Materials Science Forum Vols. 745-746

Abstract: The nearly stoichiometric Fe-Co alloy is well known as soft magnetic materials with high saturation magnetization and Curie temperature. However, the application is restricted by its brittleness and poor machinability. For this reason, we studied the rolling process of this alloy. Firstly, the effect of final thickness of hot rolling on the cold rolled samples showed that there was little difference for these cold rolled samples, and the thinner hot rolling samples were not so easy to crack during the cold rolling. Secondly, the soft magnetic properties were found to be better under the 1050 water quench when we studied the influence of different solution temperature on soft magnetic properties. Thirdly, with the increase of annealing time, grain size and soft magnetic properties of 1J22 alloy increased, whereas mechanical properties decreased.

Abstract: Sc₂O₃-doped zinc oxide varistor ceramics were prepared by a solid reaction route. The microstructure and the electrical properties was analyzed by scanning electron microscope and X-ray diffraction. Sintering time influences on the microstructure and the electrical properties of Sc₂O₃-doped zinc oxide varistor ceramics are studied. The results show that the electrical properties of Sc₂O₃-doped zinc oxide varistor ceramics sintered at 1000 and sintered for 1 h was better: the voltage gradient was 653 V/mm; the leakage current was 0.18 μA and the nonlinear coefficient was 57.1.

Abstract: In the process of BiFeO₃ film preparation by magnetron sputtering, Bi element is volatile, leading to the films which often appear impurity phases. Therefore, Both Bi excessive 5% (B_1.05FO) and 8% (B_1.08FO) BFO film in Si substrate were prepared by magnetron sputtering. X-Ray Diffraction (XRD) results showed that the BFO thin films fabricated in the Si substrate are perovskite structure, that the B_1.08FO film appeared less impurity phases than B_1.05FO film, and that stress due to substrate lattice mismatch caused the shift of XRD patterns. In Raman study, it was concluded that both B_1.08FO film and B_1.05FO film appeared ten Raman peaks in the range from 50cm^-1 to 800cm^-1, and that B_1.08FO Raman peaks intensity was stronger in 137.1cm^-1.168.5cm^-1 and 215.3cm^-1. Spectroscopic ellipsometry test showed that the refractive index and the extinction coefficient of B_1.05FO film were 2.25 and 0.07 respectively in 600 nm with 2.67eV of energy gap; the refractive index and the extinction coefficient of B_1.08FO film were 2.14 and 0.05 in 600 nm respectively with 2.71eV of energy gap. Atomic Force Microscope (AFM) was used to characterize the film surface morphology, finding that the B_1.08FO film prepared in Si substrate was denser while grain size and surface roughness were smaller.

Abstract: In this paper, Eu³⁺-doped LaAlO₃ powders which with the concentration of Eu³⁺ in the range of 0~5% were prepared by a new liquid mixing method. The structure of the LaAlO₃ powders were investigated by X-ray diffraction (XRD), and the influence of the increase of temperature on the crystal structure were also studied. We found that the powders crystallized above 800 which means higher temperature can improve the crystallization. The influences of the increasing Eu³⁺ concentration were also studied through the XRD patterns. The average sizes of the samples were also calculated by the Sherrer equation. The optical properties of different concentration of Eu³⁺-doped LaAlO₃ particles were investigated through the reflection spectra.

Abstract: In this paper, for the purpose of enhancement in the magnetic behavior, the five-layer Aurivillius phase structure Bi₆Fe_2-xCo_xTi₃O₁₈ (BFCT-x, x = 0.0 ~ 2.0) ceramics were synthesized using the solid-state reaction method from a mixture of Bi₂O₃, Co₂O₃, Fe₂O₃, and TiO₂ powders with different stoichiometric ratio. The microstructure, ferromagnetic and ferroelectric properties are investigated. The crystallographic structures of BFCT-x are determined to be the typical five-layer Aurivillius phase with a suggested structural transformation at heavy doping of Co ions. At room temperature, the remnant magnetization (2M_r) of BFCT-0.0, BFCT-0.6, BFCT-1.0 and BFCT-2.0 samples are 0.043 memu/g, 0.59 emu/g, 0.81 emu/g and 1.75 memu/g, respectively. The 2M_r, at first, gradually enhance and reach a greatest value of 0.81 emu/g at x = 1.0 then degrade again with the increasing of the ratio x. At room temperature, the samples have ferroelectricity, which the remnant polarization (2P_r) of the BFCT-0.0 , BFCT-0.6, BFCT-1.0 and BFCT-2.0 samples are 2.8 μC/cm², 8.0 μC/cm², 3.0 μC/cm² and 7.2 μC/cm² respectively. The 2P_r first increases, then decreases and increases again with Co doping. When x = 0.6, the 2P_r reaches a maximum value of 8.0 μC/cm².

Abstract: Giant magnetostrictive materials have a broad potential application in aviation and aerospace field owing to its good properties. The actuators made of the materials show excellent performance which makes them a good choice for precision positioning. This paper presents a micro-displacement positioning system of the giant magnetostrictive actuator (GMA). The structure of the system and its control method are described. In order to achieve the steady micro-positioning characteristics, the adjustment process of the system based on the control algorithm of Programmable Multi-axis Controller (PMAC) was researched. The response time of the GMA was less than 1 ms which was shown in the step response curve. Relatively large displacement (5~20 µm) positioning and micro-displacement (0.9~3 µm) positioning were achieved with the average positioning systematical errors of less than 0.5 µm.

Abstract: A device for measuring high-TC superconducting transition temperature in a small cryocooler is described which allows a samples temperature to fall steadily from room temperature to 45K. This cryocooler not only meets the high-TC superconductors measurement requirements, but also yields accurate measurement results under ambient conditions. In this device, two measurement methods for measuring high-TC superconducting transition temperature are applied: the electric transport and the AC susceptibility. The former adopts a four-wire method to eliminate the contact resistance between the leads and the sample. During the measurement process the current reversal method for datum processing is applied to eliminate the thermoelectric voltages; this ensures the repeatability error less than 0.4K in the measurement of the superconducting transition temperature. The AC susceptibility method adopts a lock-in amplifier to provide an AC voltage signal for the primary coil, and then lock-in amplifier is used to measure the electrical signals of the secondary coil according to the AC magnetic susceptibility values. The advantage of this device is that by merely changing the position of the sample in the vacuum chamber, the R-T curve and the χ-T curve of a superconducting sample in the same temperature range can be automatically recorded, which provides reliable data for high-TC superconductor transition curve measurement.

Abstract: Multi-filamentary Nb₃Sn strand for ITER has been successfully fabricated by a conventional internal-tin (IT) route at Western Superconducting Technologies, Co. Ltd. All the performances of the IT Nb₃Sn strand is able tomeet the ITER specifications. In 2010, one hundred kilograms of IT Nb₃Sn strand has been cabled, jacketed and integrated into conductor sample titled with TFCN2 by ASIPP in China and tested in CRPP, Switzerland. After 1200 cycles warm-up and cooling down, T_cs of the TFCN2 Sultan sample at 10.78 T, 4.5 K are 6.35 K for the left leg and 6.37 K for the right leg, respectively, which is larger than the ITER lower limit of 5.7 K. This is the first successful Sultan sample made of Chinese Nb₃Sn strand. In 2011, the influence of applied axial strain on critical current (I_c) was investigated using TFCN2 strand in the University of Twente, the Netherland. The irreversible degradation of I_c starts around +0.23% tensile intrinsic strain. The heat treatment influence of the duration at 650 °C on microstructure and performance was also studied. It was found that the fraction of un-reacted Nb after heat treatment is dependent on the position in the cross section. The hysteresis loss increases much faster than I_c when the duration at 650 °C increased.

Abstract: The annealing effects on the microstructure of Cu-Nb microcomposites fabricated by bundling and drawing process have been studied. During annealing at temperature as high as 800, the intensity of (110) diffraction peak of Nb became sharper and higher. The significant cylinderization and coarsening phenomenons of the niobium filaments were observed. The influence of microstructural changes on the hardness and the tensile strengths of Cu-Nb wires were discussed.

Abstract: The core breaking mechanism of the traditional Bi-2212 wires with filament configuration of 85×7 during the drawing process was analyzed, and the solution of these problems was given. The results showed that the major reason of core breaking occurs was that the tensile stress was bigger on the center than the edge of Bi-2212 wires during the drawing, and the silver-superconductor ratio was smaller of the center than the edge of the traditional Bi-2212 wires. It was effective to avoid the core breaking of Bi-2212 wires using the Ag core strengthener, and the uniformity of distortion of Bi-2212 wires during the drawing was improved, and the critical current of Bi-2212 wires increased 40% than that of traditional wires. If the diameter of the filament of Bi-2212 wires decreased further, there would be lots of bridging between core and core, which provided routeway for current. So the critical current of Bi-2212 wires was improved further.