Materials Science Forum Vols. 546-549

Abstract: A series of samples of Y1-xCaxBa2Cu3Oy (YCBCO) were synthesized with 0.05≤x≤0.3 and characterized by DC magnetization, X-ray diffraction (XRD), and Rietveld refinement. It was found that Ca replaces Y and Ba in YBa2Cu3Oy (YBCO) simultaneously, and the amount of Ca in the Y and Ba positions is estimated by the refinement，respectively. The experimental results showed that the structural changes had a close correlation with Tc. With careful analysis of the change of the Tc below and above x=0.2 and the changes of the bond lengths, such as Cu(2)-O(2) and Cu(2)-O(3), it is suggested that the Ca substitution for Y suppresses the Tc more strongly than that for Ba.

Abstract: Porous Ti51Ni(49-x)Mox (x=0, 0.7, 1.0, 1.2) shape memory alloys were successfully fabricated by the self-propagating high-temperature synthesis (SHS) method. The effect of Mo content on microstructures, transformation characteristics and compressive properties of porous TiNiMo alloys was investigated systemically. It has been found that Mo doping into porous TiNi alloys will induce R phase transformation. A small amount of Mo addition (0.7at.%) improves compressive properties of porous TiNiMo alloy due to Mo solution strengthening and the obvious ductile fracture is observed on the fracture photography. However, the compressive strength and compressive strain of porous TiNiMo alloys with excessive Mo content decrease sharply and the failure manner turned into brittle fracture mode, which results from a large amount of Ti2Ni and Ti4Ni2O phases precipitated at grain boundary. Porous Ti51Ni48.3Mo0.7 alloy with suitable transformation temperature and high compressive strength is very promising for use as biomaterial and damping material.

Abstract: The structure, magnetization and magnetostriction of Sm(Zn1-xTx) (T=Fe, Co) polycrystalline alloys were investigated by X-ray diffraction, vibrating sample magnetometer and standard strain gauge techniques. It is found that annealed SmZn1-xFex alloys show a single Sm(Zn,Fe) phase with the CsCl-type cubic structure when x≤0.2. SmZn1-xCox alloys are a single Sm(Zn,Co) phase when x≤0.15 and the Sm-rich phase appears when x>0.15. The Curie temperature for SmZn1-xFex alloys increases with increasing Fe content in the range of 0≤x≤0.2 and that of SmZn1-xCox alloys slowly does in the same composition range. When Fe is substituted for Zn in SmZn compound, the magnetization and magnetostriction increase with increasing the Fe content when x≤0.2 and when x≤0.1, respectively. The magnetostriction of Sm(Zn1-xCox) alloys increases with increasing the Co content under the magnetic field of 320 kA/m in the range of 0< x≤0.1.

Abstract: ZnO:Al(ZAO) thin film is a kind of transparent conductive functional material which has a potential application in the solar cell and Atom Oxygen resisting systems of spacecrafts. High performance ZAO thin films were prepared by reactive magnetron sputtering and then irradiated by γ-ray with different dose or rate of irradiation. The as-deposited sample and irradiated ones were characterized by X-ray Diffraction, Scanning Electron Microscopy and Hall-effect measurement to investigate the dependences of the structure, morphology and electrical properties of ZAO on the dose and rate of γ-ray irradiation. Measurement of Positron Annihilation Doppler-Broadening Spectroscopy was carried out to study the variation of the defects in ZAO thin films before and after irradiation. It is indicated that γ-ray will excite the carriers, which are electrons in ZAO. A high rate of γ-ray irradiation could slightly destroy the bonds of Zn-O and decrease the crystallinity, while the effect of low rate irradiation is similar to heat annealing and increase the crystallinity of ZAO thin films. γ-ray has no apparent influences on the negative vacancy defects in ZAO thin film.

Abstract: Co and Si were selected as substitutes to improve performance of TbDyFe giant magnetostrictive alloys for special purpose, respectively. The results showed that the Co-doped Tb0.36Dy0.64Fe2 alloys can possess giant magnetostriction over a wide temperature range from -80 to 100
. Optimum magnetostriction, high electrical resistivity and improved corrosion resistance was obtained in Tb0.3Dy0.7(Fe1-xSix)1.95 system. High performance grain-aligned rods with <110> preferred orientation have been successfully prepared by zone melting unidirectional solidification. This paper also presents the design and fabrication of Giant Magnetostrictive Actuator (GMA) for active vibration control with oriented TbDyFe rods. Experimental results showed that the GMA possesses good static and dynamic performance. Excellent damping effect, 20-30 dB under the frequency range from 10 Hz to 120 Hz was obtained.

Abstract: We have newly designed a metastable β Ti-Nb-Si based alloy with biocompatible alloying elements without containing toxic V or Al for orthodontic applications. Microstructures and pseudoelastic behavior of β Ti-Nb-Si alloys were investigated in order to correlate the pseudoelasticity and microstructure together with martensite transformation. Nb and Si alloying to the present alloy make β phase to be stable. It is found that metastable β phase is favorable to display pseudoelastic behavior than stable or unstable β phase. Optical microscope (OM) revealed that stress-induced martensitic transformation takes place during room temperature deformation in the present alloys. Within the alloys having β (bcc) phase studied the alloy with low content of Si appeared to exhibit a dominant behavior for stress-induced martensitic transformation than that with high content of Si. After recrystallization heat treatment pseudoelasticity of the present alloy appeared to be prominent. The pseudoelastic behavior of this alloy was correlated to the stress-induced martensite transformation. Pseudoelasticity of the present alloys is hindered by the development of {001}<110> rotated cube component.

Abstract: The bulk tiles of ceramic fibers reinforced aerogel were prepared from two reinforcements, evenly dispersed ceramic fibers and sintered tiles. It has been found that ceramic fiber-reinforced aerogels showed higher thermal conductivity than aerogel itself. Shrinkage of aerogels in chopped fiber reinforced aerogel composites showed similar tendency as pure aerogel during gelation, but the shrinkage was prohibited during supercritical drying. By contrary, in the case of sintered tile reinforced aerogel, shrinkage of aerogel was completely limited in both gelation and drying processes. Average of about 50% increase of compressive strengths of the sintered tile reinforced aerogel to sintered tiles were obtained with an average density increase of about 36%, their thermal conductivity depressed slightly.

Abstract: In this work, (Fe,Co)–Zr–B–Cu films have been deposited on glass and Si substrates by DC magnetron sputtering method. X-ray diffraction analysis was used to identify the structure of the films. A transmission electron microscope (TEM) was employed to observe the microstructure for the films. Magnetic properties at room temperature were investigated by a Vibrating Sample Magnetometer (VSM). It was obtained that the as-deposited films on glass and Si substrates were in an amorphous state. In addition, it has been found that the coercivity is dependent on film thicknesses.

Abstract: We report a systematic study of the thickness dependence of magnetic properties in carbon-incorporated Mn-Si films synthesized on a 4H-SiC(0001) homoepitaxial wafer by molecular beam epitaxy (MBE)
and an annealing method. Magnetization characteristics reveal a dual-phase characteristic in films with decreasing thickness. The anomalous Hall effect has been observed in the thicker film; however, the observed temperature dependence cannot be explained by traditional anomalous Hall effect theory. The temperature dependent resisitivity indicates the film has a metallic behavior.

Abstract: Large scale and highly ordered thermoelectric BixTe1-x (0.4 ≤ x ≤ 0.7) nanowire arrays were successfully fabricated by cathodic electrolysis into porous anodic alumina membrane (AAM) templates in aqueous solution. The structure of the nanowires was characterized by X-ray diffraction and selected-area electron diffraction (SAED). Field emission scanning electron microscopy (FE-SEM) and transmission electron microscopy (TEM) results show that the nanowires are smooth and uniform with the diameters of about 50 nm and lengths up to tens of micrometers. Energy dispersive spectroscopy (EDS) was used to check the exact stoichiometry of as-prepared samples. The results reveal that the atomic ratio between Bi and Te can be modulated effectively by controlling the concentration of the electrolyte solution. The synthesis of high quality BixTe1-x nanowires with controllable x is significant for optimizing the thermoelectric performance.