Experimental Coefficient Of Thermal Expansion Research Articles

Effect of MgO particles with in-situ graphene coating on mechanical and thermal expansion properties of aluminum matrix composites

Easy agglomeration and poor interface are bottlenecks restricting the effective transfer of internal stress in ceramic nanoparticle-reinforced metal matrix composites (MMCs). In this study, nanosized MgO particles coated by in-situ few-layered graphene (MgO@FLG) were synthesized using methane as carbon source by chemical vapor deposition (CVD) method, then incorporated with Al matrix through powder metallurgy routes. It is demonstrated that MgO@FLG particles in composites were endowed with more significant strengthening contributions in comparison with the counterparts without coating. This is critically attributed to the interlayer van der Waals of FLG promoting the particle dispersion, and the chemical interface, which involves Mg-O-C bonding and moderate Al4C3 nanorods, improving the interfacial bonding. The thermal expansion behaviors and coefficient of thermal expansion (CTE) of composites were investigated by testing thermal cycling ranging from 50 to 400 °C. The hysteresis residual strain of MgO@FLG/Al composites is less than that of MgO/Al composites, indicating a robust interface adhesion to adapt to the changing of internal stress. Furthermore, a low experimental CTE value was obtained for the MgO@FLG/Al composite, and its theoretical CTE value falls into a possible prediction region of Kerner’s model. This work provides new insights into the reinforcement modification and interface design of particle-reinforced MMCs, facing the application of structural components with the improved thermal stability and high load-bearing capacity.

Thermal expansion coefficient of nonstoichiometric gadolinium zirconate: First-principles calculations and experimental study

A high thermal expansion coefficient (TEC) is highly desirable for a thermal barrier coating material to prolong the life of the entire coating system. The TECs of Gd2-xZr2+xO7+0.5x (x = 0, ±0.125, ±0.25, ±0.375) have been studied by first-principles calculations and solid-state reactions. Due to the strong bond energy and interatomic interaction force between Zr and O, and Gd3+ having a higher thermal diffusion coefficient and lower solid solubility, the TEC of a material with higher Gd3+ content and lower Zr4+ content is improved. Calculated results show that the highest Gd3+ content (x = −0.375) increases the TEC of Gd2-xZr2+xO7+0.5x from 7.26 × 10−6/K (x = 0.375) to 8.95 × 10−6/K (1500K). The Debye temperature decreases with increasing Gd3+ content. The experimental TEC is highest (11.593 × 10−6/K) at a content of x = −0.375, far exceeding that at x = 0.375 (10.690 × 10−6/K). The experimental results agree well with the calculated results. This work lays a foundation for obtaining rare-earth zirconate materials with outstanding thermal physical properties, and it provides a novel method for their creation.

FOX-7 high-energy-density material: thermal expansion and phase transitions revisited.

Variable-temperature single-crystal diffraction experiments treated with the Gandolfi method reveal the detailed temperature evolution of the unit-cell dimensions, structural transformations and the phase co-existence of the energetic material FOX-7. Two first-order phase transitions are observed accompanied by abrupt changes in volume and unit-cell dimensions. The thermal expansion is found to be linear for all three phases, albeit highly anisotropic. Moreover, the experimental thermal expansion coefficients differ from those predicted from literature atomistic simulations.

Isotope effect on the thermal expansion coefficient of atomically thin boron nitride

Atomically thin monoisotopic hexagonal boron nitride (BN) which is electrically insulating and has a high thermal conductivity could be utilized as fillers in electronic packaging materials for thermal dissipation in integrated and miniaturized modern devices. Thermal expansion mismatch in electronic packaging could cause strain and ultimately device failure, so it is valuable to measure and understand the thermal expansion coefficient (TEC) of atomically thin isotopically pure BN. In this work, we studied the TECs of mono-, bi-, and tri-layer isotope-purified BN using Raman spectroscopy and density functional theory calculations including van der Waals dispersion forces. Monolayer (1L) 10BN had a slightly larger experimental TEC than 1L 11BN at close to room temperature: (−5.1 ± 0.8) × 10−6 K−1 and (−4.6 ± 0.8) × 10−6 K−1, respectively. The negative TECs up to 700 K were attributed to the competition between the in-plane stretching vibration modes and out-of-plane bending modes in BN; the lighter isotope leads to a larger absolute TEC due to higher amplitude of its out-of-plane bending modes. The absolute TECs of isotopic BN decreased with increased atomic thickness, which indicates strengthening of the out-of-plane bending rigidity. The deep understanding of the isotope effect on the TEC of two-dimensional (2D) materials also opens a promising pathway to minimize TEC mismatch in 2D van der Waals heterostructures.

Thermal stability and thermal expansion behavior of FeCoCrNi2Al high entropy alloy

Present work reports the thermal stability and thermal expansion behavior of dual-phase FeCoCrNi2Al HEA prepared by Mechanical Activated Synthesis and consolidated by hot pressing. The thermal stability of the phases present in FeCoCrNi2Al HEA has been extensively studied using in-situ high-temperature X-ray diffraction (HT-XRD) in conjunction with dilatometry and differential scanning calorimetry (DSC). The DSC thermogram shows a single endothermic peak at 1430 °C (1703 K) which belongs to the melting point of the alloy. HT-XRD and dilatometry experiments were carried out from room temperature to 1000 °C (1273 K). HT-XRD study has shown that the room temperature FCC + BCC (face-centred cubic + body-centred cubic) phases remains stable up to 1000 °C (1273 K). Although the amount of BCC phase has increased above 800 °C (1073 K), no additional phase formation was observed in HT-XRD. The coefficient of thermal expansion (CTE) curve shows linear increment up to 1000 °C (1273 K) with a slight change in slope beyond 800 °C (1073 K). Theoretical CTE was computed using the lattice parameter of the FCC phase, obtained from HT-XRD, as a function of temperature and compared with experimental CTE. Third-order polynomial equation was fitted to the experimental CTE data and the constants were evaluated which can be used to predict the coefficient of thermal expansion of the alloy.

Thermal expansion behavior of Al–xSi alloys fabricated using selective laser melting

Al–Si alloys are lightweight materials and show excellent mechanical and physical properties, making them appealing for automotive and aerospace industries applications. In this study, Al–(12–50 wt.%)Si alloys (nearly eutectic to hyper-eutectic compositions) were fabricated using a laser-based powder bed fusion process (LPBF) or selective laser melting technique (SLM). The microstructural evolution of the SLM Al–Si alloys as a function of increasing Si contents is investigated in detail. Refined Al and Si phases are observed and the mechanism of the refinement is discussed. In addition, the mechanical properties of the Al–Si alloy processed by casting and SLM were compared. Moreover, the influence of Si content and heating time on the coefficient of thermal expansion (CTE) of the alloys are investigated in detail, and their relationship between theoretical models and the experimental CTE values for the Al–Si alloys will be discussed and compared.

On abnormal thermal-expansion properties of more orthotropic M21E/IMA carbon-fiber-epoxy laminates

The present paper reports on an anomaly of laminates’ coefficients of thermal expansion (CTE), which has been observed for more-orthotropic laminates of a series-quality M21E/IMA prepreg-made composite frame. It was found that measured CTEs increasingly deviate from theoretical CTE values, derived from unidirectional ply data, when the degree of laminate orthotropy increases. The paper comprises experimental CTE measurements for the unidirectional M21E/IMA ply and six specific laminates of a full-scale frame. Analyses suggest that the observed discrepancy correlates with the laminates' degree of orthotropy, which is quantified by the in-plane Young's modulus ratio Ex/Ey in this paper. The observed effect is considered critical as inhomogeneous CTEs lead to process-induced distortions of curved composite structures. Thus, they play a key role when carbon-fiber-epoxy composite frames shall be made in tight dimensional tolerances. Wrong CTE calculation leads to erroneous shape predictions, inaccurate tool compensation and finally to assembly problems.

Coefficient of thermal expansion (CTE) study in metal matrix composite of CuSiC vs AlSiC

Metal matrix composites are widely used as advanced materials for thermal management applications. In view of the demands in higher temperature products application, materials with low coefficient of thermal expansion (CTE) and high thermal conductivity are required. Copper Silicon Carbide (CuSiC) is highly rated as the best materials selected for this application because it has good thermal characteristics especially in CTE, but its density is almost high for high temperature electronic device application. An aluminium silicon carbide (AlSiC) composite, on the other hand, is a new candidate for electronic device application since it has low density and good CTE characteristics. CuSiC and AlSiC composites were fabricated via powder metallurgy method through variety volume fractions such as 5%, 10%, 15% and 20%. In the present study, the comparison of CTE between CuSiC and AlSiC composites with different volume fraction of SiC particles has been carried out. The CTE of CuSiC and AlSiC composites were investigated and their responses between 25°C to 400°C were studied using horizontal dilatometer. Based on the experiment results, the density of CuSiC composites are decrease while the density of AlSiC composites is increase with increasing in SiC particles content. However, the porosity for both composites is increases with increasing in volume fraction of SiC particles. As of CTE, both composites showed decreased with increasing in SiC particles content that dispersed in their matrix. The experimental CTE values for both composites seem to be much lower than theoretical CTE value, which means that there has been excellent bonding between each particle after sintering process. The particles distribution has been observed to understand more on the aspect of SiC particles homogeneity in copper and aluminium matrix.

Temperature Sensitivity Study of Eddy Current and Digital Gauge Probes for Oxide Measurement

ABSTRACTNovel fuels are part of the nationwide effort to reduce the enrichment of Uranium for energy production. Fuel performance is determined by irradiating tfuel plates. The plate checker used in this experiment at Idaho National Lab (INL) performs nondestructive testing on fuel rod and plate geometries with two different types of sensors: eddy current and digital thickness gauges. The sensors measure oxide growth and sample thickness on research fuels, respectively. Sensor measurement accuracy is crucial because even microns of error is significant when determining the viability of an experimental fuel. One parameter known to affect the eddy current and digital gauge sensors is temperature. Since both sensor accuracies depend on the ambient temperature of the system, the plate checker has been characterized for these sensitivities. Additionally, the manufacturer of the digital gauge probes has noted a rather large coefficient of thermal expansion for their linear scale. In this work, the effect of temperature on the eddy current and digital gauge probes is evaluated, and thickness measurements are provided as empirical functions of temperature. Additionally, an experimental coefficient of thermal expansion for the probe material has been reported and compared with the manufacturer’s specifications.

Multimodal particle distribution in 3D-SiC/Al-Si-Mg interpenetrating composite fabricated by pressureless infiltration

Mechanical failure of components used in microelectronic systems is attributed to thermal stress involving temperature fluctuations, which can be eliminated by matching the coefficient of thermal expansion (CTE) of the component parts. Low CTE and high thermal conductivity (TC) 3D-SiC/Al-Si-Mg interpenetrating composites (IPCs) with monomodal or multimodal SiC distribution were fabricated by pressurelessly infiltrating Al-15Si-10Mg into high loading 3D-SiC preforms made from either a single SiC particle size or mixed SiC particles with different sizes of F220, F800 and F1000 mesh, respectively. The effect of monomodal and multimodal SiC distribution on the TC, CTE and bending strength (BS) of the IPCs were carefully studied. In general, 3D-SiC/Al-Si-Mg IPCs with optimized multimodal SiC distribution show better comprehensive properties than 3D-SiC/Al-Si-Mg IPCs with monomodal SiC distribution. The highest TC of 233.22 W/(m °C) and BS of 283 MPa as well as lower CTE of 6.32 × 10−6 °C−1 were obtained with the bimodal 3D-SiCF220/800/Al-Si-Mg IPC having a total 73% volume fraction of F220 and F800 SiC. The use of finer F1000 SiC particles in the high loading 3D-SiC preforms could lead to finer SiC particles agglomeration and not well filling in the free space left by coarse SiC network, which result in the microstructural non-uniformity, excessive Mg2Si and retained pores in the prepared IPCs causing the weakening of strength and TC of the IPCs. A significant reduction in CTE of 5.68 × 10−6 °C−1 was achieved on trimodal 3D-SiCF220/800/1000/Al-Si-Mg IPC having a total 79% SiC volume fraction. Moreover, a new model to predict the CTE of IPC based on its 3D interpenetrating network characteristics is proposed which fits well with the experimental CTE data of the IPCs.

First-principles study on the thermal expansion of Ni-X binary alloys based on the quasi-harmonic Debye model

In this study, we use the quasi-harmonic Debye model to predict the coefficient of thermal expansion of Ni- X binary alloys. The method bridges between the macroscopic elastic behavior and thermodynamic properties of materials without an expensive calculation of the volume dependence of the phonon density of states. Furthermore, the Gruneisen parameter is derived from the volume dependence of the Debye temperature, which is calculated from the first-principles elastic stiffness constants. The experimental coefficient of thermal expansion (CTE) of pure nickel is well reproduced, especially in the low temperature region. Among the few alloying elements tested, Al is predicted to slightly decrease the CTE whereas Mo and W are more effective in reducing the CTE. For the cases of Ni-X binary alloy systems, where the variation in the CTE is relatively small, the method used here appears to perform better than certain other formulations that rely entirely on the energy vs. volume relationship.

Mechanical and thermal expansion properties of SiCp/ZAlSi9Mg composites produced by centrifugal casting

Centrifugal casting was applied to produce cylindrical castings using SiCp/Al composite slurry, which contained 20% SiC particles. The castings comprised a particle free zone and a particle rich zone. The amount of SiC particles had a dramatic transformation from the particle rich zone to the particle free zone, and the maximum content of SiC particles in the particle rich zone reached up to 40 vol%. The ultimate tensile strength (UTS) of the as-cast SiCp / Al composites in the particle rich zone was 143 MPa, and the fracture was caused by the desorption of SiC particles from matrix alloy. The coefficient of thermal expansion (CTE) of the SiCp / Al composites in the range of 20 and 100 °C was determined as 16.67×10-6 s-1, and the experimental CTE was lower than the predicted data based on the Kerner’s model. The results show that the decrease in CTE in the case of the composites at high temperature stage can be attributed to the solute concentration of Si in Al and the plastic deformation of the matrix alloy in the composites with void architecture.

Thermal expansion of Carbonate-Nosean: a phase-transition kinetics model

The description of a Landau phase-transition considers group-subgroup relations with respect to the initial phase at thermodynamic equilibrium. Accordingly, the Gibbs free energy is modified in terms of an order parameter Q [1]. Data collection on a particular phase at equilibrium is challenging in case of associated kinetic effects. Thus describing a phase-transition using the Landau theory leads quite often to a marked discrepancy between the observed and calculated data close to Tc. Evaluating an accurate order parameter consequently must be a hurdle. In some cases the order parameter is proportional to the unit-cell volume of the phase. Similar effect could be seen while evaluating the lattice volume of a phase using Debye-Einstein-Anharmonicity model [2] where the internal energy of a crystalline lattice volume is considered to be sum of the Einstein harmonic, Debye quasi-harmonic and anharmonic vibrational potentials. The DEA-model gives possibility to compare the experimental thermal expansion coefficient (TEC) with that of the theoretical one. For example, in dehydrated carbonate-nosean [3] the kinetic effect close to the P23-P23 phase-transition could be seen in terms of the decrease of the TEC over several data points around 800 K (Figure). In this case, a pure Landau transition would have sharply dropped the TEC leaving no intermediate values. These deviations in the experimental data could be theoretically modeled by overlapping the TEC's of the low-temperature (TECLT) and the high-temperature (TECHT) phase using a sigmoidal term fs(T) {0 < fs(T) < 1}: TECtotal(T) = fs(T)·TEClow(T) + (1- fs(T))·TEChigh(T). The slope of this sigmoidal function corresponds to the deviation of the model used for the volume calculation close to the phase-transition and therefore carries information about the reaction kinetics. The same could be calculated for the dehydration process of the hydrated carbonate-nosean |Na8(CO3)(H2O)4|[AlSiO4]6around 400 K. Figure: Experimental temperature-dependent volume change of hydrated carbonate-nosean and respective DEA-model calculation results. The individual DEA-models as well as TEC changes including kinetic overlaps are given inserted.

Thermal expansion and mechanical properties of middle reinforcement content SiCp/Al composites fabricated by PM technology

Middle reinforcement content SiCp/Al composites (V p=30%, 35% and 40%) for precision optical systems applications were fabricated by powder metallurgy technology. The composites were free of porosity and SiC particles distributed uniformly in the composites. The mean linear coefficients of thermal expansion (20–100 °C) of SiCp/Al composites ranged from 11.6×10−6 to 13.3×10−6 K−1 and decreased with an increase in volume fraction of SiC content. The experimental coefficients of thermal expansion agreed well with predicted values based on Kerner’s model. The Brinell hardness increased from 116 to 147, and the modulus increased from 99 to 112 GPa for the corresponding composites. The tensile strengths were higher than 320 MPa, but no significant increasing trend between tensile strength and SiC content was observed.

Effect of graphene nanoplatelets on coefficient of thermal expansion of polyetherimide composite

Thermal expansion is one of the major concerns for polymer composites. In this research, graphene nanoplatelets (GNPs) were added to polyetherimide (PEId) thermoplastic polymer in order to reduce the coefficient of thermal expansion (CTE) of the injection molded composite. First, the coefficient of linear thermal expansion (LTE) was measured in three directions in the anisotropic coupon: 0°, 90° and the out of plane Z direction. It is found that the GNP particles are very effective in terms of reducing the LTE in 0° direction due to high degree of alignment. After annealing above glass transition temperature, significant increase of 0° LTE and decrease of Z° LTE were observed. The bulk CTE was calculated by adding up the LTEs in all three directions and is found to be independent of annealing. Second, several models were applied to predict both CTE and LTE. It is found that Schapery's lower limit model fits the experimental CTE very well. Chow's model was applied for LTEs in three directions. The behavior of GNP-5/PEId composites is explained by the combination of Chow's model and morphology obtained by scanning electron microscope (SEM).

Theoretical Study on the Mechanism of Anisotropic Thermal Properties ofTi2AlCandCr2AlC

Temperature dependences of thermal and elastic properties, such as the Grüneisen parameters, thermal expansion, bulk modulus, and heat capacity ofTi2AlCandCr2AlC, are studied by combining first‐principles method and lattice dynamic calculation based on the quasi‐harmonic model. Experimental thermal expansion coefficient is also measured for comparison. Thermal expansion coefficients ofTi2AlCandCr2AlCshow different trends:Ti2AlCexhibits anisotropic thermal expansion whileCr2AlCshows generally isotropic character. The mechanism is explored by investigating the isotropy or anisotropy of Grüneisen parameters (phonon anharmonicity and thermal pressure) and elastic stiffness (response to thermal pressure) ofTi2AlCandCr2AlC. In addition, the calculated bulk modulus ofCr2AlCis higher at ambient temperature but decreases faster than the value ofTi2AlCas temperature increasing.

Measurement and Evaluation of the Thermal Expansion Coefficient of Rock-Filled Concrete

Abstract Rock-filled concrete (RFC), formed by pouring self-compacting concrete (SCC) into rock blocks, is a newly developed type of mass concrete. It is important to determine its coefficient of thermal expansion (CTE) in engineering applications. In this study the CTE of RFC was determined for the first time using thermal expansion tests. RFC with three rock rates was measured at different ages. Meanwhile, the CTEs of SCC and rock blocks were experimentally tested for subsequent numerical simulation and theoretical analysis. The CTE of RFC was then evaluated numerically and theoretically based on the constituent materials. A three-dimensional finite element model was built for the numerical simulation of the thermal expansion tests of RFC. In addition, two composite models were used for the theoretical evaluation of the CTE of RFC based on the material parameters of SCC and rock blocks. The obtained numerical and theoretical CTE values agree well with the experimental CTE value. The numerical simulation and theoretical formulas can be used to estimate the CTE of RFC, thereby overcoming the high cost of complex experimental measurements.

Theoretical calculations of the thermal expansion coefficient of glass-ceramic sealing materials in solid oxide electrolysis cell

Three series of glasses, BaO–CaO–SiO2–Al2O3, SrO–SiO2–Al2O3 and SrO–CaO–SiO2–Al2O3 were prepared. The coefficients of thermal expansion (CTE) of as-cast glasses were measured using dilatometer from room temperature to their glass transition. A new method — Average Field Strength Method was developed to accurately calculate the CTEs of all glasses and compared with traditional method (Appen method). Through comparison between calculated results and experimental results, the relation between the average field strength and the average field strength coefficient was found. With the increase of average field strength, the CTE of glasses calculated by the Average Field Strength Method of glass decreases smoothly. The CTEF were very close to the experimental results. The errors between them were smaller than 3%. The error between the CTE of glasses calculated by traditional method and the experimental CTE was near 40%. The average Field Strength Method can be used to accurately calculate the CTE, and estimate the change trends of CTE.

Aging and thermal expansion behavior of Si 3N 4p/2024Al composite fabricated by pressure infiltration method

The aging and thermal expansion behaviors of Si 3N 4p/2024Al composite fabricated by pressure infiltration method were investigated. The peak-aging time and peak hardness both decrease with the increase of aging temperature for both the 2024Al alloy and Si 3N 4p/2024Al composite. The calculated activation energies of s′ (precursors of the Al 2MgCu) phase indicate that the precipitation of s′ phase in Si 3N 4p/2024Al composite occurs easily than in 2024Al alloy. The presence of Si 3N 4 particles does not alter precipitation sequence, but accelerates the process of aging precipitation in Si 3N 4p/2024Al composite. The experimental coefficient of thermal expansion (CTE) of Si 3N 4p/2024Al composite bellow 100°C is more close to the average value of the Kerner model (upper bound Schapery model) and lower bound Schapery model. Aging treated Si 3N 4p/2024Al composite presents the best dimensional stability due to low internal stress and strong pining effect on dislocations from fine dispersed precipitates (Al 2MgCu) and high density tangled dislocations. The good mechanical properties, compatible CTE with steel and high dimensional stability make Si 3N 4p/2024Al composite very competitive for application in the inertial guidance field.

A study of thermal expansion of Al–Mg alloy composites containing fly ash

The coefficient of thermal expansion (CTE) of stir cast Al–Mg alloy A535 and its composites reinforced with a mixture of 5 wt.% fly ash and 5 wt.% silicon carbide, 10 wt.% and 15 wt.% fly ash particles was investigated using thermomechanical analysis (TMA). Micromechnical models proposed by Turner, Kerner and Schapery as well as the rule of mixture (ROM) were employed to compute the CTEs of the composites within the same temperature range. Experimental results showed that the CTE of A535 decreased with the addition of fly ash and SiC particles. Subjecting the test samples to a second re-heat cycle also affected their CTE response. The CTE obtained for A535 during the first heating cycle was higher than that obtained during the re-heat cycle whereas the reverse result was obtained for the fly ash composites. Furthermore, the analytical models could not predict the experimental CTEs the composites due to complexities arising from the presence of porosities, reaction products and other defects.