Thermal and Mechanical Properties of Refractory High‐Entropy Alloy Composites with TiC in Nonequal Molar CrMoNbTaTiZr at Elevated Temperatures

Thermal properties of graphene/metal composites with aligned graphene

Thermal expansion properties of the polycaprolactam nanocomposites reinforced with single-walled carbon nanotubes

Polymer Matrix Composite Thermal Materials

Elaborately designed polymer dielectric films with low coefficient of thermal expansion demonstrating high and stable electrostatic energy density over a wide temperature range

Thermal expansion studies of Li2TiO3 by dilatometry and in-situ high-temperature X-ray diffraction

Mitigating thermally induced stress in epoxy polymers is significantly challenging. An effective strategy of preparing a dual-functional epoxy vitrimer with a low coefficient of thermal expansion (CTE) and rapid stress relaxation was developed to mitigate stress. The epoxy vitrimer was synthesized using AFG90, a dicarboxylic acid, and a dibenzocyclooctadiene (DBCOD)-based motif (DBCOD-NH2). The samples exhibited low or even negative thermal expansion below their Tg, owing to the conformational transition of the DBCOD unit, and rapid stress relaxation above the Tg, owing to the carboxylate transesterification of the dynamic ester bonds. The two functions operated independently over different temperature ranges. One of the typical samples exhibited a CTE of -21.8 ppm/K (40-70 °C) and a stress relaxation time of 268 s (240 °C). Structure-property correlation revealed that increasing the DBCOD-NH2/dicarboxylic acid ratio or decreasing the dicarboxylic acid chain length could decrease the thermal expansion and slow the stress relaxation owing to the variation in the content of DBCOD or dynamic bonds and the increased chain rigidity and cross-link density. Stress relaxation could be further enhanced using the synergistic effect of dual dynamic bonds while maintaining the low thermal expansion. This strategy is promising for mitigating thermally induced stress in epoxy matrices.

AlSi7Mg/SiC/70p (AlSiC) is used for heat sinks because of its good thermal conductivity combined with a low coefficient of thermal expansion (CTE). These properties are important for power electronic devices where heat sinks have to provide efficient heat transfer to a cooling device. A low CTE is essential for a good surface bonding of the heat sink material to the insulating ceramics. Otherwise mismatch in thermal expansion would lead to damage of the bonding degrading the thermal contact within the electronic package. Therefore AlSiC replaces increasingly copper heat sinks. The CTE mismatch between insulation and a conventional metallic heat sink is transferred into the MMC heat sink. The stability of the interface bonding within a MMC is critical for its thermal properties. In situ thermal cycling measurements of an AlSi7Mg/SiC/70p MMC are reported yielding the void volume fraction and internal stresses between the matrix and the reinforcements in function of temperature. The changes in void volume fractions are determined simultaneously by synchrotron tomography and residual stresses by synchrotron diffraction at ESRF-ID-15. The measurements show a relationship between thermal expansion, residual stresses and void formation in the MMC. The results obtained from the in situ measurements reveal a thermoelastic range up to 200 °C followed by plastic matrix deformation reducing the volume of voids during heating. A reverse process takes place during cooling. Thus the CTE becomes smaller than according to thermoelastic calculations. Damage could be observed after multiple heating cycles, which increase the volume fraction and the size of the voids. The consequence is local debonding of the matrix from the reinforcement particles, which leads to an irreversible reduction of the thermal conductivity after multiple heating cycles.

Synthesis and thermal behavior of Cu/Y2W3O12 composite

Tunable thermal properties in yttrium silicates switched by anharmonicity of low-frequency phonons

Three dimensional AlN skeleton-reinforced highly oriented graphite flake composites with excellent mechanical and thermophysical properties

Metal matrix nanocomposites (MMNCs) with high specific strength have been of interest for numerous researchers. In the current study, Mg matrix nanocomposites reinforced with AlN nanoparticles were produced using the mechanical stirring-assisted casting method. Microstructure, hardness, physical, thermal and electrical properties of the produced composites were characterized in this work. According to the microstructural evaluations, the ceramic nanoparticles were uniformly dispersed within the matrix by applying a mechanical stirring. At higher AlN contents, however, some agglomerates were observed as a consequence of a particle-pushing mechanism during the solidification. Microhardness results showed a slight improvement in the mechanical strength of the nanocomposites following the addition of AlN nanoparticles. Interestingly, nanocomposite samples were featured with higher electrical and thermal conductivities, which can be attributed to the structural effect of nanoparticles within the matrix. Moreover, thermal expansion analysis of the nanocomposites indicated that the presence of nanoparticles lowered the Coefficient of Thermal Expansion (CTE) in the case of nanocomposites. All in all, this combination of properties, including high mechanical strength, thermal and electrical conductivity, together with low CTE, make these new nanocomposites very promising materials for electro packaging applications.

This study presents colorless polyimides (PIs) suitable for use as plastic substrates in flexible displays, designed to be compatible with controlled soft adhesion and easy delamination (temporary adhesion) processes. For this purpose, we focused on a PI system derived from norbornane-2-spiro-α-cyclopentanone-α′-spiro-2″-norbornane-5,5″,6,6″-tetracarboxylic dianhydride (CpODA) and 2,2′-bis(trifluoromethyl)benzidine (TFMB). This system was selected with the aim of exhibiting excellent optical transparency and low linear coefficient of thermal expansion (CTE) properties. However, fabricating this PI film via the conventional two-step process was challenging because of crack formation. In contrast, modified one-pot polymerization at 200 °C using a combined catalyst resulted in a homogeneous solution of PI with an exceptionally high molecular weight, yielding a flexible cast film. The solubility of PI plays a crucial role in its success. This study delves into the mechanism behind the significant catalytic effect on enhancing molecular weight. The CpODA/TFMB PI cast film simultaneously achieved very high optical transparency, an extremely high glass transition temperature (Tg = 411 °C), a significantly low linear coefficient of thermal expansion (CTE = 16.7 ppm/K), and sufficient film toughness, despite the trade-off between low CTE and high film toughness. The CpODA/TFMB system was modified by copolymerization with minor contents of another cycloaliphatic tetracarboxylic dianhydride, 5,5′-(1,4-phenylene)-exo-bis(hexahydro-4,7-methanoisobenzofuran-cis-exo-1,3-dione) (BzDAxx). This approach was effective in improving the film toughness without sacrificing the low CTE and other target properties. The peel strengths (σpeel) of laminates comprising surface-modified glass substrates and various colorless PI films were measured to evaluate the compatibility with the temporary adhesion process. Most colorless PI films studied were found to be incompatible. Additionally, no correlation between σpeel and PI structure was observed, making it challenging to identify the structural factors influencing σpeel control. Surprisingly, a strong correlation was observed between σpeel and CTE of the PI films, suggesting that the observed solid–solid lamination is closely linked to the unexpectedly high surface mobility of the PI films. The laminate using CpODA(90);BzDAxx(10)/TFMB copolymer exhibited suitable adhesion strength for the temporary adhesion process, while meeting other target properties. The modified one-pot polymerization method significantly contributed to the development of colorless PIs suitable for plastic substrates.

The paper focuses on thermal and electrical properties of copper–graphite composites. Copper–graphite composites in the range of 0–50 vol% of graphite were prepared from the mixture of copper and graphite powder by the powder metallurgy method. Such composites combine high thermal and electrical conductivities provided by copper matrix and low thermal expansion coefficient and lubricating properties due to the graphite phase. We model thermal and electrical conductivities and thermal expansion coefficient using methods of micromechanics in connection with the material microstructure and measure these quantities experimentally to compare with the results of modeling. Cross-property connections between thermal and electrical properties of the composites are established and experimentally verified.

Carbon foams (CFms) exhibit excellent physical properties, including good thermal con-ductivity, low density, high porosity and specific surface area, good vibration damping and shock absorption properties, and low thermal expansion coefficients. These properties are attractive in various applications such as thermal and electrical transfer devices, electro-chemical supercapacitors, catalyst supports, gas adsorbents, filtration systems, and electro-magnetic shielding. However, compared to metals and polymers, CFms do not exhibit good mechanical or thermal properties because of their porous structure; these shortcomings have limited the application of CFms in various fields [1-4].Researchers have sought to improve the mechanical and thermal properties of CFms through the addition of carbon nanofibers, carbon nanotubes, graphite and metal plating [5,6]. CFms/copper composites were recently studied by Johnson et al. [7], who examined the thermal conductivity of wood-derived graphite and copper-graphite composites pro-duced via electrodeposition. The thermal conductivity of the biomorphic graphite/copper composite was 10 times greater than that of biomorphic graphite, with the graphite/copper composites exhibiting a thermal conductivity ranging from 20 to 21 W/mK [7]. Zhai et al. [8] studied the effects of vacuum and ultrasonic co-assisted electroless copper plating on CFms and noted increased conductivity ranging from 700 to 1885.8 S/cm, and increased compres-sive strength ranging from 0.70 to 1.66 MPa with increasing copper content. Cu exhibits high thermal and electrical conductivities, in the range of 350-400 W/mK and 59.17-59.59 × 10

Abstract