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.

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Effects of relaxation on glass transition and crystallization of ZrTiCuNiBe bulk metallic glass

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.

The microstructure and its evolution of a Zr 41 Ti 14 Cu 12.5 Ni 10 Be 22.5 bulk metallic glass ͑BMG͒ annealed under high pressure and below glass transition temperature are investigated by using high resolution transmission electron microscope, differential scanning calorimeter, x-ray diffraction, ultrasonic study, and density measurements. It is found that high pressure annealing below T g results in a microstructural transformation from short-range order to medium-range order in the BMG; the BMG with medium-range order structure exhibits different structural, thermal and acoustic properties.Recently, a new family of multicomponent glass-forming alloys such as La-Al-Ni, Zr-Ni-Al-Cu, and Zr-Ti-Cu-Ni-Be has been discovered which exhibits extraordinary glass forming ability ͑GFA͒ and properties. 1,2 The alloys require no special processing treatments, and fully metallic glass in greater bulk can be obtained. When heated through the glass transition, the bulk metallic glasses ͑BMG's͒ yield a supercooled liquid state of unusual stability for metals. The stability of the supercooled liquid in large temperature region, and the larger geometric size of the BMG have permitted far more extensive structural and properties investigations upon temperature and pressure than possible previously. There seems to be general agreement in that the basic process induced by annealing below glass transition temperature, T g is the structural relaxation, 3,4 but it is not clear to what extent this leads to structural units and what phenomena will happen when annealed under high pressure below T g . The structural relaxation is found to have significant effects on the microstructure, thermal stability, physical properties and subsequent crystallization, 5,6 but the cause for the effects is still unknown. The detailed knowledge of the atomic structure is essential to understand the special properties of the BMG. In this report, the local microstructural change of a Zr 41 Ti 14 Cu 12.5 Ni 10 Be 22.5 BMG induced by high pressure annealing below T g is studied. The ultrasonic study, density measurement, high-resolution transmission electron microscope ͑HRTEM͒, differential scanning calorimeter ͑DSC͒, and x-ray diffraction ͑XRD͒ are used to monitor the microstructural and properties changes.Ingots with a nominal composition of Zr 41 Ti 14 Cu 12.5 Ni 10 Be 22.5 were prepared by melting a mixture of elements in Ti-gettered arc furnace, and remelted in a vacuum-sealed quartz tube, and then quenched in water to get rod with a diameter of 12 mm. The details of the experimental procedure can be seen in Ref. 7. The amorphous nature as well as the homogeneity of the rod was ascertained with XRD, transmission electron microscope ͑TEM͒, small angle neutron scattering and reduced density function analyses. 5-7 The rod was machined down to 8 mm in diameter, by grinding off the outer surface, any possible oxide materials from the quartz tube container were removed. The composition carefully checked by chemical analysis. XRD was performed using a MAC M03...