Wang Wen-Kui

Compression behaviour and equation of state of Zr44.4Nb7Cu13.5Ni10.8Be24.3 bulk metallic glass up to 39 GPa

The compression of Zr44.4Nb7Cu13.5Ni10.8Be24.3 bulk metallic glass (BMG) is investigated at room temperature up to 39 GPa using {in situ} high-pressure energy dispersive x-ray diffraction with a synchrotron radiation source. The equation of state of the BMG is obtained by the calculation of the radial distribution function. Pressure-induced structural relaxation is exhibited. It is found that below about 6 GPa, the existence of excess free volume contributes to the rapid structural relaxation, which gives rise to rapid volumetric change, and the structural relaxation results in structural stiffness under higher pressure.

Isostructural Transition of MgB2 Under High Pressure

The high-pressure behaviour of the superconductor MgB2 with a hexagonal structure has been investigated by the in situ synchrotron radiation x-ray diffraction method under pressures up to 42.2 GPa in a diamond anvil cell. An abrupt decrease of about 7% in the unit cell volume of this material occurs in the pressure range of 26.3-30.2 GPa. A split of the Raman spectrum was also observed. The jump of the compression curve and Raman spectrum are ascribed to an isostructural transition in MgB2 at a pressure of 30.2 GPa.

120K SUPERCONDUCTING TRANSITION IN HOT-PRESSING BI-PB-SR-CA-CU-O SYSTEM

Abstract Superconducting critical transition with onset at 123K and zero resistance at 101K are obtained by hot pressing in the Bi-Pb-Sr-Ca-Cu-O system. A.C.χ measurements show that there are 85K superconducting phase except for 110K superconducting phase. This sample has been investigated by X-ray powder diffraction and SEM observation, the X-ray powder diffraction patterns of two main superconducting phase can be indexed in the forms of orthorhombic cells with lattice parameters a=5.420 A , b=5.447 A , c=30.845 A and a=5.420 A , b=5.447 A , c=36.884 A respectively. As expecting SEM experiment shows that a lower porosity was obtained in the hot pressed sample.

High-Pressure Annealing Effect on Glass Transformation Temperature of Zr41Ti14Cu12.5Ni10Be22.5 Bulk Metallic Glass

Zr41Ti14Cu12.5Ni10Be22.5 bulk metallic glasses (BMG) are annealed at a temperature of 603 K under ambient and high pressures in the range of 3−6 GPa. The effect of high pressure annealing on the nanocrystallization process of compressed specimens is investigated by x-ray diffraction, differential scanning calorimetry and transmission electron microscopy. Experimental results show that the grain size of the crystalline phase decreases with the increasing pressure. For the Zr41Ti14Cu12.5Ni10Be22.5 BMG annealing at 603 K in the pressure range of 0−6 GPa, the activation energy 159.68 kJ/mol and the activation volume ΔV* = 0.94 cm3/mol are determined. The mechanism for the effects of the high pressure on the nanocrystallization process of the BMG is discussed.

Effects of gravity field on glass forming ability in ZrTiCuNiBe alloy

The solidification and glass forming ability of Zr41Ti14Cu12.5Ni10Be22.5 bulk glassy forming alloy is investigated by Bridgman unidirectional solidification at different growth velocities under different gravity field orientations. Large differences in glass formation, undercooling and crystallization morphology on different solidification conditions have been found and discussed from the point of view of gravity induced convection. The results are useful for understanding the nucleation and growth in the melt and glass formation mechanism in the alloy.

Kinetics of the Glass Transition of the Zr41Ti14Cu12.5Ni10Be22.5 Alloy Solidified in a Drop Tube

Droplets of Zr41Ti14Cu12.5Ni10Be22.5 glass-forming alloy with different sizes are solidified in a drop tube containerless process. The glass transition temperature Tg of Zr41Ti14Cu12.5Ni10Be22.5 glassy spheres solidified with different cooling rates is investigated by using a differential scanning calorimeter. It was found that all the amorphous spheres show an increase of Tg with the heating rate. The glassy spheres have a unique value for the glass transition activation energy Eg = 435.50 kJ/mol, which is independent of cooling rate q. The insensitivity of Tg to q is interpreted by an extension of the free volume model for flow.

Structural relaxation of Pd39Ni10Cu30P21 bulk metallic glass under high pressure

The Pd39Ni10Cu30P21 bulk metallic glass is isothermally relaxed under various pressures. The degree of the structural relaxation is evaluated in terms of the enthalpy recovery behaviours involved in the irreversible glass transition processes by using a temperature-modulated differential scanning calorimetry technique. A roughly Linear increase of the recovery enthalpy is observed within the experimental pressure range fi-om 2.67 to 4.45 GPa, which reflects the release of the frozen-in enthalpy in the as-quenched glass with increasing relaxation pressure. The pressure dependence of the timescale of the enthalpy recovery processes is also exhibited.

@Amorphous Ni50Ti50 film formed by solid-state reaction

The solid-state reaction technique has been used to form the amorphous Ni50Ti50 film. The alternative layers were prepared by an electron beam evaporating apparatus. The amorphization was determined by means of x-ray diffraction and confirmed by DSC experiments.

AG/SI MULTILAYERS WITH NANOMETER SIZED PARTICLES OF SILVER DURING ANNEALING PROCESS

Thein situ low angle X-ray diffraction and transmission electron microscopy were used to monitor the interdiffusion characteristics as well as the microstructure in Ag/Si multilayers with modulated wavelength 7. 64 nm when annealing from 323 to 573 K. The interdiffusion mechanism of Ag/Si multilayers with immiscibility is different from that of other metal/Si multilayers which are miscible. Phase separation takes place at 323 K, then silicon atoms diffuse into silver sublayers through silver grain boundaries and separate silver sublayers into nanometer sized silver particles gradually at higher temperature. The mean size of silver particles is about 5 nm. The activation energy and frequency factor are determined to be 0.24 eV and 2.02 x−20m2/s, respectively.

HIGH PRESSURE SYNTHESIS OF HIGH Tc A15 Nb3Si

The A15 Nb3Si with a smaller lattice parameter (α=0.5093nm) has been synthesized from the amorphous Nb77Si23 alloy under high pressure by using Bridgman anvils apparatus. Superconductivity measurements showed that the A15 phase produced from Nb77Si23 has the highest TC (19.1K) among all that can be obtained from Nb-Si alloys.