Xiaohua Chen

A porous bulk metallic glass with unidirectional opening pores

Porous Zr-based bulk metallic glass (PMG) with unidirectional opening pores is prepared by electrochemical etching of tungsten wires of the W/bulk metallic glass (BMG) composites. The porosity and pore size can be controlled by adjusting the tungsten wires. The PMG showed no measurable loss in thermal stability as compared to the monolithic Zr-based BMG by water quenching and is more ductile and softer than the pore-free counterpart. The specific surface area of the PMGs is calculated to be 0.65, 3.96, and 10.54 m(2)/kg for 20, 60, and 80 vol % porosity, respectively. (c) 2007 The Electrochemical Society.

Effect of MgO/Co interface and Co/MgO interface on the spin dependent transport in perpendicular Co/Pt multilayers

Effect of the metal/oxide interface on spin-dependent transport properties in perpendicular [Co/Pt]3 multilayers was investigated. The saturation Hall resistivity (ρxy) is significantly increased by 45% with 1.4 nm thick CoO layer inserted at the top Co/MgO interface; whereas it is increased only 25% with 1 nm thick CoO layer at the bottom MgO/Co interface. The interfacial structures characterized by X-ray photoelectron spectroscopy show that the MgO/Co interface and Co/MgO interface including chemical states play a dominant role on spin-dependent transport, leading to different anomalous Hall behavior.

Calculations of potential functions and thermophysical behaviors for La62Al14Ni12Cu12 and Cu46Zr44Al7Y3 bulk metallic glasses

Bulk metallic glasses La62Al14Ni12Cu12 and Cu46Zr44Al7Y3 were prepared by copper mold suction casting. The thermal-physical behaviors of bulk metallic glasses were investigated by means of x-ray diffraction, differential scanning calorimetry, ultrasonic techniques, and dilatometry. By calculating the Mie potential function from experimental data, the values of potential function powers (m and n) and related physical parameters such as the mean binding energy, etc., are obtained. Thus, unlike what some people have done by assuming values of m−n (7–14), the values of average nearest-neighbor separation r0 and effective depth of pair potential ϕ0 can be obtained from calculated values of m and n from Mie potential functions and they agree very well with the results in the literature. The calculations can be well consistent with the thermophysical behaviors by comparing the two amorphous alloys. In addition, it was enhanced that the effective depth of pair potential correlated with the glass-forming ability o...

Bulk metallic glass rings prepared by a modified water quenching method

Abstract Bulk metallic glass rings have the potential applications as annular gasket and active solder in special fields. The bulk metallic glass ring of Zr41.2Ti13.8Cu12.5Ni10.0Be22.5 with the outer diameter, the inner diameter, and the thickness of 38, 36, and 5 mm, respectively, was prepared by using a special shaped quartz tube water quenching method. The mechanical properties along the whole cross section were investigated by a nanoindentation method, and no evident variation of the Youngs modulus and hardness was found, further indicating the single amorphous structure. Amorphous ring and tube-shape parts with different dimensions can be produced by this method.

Effect of Nb on the corrosion behavior of continuous bulk metallic glass-coated steel wire composites

Abstract(Zr41.2Ti13.8Cu12.5Ni10Be22.5)100−xNbx (at%, x=0 and 8) bulk metallic glasses (BMGs) were coated on the surface of Q195 steel wires by a continuous coating process. The potentiodynamic polarization tests of these BMGs were conducted in 3.5wt% NaCl aqueous solution. It is found that the addition of 8at% Nb into Zr41.2Ti13.8Cu12.5Ni10Be22.5 alloy results in the improvement of corrosion resistance with the pitting potential of −52 mV, the open circuit potential of −446 mV, and the corrosion current density of 9.86×10−6 mA/cm2. This may be attributed to that Nb is beneficial to passivate and stabilize Zr and Ti.

Coating thickness control in continuously fabricating metallic glass-coated composite wires

A continuous production process was developed for coating bulk metallic glasses on the metallic wire surface. The effects of processing parameters, including the drawing velocity and coating temperature, on the coating thickness were investigated. It is found that the coating thickness increases with the increase in drawing velocity but decreases with the increase in coating temperature. A fluid mechanical model was developed to quantify the coating thickness under various processing conditions. By using this theoretical model, the coating thickness was calculated, and the calculated values are in good agreement with the experimental data.

Influence of Cu content on the mechanical properties and corrosion resistance of Mg-Zn-Ca bulk metallic glasses

Abstract(Mg66.2Zn28.8Ca5)100−xCux (at%, x = 0, 1, 3, and 5) bulk metallic glasses (BMGs) of 2 mm in diameter were prepared by the conventional copper mold injection casting method. Besides, the influence of Cu content on the microstructure, thermal stability, mechanical properties, and corrosion behavior of Mg-Zn-Ca BMGs was investigated. It is found that the addition of Cu decreases the glass-forming ability of Mg-Zn-Ca BMGs. Crystalline phases are precipitated at a higher Cu content, larger than 3at%. The compressive fracture strength of Mg-Zn-Ca BMGs is enhanced by the addition of Cu. With the formation of in-situ composites, the compressive strength of the Mg-Zn-Ca alloy with 3at% Cu reaches 979 MPa, which is the highest strength among the Mg-Zn-Ca alloys. Furthermore, the addition of Cu also results in the increase of corrosion potential and the decrease of corrosion current density in Mg-Zn-Ca BMGs, thereby delaying their biodegradability.