Ping Wen

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.

Evolution of structural and dynamic heterogeneities and activation energy distribution of deformation units in metallic glass

We present experimental results on the distribution and evolution of energy barriers of deformation units in metallic glass (MG) via an activation-relaxation method. Our results show that the dynamical heterogeneity of metallic glass arises from its structural inhomogeneity, and there exist the close correlations between the deformation units, dynamical and structural heterogeneities, and relaxation behaviors in metallic glasses. The results might provide insights on the heterogeneities, plastic deformation, and relaxations behaviors of metallic glass.

Relationship between glass transition temperature and Debye temperature in bulk metallic glasses

The Debye temperature and glass transition temperature of a variety of bulk metallic glasses (BMGs) were determined by acoustic measurement and differential scanning calorimetry, respectively. The relationship between the Debye temperature and glass transition temperature of these BMGs was analyzed, and their observed correlation was interpreted in terms of the characteristics of the glass transition in BMGs.

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.

Formation and properties of Zr48Nb8Fe8Cu12Be24 bulk metallic glass

The spin-s quantum Heisenberg ferromagnetic model is investigated in the physical magnon theory. The effect of the extra unphysical magnon states on every site is completely removed in the magnon Hamiltonian and during approximation procedure so that the condition = 0(n greater than or equal to 2s + 1) is rigorously satisfied. The physical multi-approximation occupancy (1 less than or equal to n less than or equal to 2s) is proportional to T-3n/2 at low temperature and is equivalent to 1/(2s + 1) at the Curie temperature. The magnetization not only unified but also well-behaved from zero temperature to Curie temperature is obtained in the framework of the magnon theory for the spin-s quantum Heisenberg ferromagnetic model. The ill-behaved magnetizations at high temperature in earlier magnon theories are completely corrected. The relation of magnon (spin wave) theory with spin-operator decoupling theory is clearly understood

Observation of secondary relaxation in a fragile Pd40Ni10Cu30P20 bulk metallic glass

The dynamic elastic moduli in the temperature domain of a Pd40Ni10Cu30P20 bulk metallic glass were measured with dynamic mechanical spectroscopy at frequencies less than 100Hz. The primary relaxation is characterized by a single loss modulus peak and a rapid drop of storage modulus in the metallic supercooled liquid region. Below the conventional glass transition temperature, a pronounced shoulder in the loss modulus curves appears and the corresponding storage modulus decreases with increasing temperature. The phenomenon is common to glass formers of all types. The observations present the evidence of the existence of the slow β relaxation and affirm the universality of the separation of the primary and secondary relaxations in the supercooled liquid.

Internal friction behaviours in Zr57Al10Ni12.4Cu15.6Nb5 bulk metallic glass

The internal friction patterns of Zr57Al10Ni12.4Cu15.6Nb5 bulk metallic glass (BMG) were investigated with different frequencies and heating rates. An internal friction peak with extremely large magnitude is observed in the internal friction curves as a function of temperature (Q −1 –T curves). The internal friction peak was fitted by an equation Q −1 = AX(T )/η ,w hereA is a constant, X (T ) is the fraction of the glass/supercooled liquid and the viscosity η obeys the Vogel–Fulcher–Tammann relation. We confirm that the internal friction peak originates from both of the glass transition and crystallization. The anomalous behaviours of the peak suggest that Zr57Al10Ni12.4Cu15.6Nb5 BMG has a wide supercooled liquid region and the magnitude of the peak can be used to judge the glass forming ability (GFA) of the glass forming alloys. In addition, the internal friction technique proved to be a new powerful tool for studying structural relaxation and phase transition as well as the GFA of BMG.

The Grüneisen parameter for bulk amorphous materials

The longitudinal and shear velocities, and their pressure dependences, for various bulk amorphous materials, including bulk metallic glasses and non-metallic glasses, have been measured by the ultrasonic pulse echo overlap method under hydrostatic pressure (maximum: 2 GPa) or uniaxial compression in ambient conditions. The second- or third-order elastic constants and the long-wavelength acoustic mode Gruneisen parameter are calculated. The results reveal that all metallic glasses have positive pressure dependences of both the longitudinal and shear velocities, while for most non-metallic glasses both the longitudinal and shear velocities decrease with increasing pressure. Thus, the Gruneisen parameters evaluated for the mean mode and shear mode for metallic glasses and non-metallic glasses have opposite signs. This indicates that the influences of the short-range-order structure and bonding, correlating closely with the atomic configurations in the various amorphous materials, play an important role in the properties determined by vibrational anharmonicity. The negative and positive Gruneisen parameters exhibit mode softening and stiffness under high pressure, respectively. The results also clearly demonstrate that the Gruneisen parameter is affected by the pressure derivative of the shear modulus, especially for non-metallic glasses.

The inquiry of liquids and glass transition by heat capacity

Reconsidering the intrinsic connection between simple liquids and the glass transition, we attempt to understand them with an explicit liquid model. Liquids are defined to the mixture composed of tiny particles restricted in non-identical potential energy wells, where translational motions of tiny particles in statistical equilibrium, as well as vibrations and rotations, are distinguished. The liquid model offers an opportunity to build up a quantitative correlation between heat capacity and the basic motions appearing in liquids. Agreements between theoretical prediction and experimental data on heat capacities of typical simple liquids are reached. A serial of experimental data confirm that the glass transition originates from the falling out-of-equilibrium of the translational motions in liquids. The work might provide a novel and intuitive way to uncover a shady corner of the mysterious liquids and the glass transition.

Characteristics of microstructure and glass transition of (Zr0.59Ti0.06Cu0.22Ni0.13)100−xAlx bulk metallic glasses

The glass transition and the microstructural characteristics of (Zr0.59Ti0.06Cu0.22Ni0.13)100−xAlx (10⩽x⩽16) bulk metallic glasses (BMG) are investigated as function of Al content. It is found that the Al content has strong effects on the glass transition, microstructure, and properties of the alloy. The marked increase of the Debye temperature and shear modulus with increasing Al content indicates that the different Al incorporations result in microstructural change in atomic short range of the BMG. The increase of the glass transition temperature with the increase Al content is consistent with the large variation of properties with increase of Al content. The change of the microstructure of the glass-forming alloy is responsible for the change of the properties.