Papers by Author: Wei Zhang

Abstract: In this paper, the effects of the processing parameters on the preparation of Nb₄₂Ni₄₀Co₁₈ amorphous alloy ribbons were analyzed in detail, including the property of the alloy, material and size of the injection nozzle, setting of the alloy ingots, the distance between the nozzle and the copper wheel, surface quality and velocity of the copper wheel, heating rate and time, injection pressure, injection time, etc. Finally key factors for preparing wide Nb₄₂Ni₄₀Co₁₈ amorphous alloy ribbon have been proposed.

Abstract: With the aid of the atomic-cluster-plus-glue-atom model (ACPGA model) proposed by Dong et al [1] for bulk metallic glasses (BMGs), the formation and characteristic of Ni-Ta binary BMGs were investigated in this work. Binary glass-forming compositions containing 56.3–62.5 at.%-Ni were obtained by a composition formula [M-Ni₆Ta₆]Ni₃ based on the ACPGA model. It was found that Ni-Ta BMGs with a diameter of 2 mm was obtained over a composition range of 59 ~ 62 at.%-Ni by copper mold casting method, which are in good agreement with our model prediction. Newly-developed Ni–Ta BMGs are a kind of extreme materials, which exhibit superior thermal stability (T_g = 993K) and a ultrahigh fracture strength of about 3.5 GPa.

Abstract: A new series of bulk metallic glasses were developed by addition of Fe into the ternary Zr60Cu30Al10 alloy. Although Fe-Cu element pair shows distinct immiscibility with a large positive heat of mixing, substitution of Fe for Cu significantly improves the glass-forming ability of the ternary Zr60Cu30Al10 alloy. The critical diameter for glass-formation increases from 8 mm for Zr60Cu30Al10 alloy to 20 mm for Zr60Cu25Fe5Al10 and Zr62.5Cu22.5Fe5Al10 alloys. As compared with the ternary Zr60Cu30Al10 alloy, the new quaternary Zr-Cu-Fe-Al alloys show lower liquidus temperatures. The Zr60Cu25Fe5Al10 and Zr62.5Cu22.5Fe5Al10 alloys, the best BMG-formers in this alloy system, are found to locate very near a Zr-Cu-Fe-Al eutectic point. The new Zr-Fe-Cu-Al bulk metallic glasses exhibit high strength of about 1700 MPa. The plastic strain increases from 7.8% to 11.3% with increasing the content of Fe from 0 to 12.5%. The finding of a Ni-free Zr-based bulk glassy alloy with the extremely high glass-forming ability is expected to extend the future application of bulk metallic glasses.

Abstract: The thermal stability and crystalline phases precipitated from the as-cast rods of the Cu50Zr50-based alloys with addition of Al or simultaneous addition of Al/Ti or Al/Ag elements were investigated using DSC, DTA and XRD. The value of
Tx, Trg and γ as a function of alloy composition shows a same trend, in which the Cu46Zr46Al8 alloy exhibits the largest value of
Tx, Trg and γ. However, this trend is different from the variation of the dc with alloy composition, in which the Cu42Zr42Al8Ag8 alloy has the largest dc for glass formation. Trg′ based on Tg/Tm has a good correlation with the critical diameter for glass formation in this alloy system. It was found that the alloy with higher GFA has more complex precipitated crystalline phases from the as-cast rod with a diameter larger than the critical diameter for glass formation.

Abstract: Phase transformation in the melt-spun (Zr65Al7.5Cu27.5)95Ti5 glassy alloy was investigated by a combined use of X-ray diffraction (XRD), transmission electron microscopy (TEM) and differential scanning calorimetry (DSC). It was found that the crystallization mode of the Zr65Al7.5Cu27.5 glassy alloy was altered by the addition of Ti, and nanometer scaled icosahedral phase (I-phase) formation was observed in the primary crystallization stage of the (Zr65Al7.5Cu27.5)95Ti5 quaternary glass, which transformed to the stable Zr2Cu-type phase upon further annealing. The crystallization behavior of (Zr65Al7.5Cu27.5)95Ti5 glass was further discussed in terms of the activation energy as compared to that of Zr65Al7.5Cu27.5 alloy.

Abstract: The addition of Ti and Zr to Ni-Ta binary alloys is effective for the increase in stabilization of supercooled liquid and glass-forming ability (GFA). As the Ti content increases, the supercooled liquid region
Tx and reduced glass transition temperature (Tg/Tl) of Ni60Ta40-xTix glassy alloys increase, show maximum values of 63 K at 20 at.%Ti and 0.589 at 25 at.%Ti, respectively, and then gradually decrease. The addition of 5 at.% Zr to Ni-Ta-Ti alloys lowers liquidus temperature (Tl), resulting in the higher Tg/Tl values of 0.600. The best GFA were obtained for Ni60Ta15Ti20Zr5 and Ni60Ta20Ti15Zr5 alloys and the glassy alloy samples with a diameter of 1.0 mm were fabricated. The new Ni-Ta-based bulk glassy alloys exhibit high Tg of ~897 K, large ΔTx of ~74 K, high strength of over 3180 MPa with plastic strains of ~0.4% and excellent corrosion resistance in 1 N HCl solution.

Abstract: Using ultrasonics, acoustic characteristics of Pd40Cu30P20, Zr55Cu30Al10Ni5, Zr65Pd12.5Ni10Al7.5 Cu5, Cu55Zr30Ti10Pd5, Cu45Zr20Hf25Ag10 and Ti41.5Cu42.5Ni7.5Hf5Zr2.5Sn1 glassy alloys were examined in terms of complex elasticity. The order of bulk modulus (K), Lamè parameter (λ ), Young (E ) and shear (G ) moduli of the glassy alloys is monopoltical character of glassy alloys, except for polymers and rubbers. For metals and alloys, ceramics, polymers and glassy alloys, Poison’s ratio correlates well to ratio G /K. Complex elasticity indicates that viscoelasticity of the glassy alloys is predominated by volumetric motion.

Abstract: The present paper investigates the bulk metallic glass formation in Co-based alloy systems with the guidance of the cluster line and minor-alloying principles. The selected basic ternary Co-B-Si alloy compositions are intersecting points of cluster lines, defined by linking special binary clusters to the third element. Then these basic ternary alloys are further minor-alloyed with Nb and quaternary bulk metallic glasses are obtained only by 4-5 at. % Nb minor-alloying of the basic composition Co68.6B25.7Si5.7 that is developed from dense-packed cluster Co8B3. The bulk metallic glasses are expressed approximately with a unified simple composition formula: (Co8B3)1(Si,Nb)1. In addition, a quantity of Fe substitution for Co further improves the glass-forming abilities.

Abstract: We investigated the crystallization behavior of the melt-spun Cu50Zr45Ti5 alloy ribbon on thermal annealing and electron irradiation using a transmission electron microscopy (TEM). The structure composed of a monoclinic CuZr phase with an average grain size of about 8 nm and a glassy matrix was formed by electron irradiation induced crystallization, while by thermal annealing the equilibrium Cu10Zr7 and CuZr2 crystalline phases directly precipitated in the glassy phase of the Cu50Zr45Ti5 glassy alloy.

Abstract: XAFS measurements of the Cu, Ni and Zr K-edges for the melt-quenched Zr67Cu33 and Zr67Ni33 metallic glasses were curried out using synchrotron radiation at 20K. Fitting calculations for the EXAFS results reveal that local structure around Ni and Zr in Zr67Ni33 is well represented by those for the crystalline Zr2Ni, while local structure around Zr in Zr67Cu33 is better fitted by an icosahedron rather than crystalline Zr2Cu. Such differences of the local structure attribute to the differences of the stability of super-cooled liquid state and glass formability between Zr67Cu33 and Zr67Ni33 metallic glasses.