Papers by Keyword: Glass Forming Ability (GFA)

Abstract: The aim of the paper was investigation of the effect of Cu addition on glass forming ability (GFA), thermal stability, structure and magnetic properties of Fe-Co-based bulk metallic glasses (BMGs). The raw materials used in this experiment for the production of BMGs were pure Fe, Co, Cu and industrial Fe-B, Fe-Si, Fe-Nb ferroalloy. Investigations were carried out on BMGs in rods shaped with square section with side of 1.5mm. The structure of the investigated BMGs in rod form is amorphous. The addition of small amounts of Cu is effective in changing GFA and magnetic properties. The melting temperature - Tm remained almost constant for both investigated alloy. Two alloy compositions are at or very close to the eutectics, what according to ref. [1] should guarantee the best metallic glass-forming alloys. The investigated alloys have good soft magnetic properties. The successful synthesis of the Fe36.00Co36.00B19.00Si5Nb4 and Fe35.75Co35.75B18.90Si5Nb4Cu0.6 alloys with high GFA and good soft magnetic properties by using starting industrial alloys are encouraging for the future industry applications.

Abstract: The effect of the addition of 0.2-0.65 at% of V on the glass forming ability and mechanical properties of Al88Y7Fe5 alloy were investigated. The addition of V in this range had little effect on the glass forming ability of the alloy, but lowered the tensile strength of the amorphous ribbon. The fracture surface of Al88Y7Fe5 amorphous ribbons was typical vein pattern for ductile metallic glasses, however, that of the alloy with 0.5% V addition changed to two different regions, i.e., vein pattern region and smooth region. At high magnification, the smooth region was composed of nanometer sized corrugations, which is typical for brittle metallic glasses.

Abstract: Evaluation of glass-forming ability (GFA) is important in the development of amorphous alloys. Based on phase field theory, the kinetic model of liquid-to-solid phase transition is build, and the time-temperature-transformation (TTT) diagram is plotted according to the phase field simulations of isothermal phase transformation kinetics for a model system. Furthermore, the critical cooling rate for glass formation is calculated on the basis of the TTT curve and is taken as the intrinsic criteria of reflecting the GFA for metallic melts.

Abstract: Bulk metallic glasses (BMGs) of Cu45Zr48-xAl7Tix with x= 0, 1.5, and 3 at.% were prepared by copper mould casting. The corrosion resistance of the BMGs with different Ti contents was examined by potentiodynamic polarization tests and weight loss measurements in 1 N NaOH, 1 N H2SO4, 1 N H2SO4 + 0.01 N NaCl and 0.5 N NaCl solutions, respectively. The newly-developed BMGs’ corrosion resistance in Cl-- or both H+ and Cl--ions containing solutions can be greatly enhanced. The influence of Ti addition on glass forming ability (GFA) and thermal stability was investigated by x-ray diffraction and differential scanning calorimetry in detail. The alloy containing 1.5 at.% Ti exhibits the largest GFA, the critical size comes up to 10 mm in diameter.

Abstract: Multi-component Hf_45.6Cu_27.8Ni_9.3Ti₅Al_12.4 bulk metallic glasses (BMGs) were prepared successfully by casted into the water-cooled Cu mold. Characterization of the casted Hf_45.6Cu_27.8Ni_9.3Ti₅Al_12.4 rods was carried out by X-ray diffraction. The thermal stability and crystallization kinetics were followed by differential scanning calorimetry. The results show that the alloy Hf_45.6Cu_27.8Ni_9.3Ti₅Al_12.4 had a critical cylindrical rod diameter for glass formation, Dc, of 7 mm and the largest cross-sectional diameter (about 12.4mm) can be obtained in the ideal condition. The critical cooling rate for glass formation is 6.48K/s. The Hf_45.6Cu_27.8Ni_9.3Ti₅Al_12.4 BMG has larger glass forming ability and higher thermal stability.

Abstract: The mechanism of melt treatment improving the glass forming ability (GFA) and thermal stability of the Al_84.5Ni_5.5Y₁₀ (in atomic percentage) alloy was studied. An yttrium-rich metastable high-melting-temperature-phase is found to be responsible for the deterioration of GFA because it induces the heterogeneous nucleation of the crystals in the solidification process. It can be eliminated through melt treatment as adopted in this paper, resulting in stabilizing the thermal stability of the undercooled melt and enhancing the GFA of the investigated alloy with higher thermal stability for the resultant amorphous phase.

Abstract: In the present study, the Zr-Cu-Ni-Al based bulk metallic glasses with different Ti addition was successfully prepared by suction casting . It was found that the glass forming ability was improved with increasing of Ti content from 3 at.% to 7 at.%. However, with increasing of Ti content, the room-temperature plasticity decreased from 4.33% to 0.66 %.

Abstract: The glassy alloy rods of Cu₅₀Zr₄₃Al₇, (Cu₅₀Zr₄₃Al₇)_100-xY_x(x=2,5) and (Cu₅₀Zr₄₃Al₇)_100-xAg_x(x=6,7) with diameters of 3.0 mm were prepared by copper mold suction casting method. The influence of adding Ag and Y to Cu₅₀Zr₄₃Al₇ metallic glass on glass formation ability (GFA) and thermal stability was studied by means of X-ray diffraction analysis (XRD) and differential scanning calorimetry (DSC). The results show that Ag and Y appropriate micro-addition enhance the glass formation ability and thermal stability of the Cu-Zr-Al metallic glass. The effect of Ag is better than that of Y. The addition of Ag causes a increase of the reduced glass transition temperature (T_rg) of (Cu₅₀Zr₄₃Al₇)_100-xAg_x alloy from 0.618 at 0 at.% Ag to 0.628 at 7 at.% Ag. The width of the supercooled liquid region of Cu₄₃Zr₄₃Al₇Ag₇ glassy alloy increases about 25K compared with that of Cu₅₀Zr₄₃Al₇, and the γ value of Cu₄₃Zr₄₃Al₇Ag₇ reaches 0.433. The electrochemical corrosion behaviors of Cu₅₀Zr₄₃Al₇, (Cu₅₀Zr₄₃Al₇)_100-xY_x(x=2,5) and (Cu₅₀Zr₄₃Al₇)_100-xAg_x(x=6,7) metallic glasses in 3.5% NaCl solution were investigated by potentiodynamic polarization method. It is found that corrosion resistance of all amorphous alloys is better than that of the corresponding crystalline alloys. The Ag and Y micro-addition improve corrosion resistance of Cu₅₀Zr₄₃Al₇ metallic glass. The corrosion current density of Cu₄₃Zr₄₃Al₇Ag₇ metallic glass decreases 1~2 orders of magnitude compared with that of Cu₅₀Zr₄₃Al₇.

Abstract: Knowledge of glass forming ability (GFA) of amorphous metallic alloys is very important from both theoretical and practical point of view. Thermodynamically, the Gibbs free energy difference, ΔG between the undercooled liquid and the corresponding crystalline state is driving force for crystallization. As a consequence, it is a good indicator for glass forming ability of metallic glasses. A novel expression for ΔG has been used to estimate the GFA of recently developed Ca-based bulk metallic glasses viz. Ca53Mg23Cu24,Ca65Mg15Cu20,Ca40Mg25Cu35, Ca50Mg22.5Cu27.5 and Ca55Mg15Cu30. Different GFA criteria are also evaluated for systems taken up in the study and effect of addition of variation in composition of Ca-Mg-Cu system is also investigated. Present work suggests that among different GFA criteria, ΔG is the best criterion for the prediction of GFA for Ca-based bulk metallic glasses.

Abstract: Along nucleation → crystalline growth →crystalline fraction → critical cooling rate, the relationship between the nucleation, elements, cooling rate and the Glass Forming Ability of (Cu-Zr) based glass alloys is quantitatively studied with thermodynamics method, and a better method to evaluate the critical cooling rate of glass alloys is also proposed in this paper. The computed results show that: (1) with the increase of element number, the steady state nucleation rate drops gradually. From Cu-Zr, Cu-Zr-Al, Cu-Zr-Al-Ni, to Cu-Zr-Al-Ni-Ti, the peak value of nucleation rate decreases from 10²¹ mol^-1s^-1 to 10¹³ mol^-1s^-1. It is also found the nucleation rate both drops with the substitution of Ni with Cu or Al with Zr; (2) with the increase of cooling rate, the nucleation rate drops sharply. When the cooling rate reaches 10³K/s, the nucleation rates of Cu₆₄Zr₃₆, Cu₅₄Zr_42.5Al_3.5, Cu₅₅Zr₄₀Al₅ and Cu₃₀Zr₅₅Al₁₀Ni₅ drop to 10⁹mol^-1s^-1, 10⁶mol^-1s^-1, 10⁷mol^-1s^-1 and 10³mol^-1s^-1 accordingly.