Materials Science Forum Vols. 534-536

Abstract: Cube textured Ni substrate were fabricated for YBCO coated conductors from the initial specimens prepared by powder metallurgy (P/M) and casting and the effects of annealing temperature and reduction ratio on texture formation and microstructural evolutio were evaluated. The initial specimens were rolled by 98.6% and 99.2% reduction ratio and then annealed in the temperature range of 600°C to 1200°C. The microstructure and texture were evaluated by optical microscopy and X-ray pole-figure analysis. We observed that microstructure of the initial specimen varied with preparation methods.Texture analysis indicated that a strong cube texture formed for substrate made by P/M, and the degree of texture did not significantly vary with annealing temperature of 600°C~1100°C. On the other hand, the texture of substrate made by casting was more dependent on the annealing temperature and twin texture ({221}<221>) and several minor texture components started to form at 1000°C. In addition, the texture of substrate made by P/M was significantly dependent on the reduction ratio.

Abstract: Bi-2223/Ag tapes are usually used for superconducting power cables and magnets. Bi- 2223 ceramic superconducting core can be damaged under complicated stress and strain conditions such as winding tension, bending and twisting. In this study, we have presented the effect of axial stress and bending strain on the superconducting properties of Bi-2223/Ag tapes. In order to establish the value for 95% retained Ic of the Bi-2223/Ag tapes under various stress-strain conditions, the tension apparatus with bending former was used to apply the tension and bending stress-strain. Tension and bending stress-strain simultaneously applied to the tapes could reduce the critical current even though each applied stress and strain values were not higher than that of 95% retained Ic of the tapes. Complex stress-strain conditions including the thermal stress-strain have accelerated the degradation of the Bi-223/Ag tapes. The deformation temperature was important to maintain the 95% retained Ic of the Bi-2223/Ag tapes after bending or tension deformation because mechanical strength of the tapes can be changed drastically between room temperature and 77 K.

Abstract: The filling property of the binder treated iron based powder made of atomized iron powder was compared with that of the one made of reduced iron powder. The latter one showed a better filling property than the former one, although the original reduced powder showed a worse flow rate. Changing the particle size distribution of the original atomized powder from wide to narrow like the original reduced iron powder, improved the filling property of the binder treated powder. As a result, the particle size distribution of the original iron powder was found to strongly affect the filling property of the binder treated powder.

Abstract: Biomimetic apatite deposition behaviors and mechanical performance for as-rolled and annealed Ni-Ti plates were investigated. Apatite nucleation and growth on Ni-Ti in SBF (simulated body fluid) was not appreciably influenced by heat treatment. But, the apatite deposition rate increased slightly by NaOH surface treatment. The nodular apatite on the deposited layer is favored on a macro-scale since the surface energy of polycrystalline apatite particles can be reduced by forming nodules. The weight gain after apatite deposition for Ni-Ti (0.004 g/cm2) after 10 days were found to be smaller that that of NaOH treated Ti-6Al-4V, but it was comparable to that of non- NaOH-treated Ti-6Al-4V (0.004 g/cm2). The stress-strain responses of annealed Ni-Ti displayed the pseudoelastic behavior associated with stress-induced martensite formation with the transition stress for the martensite formation equal to 320 MPa. On the other hand the cold worked Ni-Ti displayed no appreciable pseudoelastic region and the yield stress was ~500MPa. A good biomimetic apatite formation and excellent mechanical performance of Ni-Ti suggests that Ni-Ti can be an excellent candidate material for orthopedic implants.

Abstract: For precise property control of sintered products, it is important to know the powder characteristics, especially the packing density of the powder. In a previous work, we developed a packing simulation program that could make a packed bed of spherical particles having particle size distribution. In order to predict the packing density of the actual powder that consisted of nonspherical particles, we combined the packing simulation with a particle shape analysis. We investigated the influence of the particle size distribution of the powder on the packing density by executing the packing simulation based on particle size distributions of the actual milled chromium powders. In addition, the influence of the particle shape of the actual powder on the packing density was quantitatively analyzed. A prediction of the packing density of the milled powder was attempted with an analytical expression between the particle shape of the powder and the packing simulation. The predicted packing densities were in good agreement with the actual data.

Abstract: Dry-bag CIP process has become a very popular method in the large volume production of powder compacts in the P/M and ceramic industries. Intensive technological research on the Drybag equipment has been carried out to improve the dimensional accuracy and the productivity. In this study, the rubber mold design technology with FEM simulation during pressing has been introduced, in order to achieve higher dimensional preciseness, and criteria for the selection of Drybag equipment, namely the In-line type or Off-line type, have been established based on the powder flowability index proposed by Carr. Based on these research results, high productivity Off-line Drybag CIP equipment, which can realize good dimensional accuracy with high productivity, was developed even for non granulated powders with poor packing density. This paper describes the research results and the present status of the most advanced Off-line Dry-bag CIP equipment technologies.