Deqian Zhao

Role of addition in formation and properties of Zr-based bulk metallic glasses

Bulk Nd-Al-Fe-Co glassy alloys with diameter up to 5 mm were investigated by magnetic measurements, magnetic force microscopy (MFM) and high resolution electron microscopy (HREM) at room temperature. The results from the measurement of vibrating sample magnetometer show that these samples with compositions Nd65Al10Fe25-xCox, (x = 0-10 at.%) and Nd60Al10- Fe20Co10 display hard magnetic properties with H-C of similar to300 kAm(-1), Ms of similar to 10 Am-2 kg(-1), and M-r of similar to 7 Am-2 kg(-1). The MFM measurements of the Nd60Al10Fe20Co10 bulk metallic glass (BMG) reveal the existence of magnetic domains with a period of about 0.36 mum, and the ordered clusters with the averaged size of about 5 nm was observed by the HREM on the sample. The domain structure or cluster is believed to be associated with the appearance of hard-magnetic properties in this alloy system. The existence of the large-size domains demonstrates that magnetic moment of a great deal of ordered atomic clusters in the BMG has been aligned by exchange-coupling

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

Pressure-induced amorphization of ZrTiCuNiBe bulk glass-forming alloy

Zr41Ti14Cu12.5Ni10Be22.5 alloy can be cooled under high pressure (HP) to a bulky glassy state at very low cooling rates. The structure and properties of the bulk metallic glass (BMG) are investigated by differential scanning calorimetry, x-ray diffraction, ultrasonic study, and density measurements. The effects of pressure on the glass formation are discussed from the points of view of nucleation kinetics and thermodynamics. The BMG obtained under HP is in a high-density amorphous state that is different in structure and property from low-density amorphous phase quenched in water. Solidification under HP is a promising way not only for synthesizing BMGs with more densely packed structures and different properties, but also for understanding the glass formation mechanism.

Nucleation and growth in bulk metallic glass under high pressure investigated using in situ x-ray diffraction

The effects of pressure up to 8.3 GPa on nucleation and growth in a Zr57Nb5Cu15.5Ni12.5Al10 bulk glass-forming alloy during heating, isothermal annealing, and cooling processes are investigated using in situ x-ray diffraction with synchrotron radiation. The metallic glass shows markedly different crystallization behaviors for different heat treatments under high pressure. Heating under high pressure can stabilize the supercooled liquid state. Isothermal high pressure annealing leads to nanocrystallization. The glass forming ability of the alloy can be enhanced by high pressure during cooling process. The effects of pressure on the nucleation and growth are discussed based on the nucleation theory.

Tb nanocrystalline array assembled directly from alloy melt

A two-dimensional (2D) thin film composed of Tb nanocrystals with uniform orientations is fabricated directly from Tb65Fe25Al10 alloy melt upon quenching. The Tb nanocrystals with vertical height of 15–30 nm and lateral width of 10–20 nm are assembled in the nanocrystalline array on an amorphous substrate. The formation mechanism for the aligned Tb nanocrystals is discussed. The single-step formation method may provide a new and flexible alternative to fabricate nanostructured films or arrays used for submicron devices.

Crystallization of ZrTiCuNiBe bulk metallic glasses

Crystallization behavior and kinetics, and microstructural change of ZrTiCuNiBe bulk metallic glass (BMG) were systematically investigated in ambient, preannealed, addition, phase separation, and high pressure annealed conditions by means of differential scanning calorimetry (DSC), x-ray diffraction (XRD), neutron scattering, in situ synchrotron XRD, density and acoustic measurements. The effective activation energy of the crystallization of the BMGs was determined by Kissinger method. It was found that the crystallization as well as the apparent activation energy of the crystallization was sensitive to the external conditions. Pressure annealing in the supercooled liquid region produces a composite with dispersion of very fine nanocrystallites in the amorphous-matrix. The pressure also controls the phase selection during the crystallization. The glass forming ability of the glass forming alloys has been discussed in view of the crystallization kinetics.

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.

Kinetics of glass transition and crystallization in multicomponent bulk amorphous alloys

Differential scanning calorimeter (DSC) is used to investigate apparent activation energy of glass transition and crystallization of Zr-based bulk amorphous alloys by Kissinger equation under non-isothermal condition. It is shown that the glass transition behavior as well as crystallization reaction depends on the heating rate and has a characteristic of kinetic effects. After being isothermally annealed near glass transition temperature, the apparent activation energy of glass transition increases and the apparent activation energy of crystallization reaction decreases. However, the kinetic effects are independent of the pre-annealing.

Formation of Fe56Mn5Cr7-Mo12Er2C12B6 amorphous steel

The Fe48Cr15Mo14Er2C15B6 amorphous steel can hardly be used as an engineering material because of its extreme brittleness and very low iron content. By changing the composition of the nonmagnetic amorphous steel, and using the relation between the reduced glass transition temperatureTrg and the glass forming ability, a new amorphous Fe56Mn5Cr7Mo12Er2C12B6 alloy with good glass forming ability and high iron content was obtained. The diameter of the as-cast sample rod reached 8 mm. This new amorphous steel has lower manufacturing cost due to its high iron content, and thus it can have wider applications.

Ultrasonic attenuation in Zr41Ti14Cu12.5Ni10−xBe22.5Cx(x=0,1) bulk metallic glasses under high pressure

The pressure dependence of ultrasonic attenuation in Zr41Ti14Cu12.5Ni10−xBe22.5Cxu200a(x=0,1) bulk metallic glasses has been studied up to 0.5 GPa by using a pulse echo overlap method. The effect of carbon addition on the attenuation is also investigated. Some unique characteristics of the ultrasonic attenuation are found and compared with those of other glasses. The origin of the anomalous attenuation behavior is discussed.