Yoshinari Kaieda

Fabrication of composition-controlled TiNi shape memory wire using combustion synthesis process and the influence of Ni content on phase transformation behavior

Abstract TiNi intermetallic compounds were manufactured on an industrial scale using a combustion synthesis process that exploits the heat of formation between Ti and Ni. In this paper we investigate the influence of Ni content on the phase transformation temperature. The TiNi shape memory intermetallic compounds manufactured are homogeneous, show no gravity segregation, and have low oxygen content. Hot and cold plastic working can be carried out without difficulty. The martensitic (Ms) transformation temperatures of specimens that were solution-treated and heat-treated for aging fall rapidly with increased Ni content. However, the transformation temperature bottoms out at 51.4 at.% Ni and begins to rise again at 51.7 at.% Ni. The reason why the Ms temperature, etc., of the specimens heat-treated for aging rise more than for solution-treated specimens is that the Ti3Ni4 precipitates, causing the Ni content of the matrix to fall. The pattern of change in transformation temperature as a function of Ni content in the present experiment agrees with other researchers’ data in spite of the combustion synthesis process fundamentally different from the conventional melting process.

Effect of Time of Heat Treatment on the Growth of Superconductive Phase of Bi-System Superconductor

The effect of the heat treating time is investigated to develop the fabrication technique of Bi system superconductor. A temperature just below the softening of the specimen is selected as a sintering temperature. The content of Pb additive is substituted for 20% of Bi. Various heating time and the growth of the superconducting phase are investigated. The measurements of the magnetic susceptibility, X-ray diffraction and SEM observation of the superconducting phase are carried out. From the results of the experiments to investigate the effect of heat treating time, the specimen with 300 hours of heat treatment time has most high Tc phase.

Effect of Cold Isostatic Pressing on Superconductivity of Y-Ba-Cu-O System

The effect of cold isostatic pressing in the forming process on superconductivity is studied in Y-Ba-Cu-O system ceramics. Y2O3, Ba(NO3)2 and CuO are mixed to the ratio of Y:Ba:Cu=1:2:3, calcined at 1173 K, mixed with and without the various amount of CuO as a binding additive, formed with cold isostatic press at various pressure and sintered at 1173 K. The critical temperature and the zero field critical current density at 77 K are measured. The values of Tc are almost same in all kinds of the specimens but the values of Jc are sensitive to the amount of a binding additive and the cold isostatic forming pressure.