Microstructure and phase equilibria and stability of Ti and Al co-added MoSiBTiC alloys were investigated for Mo-xTi-5Si-3Al-10C-10B (in mol％) alloys (xTi-3Al alloys) and Mo-xTi-5Si-5Al-10C-10B (in mol％) alloys (xTi-5Al alloys) (x = 15-30). In the as-cast state after arc-melting, lower-Ti-content alloys had the constituent phases of Mo_ss, Mo₅SiB₂ (T₂), TiC and Mo₃(Al,Si). After primary TiC crystallization, Mo_ss+TiC, Mo_ss+T₂+TiC and Mo₃(Al,Si)+TiC eutectic phases were crystallized out in stages during solidification. At and above the Ti concentration of 20 mol％, Mo_ss+Ti₅Si₃ eutectic was also observed to form in finally solidified regions. On the other hand, no Mo₃(Al,Si) was crystallized in the 25Ti and 30Ti-3Al alloys, and the 30Ti-5Al alloy. After heat treatment at 1600℃ for 24 h, the Mo_ss+Ti₅Si₃ eutectic phase observed in finally-solidified regions disappeared. The volume fraction of Mo₃(Al,Si) decreased with increasing Ti content, and in the 25Ti and 30Ti-3Al alloys and the 30Ti-5Al alloy, no Mo₃(Al,Si) appeared. As a result, the constituent phases were Mo_ss, T₂, and TiC in the 25Ti and 30Ti-3Al alloys and the 30Ti-5Al alloy as same as those of the first generation MoSiBTiC alloy. For all the alloys, the partitioning ratio of Ti for Mo_ss/Mo₃(Al,Si) was over 1, meaning Ti stabilizes Mo_ss against Mo₃(Al,Si). Accordingly, it is concluded that Ti expands the solubility limit of Al in Mo_ss and suppresses Mo₃(Al,Si) formation in the MoSiBTiC system.

The effects of thickness (t), grain size (d), ratio t/d, and tensile direction on tensile properties were carefully examined using ASTM grade 1 pure titanium having strong B texture with controlled thickness (0.2-0.4 mm), grain size (20-175 mm), and t/d (2.3-19.4). 0.2％-proof stress followed a Hall-Petch relationship in each tensile direction regardless of thickness, and this indicates that 0.2％-proof stress does not depend on t/d. On the other hand, tensile strength and uniform elongation were confirmed to depend on t/d and significantly decreased in some thin sheets, in comparison with thick sheets with the same grain size, except for the case tested in the transverse direction. Namely, both tensile strength and uniform elongation exhibited a drastic decrease when t/d becomes smaller than the critical values. The critical value of t/d depended on tensile direction and decreased with an increasing tensile angle in the rolling direction. Local elongation increased with decreasing grain size except for the case tested in the transverse direction. In addition, local elongation was not related to t/d. Tensile properties that depend on t/d are inferred to be affected by work-hardening behavior, enhanced by twinning deformation in hcp titanium. However, the formation of deformation twinning in the surface regions was found to be suppressed, presumably due to the relaxed, constrained conditions. Consequently, the work-hardening rate decreased with decreasing t/d because of the attribution from the surface region where twinning deformation is retarded.

The importance of controlling grain boundary (GB) segregation is increasing with the strengthening of steel. In this study, a theoretical prediction method for the amount of GB segregation for a solute element in polycrystals, is established. In this prediction method, a nano-polycrystalline GB model for simulating GBs in polycrystals is developed, and the segregation energy of a solute element is calculated comprehensively for all atomic sites constituting the GB model by using an interatomic potential. From the obtained segregation energies, the segregation amount of the solute element at each atomic site is determined. Subsequently, each atomic site is classified for based on its distance from the GB center, and averaged to calculate the segregation profile of the solute element for that distance from the GB center. By applying this method to the GB segregation of P in bcc-Fe and comparing its results with experimental findings, it is determined that this prediction method can attain a good prediction accuracy.

The surface morphological change of electro-deposited Pt–75 at％ Cu (Pt–75Cu) nanoparticles under potential cycling were investigated by identical-location scanning electron microscopy. Electro-deposited nanoparticles consisted of numerous nuclei (～3 nm in diameter) that agglomerated to form larger secondary particles (30-50 nm). In the initial immersion in the sulfuric acid, Pt-shell formed on the surface due to the selective dissolution of Cu from Pt-75Cu. Although around 40％ of Cu dissolved, noticeable surface morphological change does not appear. Then Pt-75Cu was subjected to potential cycling between 0.05-1.0 V, surface smoothing of the nanoparticles slightly progressed due to surface diffusion of Pt. On the other hand, when Pt-75Cu was potential-cycled between 0.05-1.4 V, a particle diameter of the nanoparticles drastically decreased, and the nucleus on the surface completely disappeared owing to Pt dissolution and re-deposition. The heat-treated nanoparticles formed numerous pores on the surface during the immersion and the initial stage of the potential cycle. However, the final morphology was similar to the non-heated one. The formation of pores can be explained by the coarsening of nuclei by heat treatment.