Assuming that heat is transported by lattice vibrations (phonons) in silicate glasses, their thermal conductivity is correlated with the product of sound velocity, volumetric heat capacity, and phonon mean free path (MFP). The sound velocity and heat capacity have been studied extensively, but the origin of the composition-induced variation in the MFP remains unclear. The present study investigated MFP in M_2/nO–SiO₂ (Mⁿ⁺: Li⁺, Na⁺, Ca²⁺, Sr²⁺, or Pb²⁺) glasses with a variation of M_2/nO content. The MFP of the silica glass decreased with the addition of M_2/nO. The effect of the type of metallic cation on the MFP was minimal for the selected alkali and alkaline-earth silicate glasses. By contrast, the MFP of lead silicate glasses was higher than those of alkali or alkaline-earth silicate glasses when the metallic cation contents were comparable. Previous studies have demonstrated that alkali and alkaline-earth cations act as nonframework species that break the silicate network structure, whereas lead cations have inconclusive structural roles. Our data indicate that lead cations partly act as framework cations and that phonons tend to be scattered near nonframework cations in silicate glasses. Thus, the phonon MFP is a useful parameter for determining the structural role of metallic cations in silicate glass via phonon propagation.

The effect of dislocation density on the σ phase precipitation behavior in KA-SUS304J1HTB was investigated. The specimen was pre-strained by room-temperature uniaxial tensile test and subjected to ageing at 700°C. The number density and area fraction of the σ phase after ageing increased with the amount of pre-strain. On the other hand, the pre-strain had no significant effect on the average σ phase diameter. Electron backscatter diffraction (EBSD) analysis revealed that the geometrically necessary dislocation (GND) density was increased with the amount of pre-strain. Moreover, the GND density of the pre-strained specimens showed little change after the ageing. The EBSD analysis also revealed that the GND density was significantly higher around the grain boundaries compared to the grain interior. Using the GND density around the grain boundaries in the pre-strained specimens, the change in the number density of the σ phase during ageing was calculated based on the classical nucleation theory. The calculated number density of the σ phase showed good agreement with the experimental results. This result implies that the effect of the pre-strain on the number density of the σ phase after ageing can be explained by the change in GND density around the grain boundaries.

The effect of χ phase precipitated at the grain boundary of matrix on the high temperature mechanical properties of ferritic Fe–Cr–Ni–Al–Mo alloys containing nano-sized B2-type NiAl precipitates was investigated. It was found that the grain boundary of Fe–22Cr–6Ni–6Al–3Mo alloy was covered with the χ phase approximately 95% by a heat treatment at 800°C for 50 h. However, the average particle diameter of the NiAl precipitates increases to approximately 300 nm during this heat treatment. We found that the NiAl precipitates can be refined to approximately 27 nm by additional heat treatment above the dissolution temperature of the NiAl precipitates followed by air cooling. The alloy with nano-sized NiAl precipitates and the χ phase exhibits a yield stress of 235 MPa at 700°C. The suppression of intergranular fracture by grain boundary strengthening caused by the χ phase and precipitation strengthening due to the nano-sized NiAl precipitates are responsible for the high strength of the alloy at high temperatures.

To elucidate the mechanisms of deformation and a state of plastic stability at the front of Lüders bands during a tensile test, metastable austenitic transformation-induced plasticity (TRIP) steels with different dislocation densities and ferritic steels were characterized via macroscopic-DIC-based stress–strain investigations and scanning electron microscopy (SEM). A direct correlation between stress–strain curves and measured strain distributions in the tensile specimen indicated that the Lüders front represents a transition region from a state of plastic instability to one of stability, whereby a general rule relating the Lüders strain (Δε_L*) and increments in the true stress in the Lüders band (Δσ_L*) to a lower yield stress (σ_y0*) can be described as σ_y0*=Δσ_L*Δε_L* irrespective of the amount of deformation-induced martensite in the band or crystal structure of the steel. The inclination angle of the Lüders front with respect to the tensile direction changed from 55° to 90° with a reduction in the measured strain ratio (−ε_yy/ε_xx) in the Lüders band, and the change agreed with the tendency calculated by the plasticity model assuming the pure shear deformation under the minimum shear strain criterion. SEM observations of the sheet surface and the front cross-section in the TRIP steel revealed the formation of multiple inclined ~20 μm-wide shear deformation zones that accompanied a reduction in thickness. All the observed geometrical characteristics of the Lüders front are qualitatively explained by minimizing the misalignment from the fixed tensile axis caused by shear mode deformation.