Sukeharu Nomoto

Experimental Study on Phase Diagram in the Vicinity of X or W Phase in the Mg-Zn-Y Ternary System

To elucidate the phase equilibria in the vicinity of the X or W phase in the Mg-Zn-Y ternary system, five Mg-Zn-Y ternary alloys containing the X or W phase were prepared and isothermally heat-treated to reach thermodynamic equilibrium. The microstructure and chemical compositions of the equilibrium phases of the alloys were analyzed. Furthermore, the crystal structure of the W phase was investigated, and the liquidus temperatures of the alloys were examined using differential thermal analysis. The results showed that the X phase can be crystallized not by a eutectic reaction, as reported previously, but by a peritectic reaction. They also showed that the W phase has the Heusler-type crystal structure with a stoichiometric composition of Mg1Zn2Y1, and that Mg and Zn in the W phase can be substituted for each other. The Mg-Zn-Y ternary phase diagram was calculated using an assessed CALPHAD thermodynamic database based on the experimental results of the present study, and compared with a recently reported phase diagram.

Progress in R&D for YBCO Coated Conductors by TFA-MOD Processing

Recent progress in the research and development of the TFA-MOD processing for the coated conductors is reviewed. For the higher Ic performance, process conditions such as heating rate and water vapor inlet temperature in the calcination step and heating rate and water vapor pressure in the crystallization step have been optimized to obtain YBCO films with good crystallinity. Consequently, a high Ic value of 431A/cm-w was achieved by the combination of the above optimized conditions with the use of highly textured CeO2 cap layered substrates. Forwards the effort for long tape fabrication with high production rate, the multi-turn system for coating and calcination step was developed. Additionally, the reel-to-reel system for the crystallization step was developed for the longer tape, and a 25m long YBCO tape with a reasonable end-to-end Ic value of 100A, which corresponds to 2500Am as a product of IcxL, was obtained by the above continuous system. For the higher production rate in the crystallization step, it was confirmed that optimization of the processing parameters such as high water partial pressure, high diffusion constants due to low total pressure, and a high gas flow rate affects the YBCO growth rate.

Solidification Simulation of Fe–Cr–Ni–Mo–C Duplex Stainless Steel Using CALPHAD-Coupled Multi-phase Field Model with Finite Interface Dissipation

A multi-phase field (MPF) model with finite interface dissipation proposed by Steinbach et al. is applied to simulate the dendritic solidification in Fe–Cr–Ni–Mo–C duplex stainless steel. This MPF model does not require an equal diffusion potential assumption and can take into account a substantial non-equilibrium interfacial condition. We develop the MPF code to couple with the CALPHAD thermodynamic database to simulate two-dimensional microstructure evolutions in multi-component alloys using the TQ-interface of Thermo-Calc. The message passing interface parallelization technique is adapted to the program code development to reduce computational elapse time. Solidification calculations were performed in two cases of quinary compositions: Fe–16Cr–2Mo–10Ni–0.08C and Fe–17Cr–2Mo–9Ni–0.08C. We confirm that the developed MPF method can be highly applicable to microstructure evolution simulation of the engineering metal alloy solidification.

New Gas Flow System for Long-Tape Reaction Tube of TFA-MOD Process

A multi-turning Reel-to-Reel tape conveyance system of the long YBCO coated conductors using TFA-MOD process is desired to be high production rate without large degradation between tape lines. The numerical simulation, which calculated the YBCO growth kinetics, gas element diffusion and gas flow, shown a possibility that the vertical gas flow onto the tape surface realized high production rate of YBCO conductor even on the wider tape. This possibility was also proved by experimental measurements.

Volume fraction dependence on coarsening of Y2BaCuO5 particles in Ba-Cu-O melt

The effect of the volume fraction of the solid phase (Vf) on coarseningphenomena of Y 2BaCuO5 (Y211) particles in Ba–Cu–O melt has been experimentally investigated. The rate constant of the coarsening cubic-law (K) also depends strongly on Vf and is classified into two groups. The samples with Vf lower than 15% reveal higher coarsening rate constants than those with Vf higher than 20%. The coarsening properties of the lower Vf were in good agreement with the classical mean field (MF) model that considered the effect of Vf. It was clarified that K values of the higher Vf were suitable for those calculated numerically by the communicatingneighbor (CN) model, in which the solute was assumed to diffuse directly amongthe particles. Thus, the coarseningphenomena of Y211 particles have been qualitatively explained by the difference in coarseningmechanisms as the MF and CN models. r 2001 Elsevier Science B.V. All rights reserved.