Ming Xiang Pan

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.

Carbon-nanotube-reinforced Zr52.5Cu17.9Ni14.6Al10Ti5 bulk metallic glass composites

Carbon-nanotube (CNT) reinforced Zr-based bulk metallic glass composites are prepared by the conventional die cast method. A large amount of CNTs still keep their seamless cylindrical morphology in the glassy matrix, even though some CNTs react with Zr, resulting in the formation of ZrC phase. Investigation shows that the elastic moduli, Vicker’s hardness, density, and Debye temperature of the composite are markedly changed by introducing CNTs into the glass. Our results suggest that CNTs are promising materials for preparing reinforced, lightweight bulk metallic glass composites with improved mechanical and physical properties relative to the undoped glass.

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.

Anomalous thermal stability of Nd–Fe–Co–Al bulk metallic glass

The thermal stability of Nd60Fe20Co10Al10 bulk metallic glass (BMG) has been studied by differential scanning calorimetry (DSC), dynamic mechanical thermal analysis (DMTA), isochronal dilatation and compression tests. The results show that the glass transition of the BMG takes place quite gradually between about 460 and 650 K at a heating rate of 0.17 K/s. Several transformation processes are observed during continuous heating with the first crystallization process beginning at about 460 K, while massive crystallization takes place near the solidus temperature of the alloy. The positive heat of mixing between the two major constituents, Nd and Fe, and, consequently, a highly inhomogeneous composition of the attained amorphous phase are responsible for the anomalous thermal stability in this system

Structural evolution and property changes in Nd60Al10Fe20Co10 bulk metallic glass during crystallization

The structural evolution and property changes in Nd60Al10Fe20Co10 bulk metallic glass (BMG) upon crystallization are investigated by the ultrasonic method, x-ray diffraction, density measurement, and differential scanning calorimetry. The elastic constants and Debye temperature of the BMG are obtained as a function of annealing temperature. Anomalous changes in ultrasonic velocities, elastic constants, and density are observed between 600–750 K, corresponding to the formation of metastable phases as an intermediate product in the crystallization process. The changes in acoustic velocities, elastic constants, density, and Debye temperature of the BMG relative to its fully crystallized state are much smaller, compared with those of other known BMGs, the differences being attributed to the microstructural feature of the BMG.

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.

Glass transition behavior, crystallization kinetics, and microstructure change of Zr41Ti14Cu12.5Ni10Be22.5 bulk metallic glass under high pressure

Glass transition behavior, crystallization kinetics, and the microstructural change of Zr41Ti14Cu12.5Ni10Be22.5 bulk metallic glass (BMG) are studied in ambient, annealing, and high pressure conditions. Significant structural relaxation induced by preannealing and high pressure annealing has been observed in the BMG obtained with a low cooling rate. The experimental results indicate that the BMG contains a large amount of vacancy-like free volume. The relaxation results in the microstructural transformation from short-range order to medium-range order and significant effects on the subsequent glass transition and crystallization. The role of relaxation in the glass transition and the crystallization is phenomenologically explained.

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.