L. L. Sun

Ultrasonic investigation of Pd39Ni10Cu30P21 bulk metallic glass upon crystallization

Acoustic velocities of Pd39Ni10Cu30P21 bulk metallic glass (BMG) are measured by an ultrasonic technique upon annealing. The elastic constants and the Debye temperature are obtained. A large softening of the transverse phonon is exhibited in the as-quenched BMG relative to its crystallized state. Upon crystallization, the shear modulus and the Debye temperature increase by ∼30% and ∼12%, respectively; however, the density increases by only ∼0.6%. Some anomalous acoustic and elastic behaviors are observed near the glass transition temperature and in the supercooled liquid region of the BMG. The anomalies are explained with regard to the structural changes.

Elastic constants of Pd39Ni10Cu30P21 bulk metallic glass under high pressure

The pressure-dependent acoustic velocities of a Pd39Ni10Cu30P21 bulk metallic glass (BMG) have been measured up to 0.5 GPa by using an ultrasonic technique with the pulse echo overlap method. The elastic constants, the Debye temperature, and their pressure dependence are obtained. The isothermal equation of state (EOS) of the BMG is established in terms of the Murnaghan form. The atomic configurations of the BMG are discussed by comparing the elastic constants and the EOS with those of its metallic component and of other amorphous materials.The pressure-dependent acoustic velocities of a Pd39Ni10Cu30P21 bulk metallic glass (BMG) have been measured up to 0.5 GPa by using an ultrasonic technique with the pulse echo overlap method. The elastic constants, the Debye temperature, and their pressure dependence are obtained. The isothermal equation of state (EOS) of the BMG is established in terms of the Murnaghan form. The atomic configurations of the BMG are discussed by comparing the elastic constants and the EOS with those of its metallic component and of other amorphous materials.

Synthesis of diamond from carbon nanotubes under high pressure and high temperature

The investigation on elemental carbon has long been of nanotubes to diamond at 4.5 GPa and 13008C using a considerable interest because of its great importance in six-anvil high pressure apparatus with the existence of both science and technology. One of the most outstanding NiMnCo catalyst. The detailed characterization conducted achievements which occurred in carbon science was the shows that carbon nanotubes transform to quasi-spherical synthesis of diamond under high-pressure–high-temperaonion-like structures first and then to diamond crystals. It ture (HPHT) conditions [1,2]. Now, man-made diamond is is different from the phase transformation behavior of commercially available and plays an indispensable role in graphite to diamond under high pressure and high temperamodern industry for abrasives, tool coatings, microelecture conditions. tronics, optics and other applications. Another important For the experiments presented here, multiwalled carbon advance in carbon science was the discovery of fullerenes nanotubes with diameters of 20–50 nm produced by and carbon nanotubes [3,4]. These novel carbon phases catalytic chemical vapor deposition (CCVD) were used as have gained high visibility because they have the potential starting material (Fig. 1). A 63600 ton six-anvil high to exhibit unique structural variety and extraordinary pressure apparatus with an electric current heating device optical, mechanical, and electronic properties [5]. Recentwas employed for the high pressure experiments. In each ly, a number of studies relating to the behaviors of experiment, about 50 mg of carbon nanotubes placed fullerenes under high pressure have been reported which between two NiMnCo alloy flakes were put into the high were focused on probing the cage structure stability and pressure cavity and a cubic body with a cylinder sample looking for new novel structures [6–8]. Moreover, it has chamber of pyrophyllite was used as pressure seal and been demonstrated that fullerenes can convert to diamond transmitting medium. Before and after high pressure runs, by applying high pressure at either room temperature [9] or the samples were monitored by transmission electron high temperature [10]. However, only a few works have microscopy (TEM; H8100), scanning electron microscopy been so far focused on the structural stability and phase (SEM; S-4200) and Raman spectroscopy (T64000). Hightransformation of carbon nanotubes at high pressure resolution transmission electron microscopy (HRTEM) [11,12]. As we know, the transformation of graphite or investigations were carried out using a JEOL2010 micrographite-like materials to diamond is of great technological scope operating at 200 kV. importance and therefore remains an exciting field in both Fig. 1 shows the representative morphology of carbon experimental and theoretical studies. Therefore, a detailed nanotubes in the starting material. The carbon nanotubes study of the behaviors of carbon nanotubes at high exhibit typical concentric graphitic shell structure with a pressure is very necessary for further understanding their hollow core. The diameters of most carbon nanotubes in structures and properties and comparing with that of our sample are around 30–40 nm uniformly. No other graphite. forms of carbon can be detected in the sample by TEM In the present work we report the conversion of carbon study.

Effects of buoyancy convection on phase morphology during solidification of Pd40Ni40P20 alloy

Samples of Pd40Ni40P20 alloy were solidified both on the ground and on board a Chinese Retrievable Satellite in order to study the effects of gravity-induced convection on the phase morphology. In comparison to the secondary dendritic spacing, the effective mass transport coefficient under normal gravity condition was estimated to be 1.95 times as high as that under microgravity conditions at the cooling rate of 0.056 K s(-1). The higher mass transport coefficient value due to the existence of buoyancy convection on the ground led to the formation of coarser dendrites of the primary phase Ni5P2 in the ground-based sample

Short-range structure of Zr41Ti14Cu12.5Ni10Be22.5 glass prepared by shock wave

Short-range structure of a Zr41Ti14Cu12.5Ni10Be22.5 bulk metallic glass prepared by shock-wave treatment was investigated by x-ray diffraction using synchrotron radiation with a wavelength of 0.112u200a71 A. The radial distribution function was obtained from S(Q) with a large Q value up to 20 A−1. The oscillation in S(Q) of the glass definitely persists up to Q∼14u2002A−1. The shoulder on the high Q side of the second peak is observed in the bulk glass. It is found that the glass has higher coordination numbers in the range of r∼2.4–5.6 A and lower numbers in the range of r∼5.6–9.5 A than those for a water-quenched glass while the shell distances are similar in both glasses prepared by shock-wave and water-quenching methods. In the shock-waved glass, atomic configurations in the first, fourth, or fifth coordination shells are modified, i.e., atoms are packed denser in the first two coordination shells and less (or more free volume) in the third and fourth coordination shells as compared to those for the water-que...

Solidification characteristics of Pd40Ni40P20 alloy under microgravity condition

The microstructure and solute distribution of Pd40Ni40P20 alloy solidified both on board a Chinese retrievable satellite (μg) and on the earth (1g) were studied. It was found that the dendritic primary phase formed under microgravity condition was finer and shorter. In the central area of the sample some asteroidal patterns of the primary phase were present in the microstructure. The primary spacing of the dendrites at the cooling rate of 0. 056 K/s was smaller than that measured in the ground-based experiments at the same cooling rate, but almost the same as that cooled at 0.67 K/s on the ground. With these experimental results, mass transport coefficients both in space and on the earth were evaluated.

Evaluation of effective mass transport coefficients through comparison of solidification on the ground and on board a satellite

Mass transport caused by buoyancy convection in front of the solid–liquid interface was evaluated in terms of measurements of primary dendritic spacing combining with separation of the effective (or integral) mass transport coefficient DL. It was shown that DL in normal gravity (1g) condition was 1.64 times as high as that in microgravity (μg) condition at the cooling rate (v) of 0.056 K/s for Pd40Ni40P20 alloy. The higher DL value is due to the contribution of buoyancy convection on the ground.

Compression behaviour of Pd39Ni10Cu30P21 bulk metallic glass up to 23.5 GPa

The compression behaviour of a Pd39Ni10Cu30P21 bulk metallic glass is investigated at room temperature up to 23.5 GPa using in situ high pressure energy dispersive x-ray diffraction with a synchrotron radiation source. Pressure induced structural relaxation of the bulk metallic glass is exhibited within the pressure range. It is found that below about 5 GPa, the existence of excess free volume contributes to rapid structural relaxation, which gives rise to rapid volumetric change. Under higher pressure, further relaxation results in structural stiffness.

Influence of buoyancy convection on solute distribution in Pd40Ni40P20 alloy

The differences in the solute distribution in microstructure of Pd40Ni40P20 alloy solidified on board a Chinese retrievable satellite and on the ground were studied. In comparison with those crystallized under normal gravity conditions (1 g), it was found that the P content was lower, but the Pd content was higher in the primary phase in microgravity conditions (μ g). In the eutectic region the P content, however, was increased but the Pd content was decreased. The differences in solute distribution crystallized under 1 g and μ g conditions show the influence of buoyancy convection on the mass transport coefficient in liquids under normal gravity conditions.

In situ detection of two-stage crystallization in ZrTiCuNiBe under high pressure and high temperature

Structural changes in bulk metallic Zr41.2Ti13.8Cu12.5Ni10Be22.5 glass subjected to heat treatments under high pressure were investigated by means of synchrotron radiation x-ray diffraction (SRXRD). In situ SRXRD measurements showed that the crystallization process of this material is comprised of two stages. Subsequent heating at 10 GPa converts the sample from the amorphous (Am) phase into a metastable fcc phase and then leads to the fcc phase changing back to the Am phase, indicating that there is a kind of reversible phase transition phenomenon occurring in the alloy. Such phenomenon is explained on the basis of free energy considerations.