical activation (or nucleation) threshold CTE mismatch that “turns ON” whisker growth when using semiconductors as substrates.

Investigation of Thermal Expansion and Physical Properties of Carbon Nanotube Reinforced Nanocrystalline Aluminum Nanocomposite

Abstract Carbon nanotube (CNT) reinforced nanocrystalline aluminum matrix composites are fabricated by a simple and effective physical mixing method with sonication. In this study, the microstructural characterisations and property evaluations of the nanocomposites were performed. The structural characterisations revealed that CNTs were dispersed, embedded, and anchored within the metal matrix. A strong interfacial adhesion appeared between CNTs and nanocrystalline aluminum as a result of the fabrication process. Raman and Fourier transform infrared spectroscopic studies also confirmed the surface adherence of CNTs with nanocrystalline aluminum matrix during the fabrication process. Thermal expansion behaviour of CNT-reinforced aluminum matrix composites was investigated up to 240°C using a dilatometer. The coefficient of thermal expansion of the nanocomposites decreased continuously with the increasing content of CNTs. The maximum reduction of 82% was found for 4 wt% CNTs in the nanocomposite. The coefficient of thermal expansion variation with CNTs was also compared with the predictions from the thermoelastic models. The expansion behaviour of the nanocomposites was correlated to the microstructure, internal stresses, and phase segregations. The electrical and thermal conductivity was also studied and was observed to decrease for all reinforced CNT weight fractions.

Effect of specimen size and grain orientation on the mechanical and physical properties of NBG-18 nuclear graphite

We present here a comparison of the measured baseline mechanical and physical properties of with grain (WG) and against grain (AG) non-ASTM size NBG-18 graphite. The objectives of the experiments were twofold: (1) assess the variation in properties with grain orientation; (2) establish a correlation between specimen tensile strength and size. The tensile strength of the smallest sized (4mm diameter) specimens were about 5% higher than the standard specimens (12mm diameter) but still within one standard deviation of the ASTM specimen size indicating no significant dependence of strength on specimen size. The thermal expansion coefficient and elastic constants did not show significant dependence on specimen size. Experimental data indicated that the variation of thermal expansion coefficient and elastic constants were still within 5% between the different grain orientations, confirming the isotropic nature of NBG-18 graphite in physical properties.

Correlation of Ionic Conductivity of Lithium Borosilicotitanate Glasses with Structure

Lithium ion conducting glasses containing TiO2 have been prepared by the conventional melt quenching technique. Electrical conductivity σdc, activation energy Ea, density ρ, molar volume Vm, coefficient of thermal expansion (CTE) and glass transition temperature Tg for all the glass samples were measured. The variation of electrical conductivity with addition of TiO2 in lithium borosilicate system has been studied. The FTIR spectroscopy has been used for structural studies of these glasses. The decrease in conductivity with the addition of TiO2 at the cost of modifier Li2O is explained on the basis of changes in glass structure revealed by the IR spectrum which is also supported by the Tg, density and CTE variation. The electrical modulus spectra of the glasses have been studied to understand the conduction mechanism.

Effect of Nano Grain Growth on Coefficient of Thermal Expansion in Electroplated Fe-Ni Invar Alloy

The aim of this paper is to consider the effect of annealing on the coefficient of thermal expansion (CTE) of electroplated Invar Fe-Ni alloy. The CTE of the as-electroplated alloy is lower than those of alloys annealed at <TEX>$400^{\circ}C$</TEX> and <TEX>$800^{\circ}C$</TEX>. XRD peaks become sharper as the as-electroplated alloy is annealed, which means the grain growth. The average grain sizes of as-electroplated and as-annealed alloys at <TEX>$400^{\circ}C$</TEX> and <TEX>$800^{\circ}C$</TEX> are 10 nm, 70 nm, and <TEX>$2{\mu}m$</TEX>, respectively, as determined by TEM and EBSD analyses. The CTE variation for the various grain sizes after annealing may come from the magnetostriction effect, which generates strain due to changes in the magnetization state of the alloys. The thermal expansion coefficient is considered to be affected by nano grain size in electroplated Fe-Ni Invar alloys. As grain size decreases, ferromagnetic forces might change to paramagnetic forces. The effect of lattice vibration damping of nano grain boundaries could lead to the decrease of CTE.