The changes in the states of carbon (C) together with hardness and tensile properties of low C steel (0.045C-0.34Mn in mass％) quenched from 710℃ and aged at 50℃ were investigated as a function of aging time using TEM and atom probe tomography. Vickers hardness commences to increase at about 1.1 × 10⁴ s, exhibits significant increase at 5.8 × 10⁴ s (16 h) and keeps peak hardness till 8.6 × 10⁵ s (10 d) followed by decrease after further aging time. In the beginning of peak aging, C clusters form having irregular shape close to a sphere with the diameter of about 10 nm. The number of C atoms is about 700 atoms, and the C content is in the range of 1 - 2 at％ at 1.0 × 10⁵ s (28 h), where enrichment of elements except for C is not observed. Meanwhile in the end of peak aging, the precipitates with the plate shape (about 1 nm in width and 12 nm in length) having the C content of more than 10 at％ are distributed with the {100} habit plane. The transition from C clusters to fine carbides was confirmed. Lower yield strength (LYS) is the lowest for the specimen with solute C, and significantly increases for the specimen with C clusters and fine carbides in this order. LYS is inferred to be determined by the cutting mechanism for C cluster specimen and presumably Orowan mechanism for fine carbide specimen. The work hardening for solute C specimen and C cluster specimen is high, while carbide specimen shows less work hardening. C cluster is postulated to be decomposed into solute C by being sheared by dislocations, causing work hardening and relatively good uniform elongation. Post uniform elongation (l-El) was the lowest for C cluster specimen followed by fine carbide specimen with the same strength level. This is because dynamic strain aging caused by solute C promotes the strain localization leading to the deterioration in l-El.

To investigate the effect of the surface texture of steel on the crystal orientation relation between Fe and Zn, we deposited Zn at 1500 A・m⁻² and 1.48 × 10⁴ C・m⁻² onto both Al-killed and IF steel sheets in an agitated sulfate solution at 313 K. Chemically polishing the steel simplifies the deposition of Zn epitaxially because of the decreased strain in the steel surface. For Zn deposited on Al-killed steel, the Burgers' orientation relation of {110}Fe//{0001}Zn was completed after the chemical polishing of the steel. In this case, because the orientation of {111}Fe increased and Zn was deposited according to the orientation relation of {110}Fe//{0001}Zn, the orientation of {0001}Zn decreased. In contrast, for Zn deposited on IF steel, the preferred relation was {111}Fe//{0001}Zn. The crystal-grain size of IF steel is larger than that of Al-killed steel, which makes the epitaxial growth of Zn easier on IF steel than on Al-killed steel. The orientation of {111}Fe was more prominent in IF steel than in Al-killed steel. Because the proportion of {0001}Zn increases under conditions where the epitaxial growth of Zn occurs easily and the orientation {111}Fe was more prominent in IF steel, this appears to be the cause of the relation of {111}Fe//{0001}Zn. The orientation relation between the deposited Zn and steel changes based on the strain, crystal orientation, and grain size of the steel. Therefore, the crystal orientation of the deposited Zn changes as well.

A diffusion-barrier coating layer (DBC) was formed on a Ni-22Cr-19Fe-9Mo alloy by Al-pack cementation at 1000℃ followed by heat treatment at 1100℃．The thermal cyclic oxidation behavior of the DBC system was then investigated. The thermal cycle oxidation tests were conducted at 1100℃ in air for 45 min, each followed by 15 min at room temperature. Electron probe micro-analysis (EPMA) was performed to determine the microstructure and concentration profile of each element between the substrate and the coating layer.

The DBC system showed good thermal cycle oxidation property. The layer structure between the substrate and the coating layer after thermal oxidation cycling is discussed with respect to the composition paths plotted in the Ni–Cr–Fe and Ni–Cr–Al phase diagrams. The coating layer structure after 100 cycles of 45 min at 1100℃ consisted of the γ- and α-phases of the Ni–Cr–Fe system and the β-phase of the Ni–Cr–Al system. The coating layer structure after 400 cycles of 45 min at 1100℃ consisted of the γ-phase of the Ni–Cr–Fe system and the β-phase of the Ni–Cr–Al system. In contrast, the coating layer structure after 900 cycles of 45 min at 1100℃ consisted of the γ-phase of the Ni–Cr–Fe system.

A thermodynamic assessment of the Al-Cu-Mg ternary system was attempted using the first-principles calculation and CALPHAD approach. For Laves phase to which polymorphic structures are known, the Gibbs free energies of formation were evaluated by applying the cluster expansion and cluster variation method to each structure of C14, C15 and C36. Furthermore, concerning the free energies of formation of Al₂Mg and Cu₂Mg as the end-members of these structures, entropy of the lattice vibration was considered. This procedure results in more accurate evaluation of the free energy of formation for the Laves phase. As for the ε (Al₃₀Mg₂₃) phase and CuMg₂ phase that the thermodynamic properties were not well clarified, formation energies were also evaluated. Thermodynamic analysis was accomplished by an introduction of the result based on these first-principles approach as well as some experimental data in the framework of the CALPHAD method. According to the calculated result, it is suggested that the structural transformation in the Laves phase occurs in the Cu rich side than the previously reported composition region. Solidification process of a commercial Al alloy was discussed using the Scheil-Gulliver simulation.

Microstructural alterations such as white band (WB) including low angle band (LAB) and high angle band (HAB) following the formation of dark etching area (DEA) in bearing steels below the contact surface due to high stress rolling contact fatigue (RCF) were investigated. Although there have been many studies on the characteristics of WB, its formation mechanism has not been sufficiently clarified yet. In this paper, we analyzed the orientation of crystal constituting WB and investigated the relationship between WB and the direction of shear stress generated by rolling contact. The morphology of WB as a function of depth from surface was observed by light optical microscope, and the crystal orientation was analyzed by scanning electron microscope–electron backscattering diffraction. It was found that LAB and HAB formed at the depth where the principal shear stress and the orthogonal shear stress become maximum, respectively. Crystal orientation analysis of LAB and HAB revealed that crystal rotates under the principal shear stress at the specific depth, resulting in the formation of unique texture such as {111}<211> and {122}<411>, respectively. Thus, WBs were proved to be some kind of shear band. WB formation behavior of specimens with the different amount of initial retained austenite (γ_R) was compared in order to clarify sub-surface initiated spalling life improvement mechanism by γ_R. However, the WB formation behavior showed no difference irrespective of the amount of initial γ_R. This suggests that the WB formation is not directly related to sub-surface initiated spalling life.