Thermal expansion

About: Thermal expansion is a research topic. Over the lifetime, 21040 publications have been published within this topic receiving 349407 citations. The topic is also known as: heat expansion.

Effect of the Grain Boundary Thermal Expansion Coefficient on the Fracture Toughness in Silicon Nitride

Abstract: The effect of thermal expansion mismatch stress between silicon nitride and different grain boundary phases on the fracture toughness of silicon nitride was investigated. Different sintering aids in the Y-Mg-Si-Al-O-N system produced silicon nitride specimens with very similar microstructures but different grain boundary phase compositions and different values of fracture toughness. The fracture toughness of the silicon nitride increased as the thermal expansion coefficient of the grain boundary phase increased. The presence of tensile residual stress at the grain boundary caused by thermal expansion mismatch between the silicon nitride and the grain boundary phase enhanced crack deflection and grain bridging.

Polymorphism of Ti 3 SiC 2 ceramic: First-principles investigations

Abstract: The Nanolaminate Ti3SiC2 ceramic exhibited unique mechanical properties, such as high modulus, low anisotropic hardness to modulus ratio and microscale ductility etc. The planar close-packed Si atoms were expected to play a dominant role in deducing these properties. By performing first-principles total energy calculations, we demonstrated that a reversible polymorphic phase transition occurred when shear strain energy was large enough to close an energy barrier. The phase transition path was described as the Si atoms sliding between 2b and 2d Wyckoff positions on the (11(2) over bar 0) plane. The electronic band structure, lattice dynamics, and structure stability were discussed for the two polymorphs, respectively. We demonstrated that the alpha-Ti3SiC2 was more stable than beta-Ti3SiC2 by comparing the ground-state total energy and ab initio Gibbs free energy. Raman and infrared active phonon modes were illustrated for feasibly identifying the two phases in experimental spectra. The results were used to assign peaks in the experimental Raman spectrum with distinct vibrational modes, and to clarify the origin of the uncertain peak. The calculated heat capacity and volume thermal expansion coefficient agreed with experimental values well. The elastic mechanical parameters of the polymorphs were presented and compared with respect to various strain modes. Based on electronic band structure discussions, we clarified the mechanism of anisotropic hardness of Ti3SiC2, which attributed to different covalent bonding strengths involved in kink migration.

Thermal expansion and crystal structure of FeSi between 4 and 1173 K determined by time-of-flight neutron powder diffraction

Abstract: The thermal expansion and crystal structure of FeSi has been determined by neutron powder diffraction between 4 and 1173 K. No evidence was seen of any structural or magnetic transitions at low temperatures. The average volumetric thermal expansion coefficient above room temperature was found to be 4.85(5) × 10−5 K−1. The cell volume was fitted over the complete temperature range using Gruneisen approximations to the zero pressure equation of state, with the internal energy calculated via a Debye model; a Gruneisen second-order approximation gave the following parameters: θD=445(11) K, V0=89.596(8) A3, K0′=4.4(4) and γ′=2.33(3), where θD is the Debye temperature, V0 is V at T=0 K, K0′ is the first derivative with respect to pressure of the incompressibility and γ′ is a Gruneisen parameter. The thermodynamic Gruneisen parameter, γth, has been calculated from experimental data in the range 4–400 K. The crystal structure was found to be almost invariant with temperature. The thermal vibrations of the Fe atoms are almost isotropic at all temperatures; those of the Si atoms become more anisotropic as the temperature increases.