De Qian Zhao

Super Plastic Bulk Metallic Glasses at Room Temperature

In contrast to the poor plasticity that is usually observed in bulk metallic glasses, super plasticity is achieved at room temperature in ZrCuNiAl synthesized through the appropriate choice of its composition by controlling elastic moduli. Microstructures analysis indicates that the super plastic bulk metallic glasses are composed of hard regions surrounded by soft regions, which enable the glasses to undergo true strain of more than 160%. This finding is suggestive of a solution to the problem of brittleness in, and has implications for understanding the deformation mechanism of, metallic glasses.

Relaxation of metallic Zr46.75Ti8.25Cu7.5Ni10Be27.5 bulk glass-forming supercooled liquid

The mechanical relaxation of metallic Zr46.75Ti8.25Cu7.5Ni10Be27.5 supercooled liquid has been measured by dynamic mechanical analysis. The relaxation behaviors are found to fit well the Kohlrausch–Williams–Watts equation in time domain as well as the Havriliak–Negami equation in frequency domain. Characteristic quantities relaxation time and time–temperature superposition are among the properties also exhibited. The metallic supercooled liquid is found to have common relaxation characteristics of the nonmetallic glass-forming supercooled liquids, demonstrating a connection of the underlying physics for quite different classes of glass formers.

Nd65Al10Fe25−xCox (x=0,5,10) bulk metallic glasses with wide supercooled liquid regions

Bulk metallic glasses of Nd65Al10Fe25-xCox (x=0,5,10) have been prepared in the form of 3 mm diam rods. Results of differential scanning calrimetry, dynamic mechanical thermal analysis (DMTA), and x-ray diffraction are presented for these alloys. It is shown that the glass transition and crystallization have been observed by DMTA. The reduced glass transition temperature of these glasses, defined as the ratio between the glass transition temperature T-g and the melting temperature T-l is in the range from 0.55 to 0.62. All these glasses have a large supercooled liquid region (SLR), ranging from 80 to 130 K. The high value of reduced glass transition temperature and wide SLR agree with their good glass formation ability.

Synthesis of Fe-based bulk metallic glasses with low purity materials by multi-metalloids addition

Abstract Bulk metallic glasses (BMGs) Fe 61 Co 7 Zr 10 Mo 5 W 2 M (15+ X ) ( X =0, 0.15, 0.30, 0.45, 0.60, 0.75 and 1.2) (M contains B, Al, Si, C and P) were prepared with low purity of raw materials by copper mould cast. X-ray diffraction and differential thermal analyzer results show that the glass forming ability (GFA) as well as the thermal stability of the Fe-based alloy made from low purity raw materials can be much improved by adding small amount of multi-metalloids. The positive effect of metalloids addition on the formation of the bulk metallic glasses is discussed.

Equation of state of bulk metallic glasses studied by an ultrasonic method

The acoustic velocities and their pressure dependence of various Zr- and Pd-based bulk metallic glasses (BMGs) have been measured by using a pulse echo overlap method. The elastic constants as well as their pressure dependence of the BMGs have been determined, and the equation of state of these BMGs was obtained and compared to that of other glasses and crystalline solids. The structural characteristic of the BMGs is discussed.

Excellent ultrasonic absorption ability of carbon-nanotube-reinforced bulk metallic glass composites

Zr52.5Cu17.9Ni14.6Al10Ti5 bulk metallic glass composites (BMGCs) containing carbon nanotubes (CNTs) are found to have a strong ultrasonic wave absorption ability. Ultrasonic attenuation coefficients of Zr-based BMGCs increase dramatically with increasing volume fraction of CNTs. The excellent ultrasonic wave absorption ability is attributed mainly to the multiscattering caused by the CNTs and ZrC phase dispersing randomly in the glass matrix.

Elastic behaviour and microstructural characteristics of Nd60Al10Fe20Co10 bulk metallic glass investigated by ultrasonic measurement under pressure

An ultrasonic pulse-echo method was used to measure the transit time of longitudinal and transverse (10 MHz) elastic waves in a Nd60Al10Fe20Co10 bulk metallic glass (BMG). The measurements were carried out under hydrostatic pressure up to 0.5 GPa at room temperature. On the basis of experimental data for the sound velocities and density, the elastic moduli and Debye temperature of the BMG were derived as a function of pressure. Murnaghans equation of state is obtained. The normal behaviour of the positive pressure dependence of the ultrasonic velocities was observed for this glass. Moreover, the compression curve, the elastic constants, and the Debye temperature of the BMG are calculated on the basis of the similarity between their physical properties in the glassy state and those in corresponding crystalline state. These results confirm qualitatively the theoretical predictions concerning the features of the microstructure and interatomic bonding in the Nd60Al10Fe20Co10 BMG.

Formation and crystallization of CuZrHfTi bulk metallic glass under ambient and high pressures

The formation of CuZrHfTi bulk metallic glasses (BMGs) and the crystallization of the typical Cu60Zr20Hf10Ti10 BMG under ambient conditions and high pressure have been investigated by differential scanning calorimetry, x-ray diffraction (XRD) and in situ synchrotron radiation XRD. The effects of high pressure on crystallization and formation of the CuZrHfTi alloy are discussed. The Kauzmann temperature, TK, where the entropy of the undercooled liquid equals that of the crystal, is also determined to be 724 K. The TK is compared with the experimentally observed rate-dependent glass transition, Tg. The kinetic study of the crystallization shows that the Cu-based BMG has much larger activation energies obtained using Kissinger analysis and is markedly different in crystallization kinetic behaviour compared to that of other BMGs with better glass forming abilities. An apparent correlation between crystallization temperature and activation energy is found in various metallic glasses. The correlation is discussed and connected with the thermal stability of metallic glasses.

Phase transition of Zr41Ti14Cu12.5Ni10Be22.5 bulk amorphous below glass transition temperature under high pressure

The effect of high pressure annealing on phase transition of the Zr41Ti14Cu12.5Ni10Be22.5 bulk metallic glass (BMG) is studied on compressed specimens by x-ray diffraction and differential scanning calorimetry (DSC) after annealing treatments at 573 K and under pressures up to 6 GPa. The results of DSC and transmission electron microscope show that the high pressure annealing cannot only promote structural relaxation, but also induce the occurrence of a phase transition at a temperature below the glass transition temperature in the BMG. The role of pressure on structural relaxation and phase transition is discussed.

Phase evolution and its effect on magnetic properties of Nd60Al10Fe20Co10 bulk metallic glass

The thermal stability of nanocrystalline clusters, the phase evolution, and their effects on magnetic properties were studied for as-cast Nd60Al10Fe20Co10 alloy using differential scanning calorimetry curves, x-ray diffraction patterns, scanning electron microscopy, and high-resolution transition electron microscopy. Thermomagnetic curves and hysteresis loops of the bulk metallic glass were measured during the annealing process. The high thermostability of the hard magnetic properties of the samples observed is attributed to the stability of the nanocrystalline clusters upon annealing, while the slight enhancement in the magnetization is due to the precipitation of some Nd-rich metastable phases. The mechanism of thermostability of the nanocrystalline clusters and the formation of the metastable phases are discussed.