[en] Top-seeded powder melting process (TSPMP) is an effective melting processing technique for the preparation of high J_c bulk YBCO. The remarkable advantage of TSPMP is that it is very convenient to control the size and distribution of 211 particles within bulk YBCO. We observed the microstructure of TSPMP-YBCO sample and the mean size of 211 particles is about 500 nm and well distributed. The thickness of 123 planes is about 2 μm. The density of twins in line is about (1.2-1.6)x10⁴ cm^-1. We fabricated the YBCO bulk sample with dimensions of diameter 30 mmx15 mm in batch by the TSPMP process. The maximum levitation force was measured to be 85 N at 77 K in 0.5 T, by using diameter28 mmx30 mm NdFeB magnet

[en] The effects of CeO₂ adding on the reduction of Y-211 particle size and the oxygenation temperature on T_c have been studied. It is shown that the decrease of pre-sintering temperature is more effective than adding CeO₂ for the Y-211 particle size reduction. For bulk YBCO, the oxygenation temperature affects not only the critical temperature T_c and other superconducting property, but also its microstructure. Our results show the low oxygenation temperature is suitable for the oxygenation process of melt-textured bulk YBCO. If the oxygenation temperature is above 600 deg. C, the macrocrack will propagate

[en] In this study, the J_c value was improved considerably by optimization of heat treatment for Bi-2223 phase formation and the post-annealing for adjustment of non-superconducting phases. As a result, high critical current (I_c) of 110 A (77 K) has been obtained on Ag-alloy sheathed multifilamentary tapes, the engineering critical current density (J_e) exceeded 10⁴ A/cm² (77 K). The Ag-alloy wires were successfully introduced into Bi-2223 core in each filament of multifilamentary tapes to improve the mechanical strength without degradation of J_c value

[en] The effects of Ti/TiN bi- and multilayered films on the fatigue performance of the Ti46Al8Nb alloy were investigated. Ti/TiN films with a total thickness of 1 μm were deposited on the Ti46Al8Nb alloy substrate by the hollow cathode deposition method. The samples were examined with various analytical techniques including nanoindentation, scratch test, stripping layer substrate curvature test and scanning electron microscopy. The results show that multilayered Ti/TiN films can enhance the fatigue strength of the Ti46Al8Nb alloy, whereas bilayered films have no obvious effect. Compared with the bilayer, the multilayer exhibits higher hardness, higher residual compressive stress and higher adhesion strength to the substrate. It is also demonstrated that the multilayer is responsible for retarding fatigue crack growth. All the superior properties make the hard Ti/TiN multilayer to be an effective protection coating for the enhanced fatigue strength of the brittle substrate.

[en] The heat-treatment parameters of both the calcination and the reaction heat treatment play a crucial role in the achievement of high quality (Bi,Pb)-2223/Ag tapes. The melting process has been successfully used for the processing (Bi,Pb)-2212 in order to achieve good grain alignment and connection. In this paper, we report the partial-melting process to fabrication of (Bi,Pb)-2223/Ag tapes and discuss the results of the effects of the partial-melting treatment on microstructure and phase development. The results indicated that the tapes prepared by partial-melting process exhibit higher grain packing density and better texture than those prepared by the normal process. As a result, the critical current density is improved

[en] The phase assemblage of precursor powder was controlled by changing the calcination temperature from 830 to 860 deg. C. The microstructure and the critical current density of tapes were strongly dependent on the phase composition of the precursor powder. SEM analysis shows that large needles of 2212 with an angle of 30 deg. were formed in the tape using the precursor powder calcined at 845 deg. C for 12 h. Some larger size CuO grains were presented in the tape with lower J_c value. Some secondary phases come from the precursor powder. It is important to obtain a reasonable phase composition in the precursor powder for the tapes with a good microstructure and high J_c

[en] In this work, the phase assemblage of the precursor powder, especially the Ca₂PbO₄ phase, was changed by adjusting the powder calcination temperature and the correlation between the properties of precursor powder and the heat treatment process of tapes, as well as the critical current has been analyzed. It was found that the tape heat treatment temperature has close relations with the content of the Ca₂PbO₄ phase in the precursor powders. The optimum heat treatment temperature of the tape increases dramatically and the tape sintering processing window is enhanced when the relative content of Ca₂PbO₄ phase decreasing in the precursor powders

[en] Bi-2223/Ag tapes with nominal chemical compositions of Bi_1.8Pb_0.4Sr₂Ca_2.2Cu_3-xNi_xO_y (x=0, 0.003 and 0.005) were prepared by powder-in-tube method. The XRD and SEM analysis of their phases and microstructures show that a proper amount of Ni doping at Cu sites does not impede the formation of Bi-2223 phase. The measurements of magnetic field dependence of critical current density J_c and resistance transition broadening under magnetic fields oriented along c-axis indicate that the Ni doping at Cu site can improve the flux-pinning ability of Bi-2223/Ag tapes significantly. The improvement of flux pinning is suggested to originate from the introduction of flux pinning centers due to the destruction of local superconductivity caused by Ni doping at Cu sites because of the ferromagnetism of Ni

[en] Microstructures and phase compositions of as-cast and extruded ZK60-xDy (x = 0-5) alloys were analysed by optical microscope, scanning electron microscope, X-ray diffraction and differential scanning calorimetry. Meanwhile, the tensile mechanical property was tested. With increasing Dy content, Mg-Zn-Dy new phase increases gradually, while MgZn₂ phase decreases gradually to disappear. As-cast microstructure is refined gradually; mean-while extruded one is refined further with decreasing average grain size to 1 μm for ZK60-4.32Dy alloy. Second phase, tending to distribute along grain boundary by continuous network in as-cast state, breaks and distributes dispersedly in extrusion state. As-cast tensile mechanical property remains almost unchanged at ambient temperature; however, extruded ones are enhanced significantly at ambient and elevated temperatures, respectively. Tensile strength at 298 and 473 K increases gradually from 355 and 120 MPa for ZK60 alloy to 395 and 171 MPa for ZK60-4.32Dy alloy, respectively. Extruded tensile fractures exhibit a typical character of ductile fracture. (author)

[en] Effects of grain-domain-size (GDS) on levitation force have been directly investigated and identified in well-textured YBCO bulks. A single-grain-domain YBCO bulk (φ=30 mm) was prepared by a top seeded melt growth process, then divided into two, three and four grain-domain to acquire the levitation forces of samples with different GDS. It is found that the levitation force of the samples monotonously decreases with the decreasing of the average GDS (or with the increasing of the total length grain-boundaries of the sample). The maximum levitation force for the single-grain-domain sample is about 1.68, 2.05 and 2.4 times higher than that of the samples with two, three, and four grain-domains. It is concluded that the levitation force of a single-grain-domain YBCO bulk is higher than that of samples with multi-grain-domains. It is also found that the levitation force is proportional to the average grain-domain radius, but inverse proportional to the total length of grain-boundaries of the sample, a simple physical model has been provided and well interpret the experiment results. (author)