Hardness measurements and electron microscopic observations were made to study factors affecting the aging of Mg-Zn alloy and Mg-Zn-(Ag) alloys. In regard to the homogeneous and heterogeneous nucleation in these alloys, direct aging, twostep aging and strain aging were carried out, with the results summarized as follows:the nucleation rate largely depends on the quenching rate, the concentration of zinc and the small amount of silver (0.04wt%).(2) In the C-curves which were obtained by plotting the incubation time against the reciprocal of the absolute aging temperature, the nose or the lower part of it gives an optimum condition for the pre-aging. As regards the direct aging and the observations show that these phases preferentially precipitate on dislocations and fine structures such as twin boundary and sub-boundary.
of electrical resistivity and hardness measurements, the X-ray Debye-Scherrer method and electron-microscopic observations. From the kinematic point of view the aging sequences were analyzed using the C-curve obtained by plotting the logarithm of the incubation time as a function of the reciprocal of the absolute aging temperature.The results showed that the tion of G. P. zones.
High critical current densities (4250 A/mm2 at 5 T, 4.2 K, and 15 000 A/mm2 at 2 T, 4.2 K) were achieved by using an artificially designed pin structure composed of randomly oriented clusters of Nb/NbTi multilayer in a NbTi composite superconductor (with a round cross section). The maximum values were obtained when the Nb layer thickness was designed to be approximately twice the coherence length in NbTi, where the layer thickness is five to ten times thicker than that of the optimized α-Ti ribbon thickness in a conventional NbTi system.
The long conductor fabrication is one of key technologies to realize the High-Tc superconducting power cable. A 50-m long conductor was fabricated by helically winding the High-Tc superconducting tape onto a former with a winding machine. The conductor consisted of ten layers of Ag-sheathed Bi-2223 tape which had a high critical current density of 10,000 A/cmZ (at 77 K). AC losses and layer-bylayer current distribution were measured, feeding AC current of 100 to 2,000 Arms to the conductor cooled by LN2. The results showed that most of the current flowed in the outer layers where the impedance was low, and that AC losses were remarkably reduced by making the current distribution uniform.
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