D.Q. Zhao

Magnetocaloric effect in Gd-based bulk metallic glasses

Magnetocaloric effect and refrigerant capacity of Gd-based Gd53Al24Co20Zr3 and Gd33Er22Al25Co20 bulk metallic glasses are investigated. It is found that the magnetic entropy changes compare favorably with that of Gd and are slightly larger than that of the known crystalline magnetic refrigerant compound Gd5Si2Ge1.9Fe0.1. Their good refrigerant efficiency combining with high electrical resistivity, high thermal stability, outstanding mechanical properties, tunable nature, and sufficiently soft magnetic property make them an attractive candidate for magnetic refrigerants in the temperature range of 10–100K.

A highly glass-forming alloy with low glass transition temperature

A rare-earth Pr-based bulk metallic glass (BMG) is obtained in the shape of rod up to 5 mm in diameter by die cast. Unlike other rare-earth-based BMGs, it exhibits a distinct glass transition, the low glass transition temperature (Tg=409 K), a large and stable supercooled liquid region, and paramagnetic property. The glass transition as well as its kinetic nature and the fragility parameters of the BMG have been studied. The BMG offers an ideal model to investigate the nature of glass transition as well as the relaxation and nucleation with a large experimentally accessible time and temperature window at low temperatures.

Nanocrystallization of ZrTiCuNiBeC bulk metallic glass under high pressure

Nanocrystallization of Zr41Ti14Cu12.5Ni9Be22.5C1 bulk metallic glass (BMG) under high pressure is investigated. It is found that the nanocrystallization is pressure assisted, and the primary nanocrystallization temperature decreases as the applied pressure increases. Pressure annealing of the BMG in the supercooled liquid region produces a composite with dispersion of very fine nanocrystallites in the amorphous matrix. A fully nanocrystallization is obtained by pressure annealing under 6 GPa at 723 K. The pressure also controls the phase selection during the crystallization. The mechanism for the pressure-assisted nanocrystallization is discussed.

Magnetocaloric effect of Ho-, Dy-, and Er-based bulk metallic glasses in helium and hydrogen liquefaction temperature range

The authors study the magnetocaloric effect and refrigerant capacity of Ho30Y26Al24Co20, Dy50Gd7Al23Co20, and Er50Al24Co20Y6 bulk metallic glasses. Their magnetic entropy changes associated with spin glass to paramagnetic transition are larger than those of Gd, Gd5Si2Ge1.9Fe0.1, and many other intermetallic compounds reported in the same temperature range. The good refrigerant efficiency combined with their high electrical resistivity, high thermal stability, outstanding mechanical properties, and tunable nature makes these glassy materials be attractive candidates for magnetic refrigerants in helium and hydrogen liquefaction temperature range of 2–50K.

Elastic constants and their pressure dependence of Zr41Ti14Cu12.5Ni9Be22.5C1 bulk metallic glass

The acoustic velocities and their pressure dependence of bulk Zr41Ti14Cu12.5Ni9Be22.5C1 metallic glass (MG) have been measured up to 0.5 GPa by using a pulse echo overlap method. The elastic constants and thermodynamic parameters as well as their pressure dependence of the MG have been determined. The obtained elastic constants were compared to that of other kinds of glasses. More information about the microstructure, elastic properties, and glass forming ability of the MG was obtained.

Evolution of nanoscale morphology on fracture surface of brittle metallic glass

The authors report the observations of periodic morphology evolution on fracture surface of a brittle metallic glassy ribbon, suggesting a wavy local stress intensity factor along the crack propagation. The authors find that the formation of nanoscale damage cavity structure is a common characteristic morphology on the fracture surfaces. On the surface of the hackle zone, these cavities assemble and generate the nanoscale swirling periodic corrugations. The elastic waves interfering with the plastic process zone on the crack front is proposed to explain such dynamic crack instability. The authors’ observations support the notion of an impinging effect of elastic waves on propagating crack front.

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.

Stability of ZrTiCuNiBe bulk metallic glass upon isothermal annealing near the glass transition temperature

The stability of Zr41Ti14Cu12.5Ni10Be22.5 bulk metallic glass (BMG) upon isothermal annealing near the glass transition temperature has been investigated by using x-ray diffraction, differential scanning calorimetry, and the pulse echo overlap method. The density, elastic constants, and thermodynamic parameters as well as their annealing time dependence have been determined. The microstructural and properties changes of the annealed BMG were checked by acoustic measurement. Obvious structural and property changes were observed with prolonged annealing of the BMG near the glass transition temperature.

Formation and properties of new heavy rare-earth-based bulk metallic glasses

Abstract A series of new families of heavy rare-earth (RE) based bulk metallic glasses (BMGs) with excellent glass-forming ability and high thermal stability have been obtained by a copper mold casting method. Compared with the light RE-based BMGs, the heavy RE-based BMGs have much higher glass transition and crystallization temperatures and higher elastic moduli. It is found that the thermal stability is closely correlated with the elastic constants in the RE-based BMGs. The correlations found are useful for guiding BMG-forming alloy design to enhance stability.

Critical and slow dynamics in a bulk metallic glass exhibiting strong random magnetic anisotropy

The nature of the magnetic state of strong random magnetic anisotropy (RMA) remains elusive. It is unclear whether the RMA and the Ising spin glass systems belong to the same class or not. Here, we demonstrate, by investigations of the static, critical, and slow dynamic properties of a Dy-base bulk metallic glass (BMG), the RMA can be classified to a universal class of glass different from Ising spin glass. The results have implication for understanding the connection between RMA and spin glass and the subtle role of anisotropy in the magnetic transition of disorder and frustrated systems. On the other hand, our study has the significance in developing efficient BMGs for functional applications.