Papers by Keyword: Glass Forming Ability (GFA)

Abstract: The dynamic viscosities of molten Zr₅₅Ni₅Al₁₀Cu₃₀ and Zr₅₀Cu₅₀ alloys were measured by using rotating cylinder method under non-vacuum condition. According to the lnη~1/T curves, discontinuous changes were found and the activation energy was calculated. The activation energy of molten Zr₅₅Ni₅Al₁₀Cu₃₀ alloy is obviously larger than that of molten Zr₅₀Cu₅₀ alloy. Amorphous sample of Zr₅₅Ni₅Al₁₀Cu₃₀ with 3mm diameter was prepared successfully under non-vacuum condition, but there are crystallization phases in Zr₅₀Cu₅₀ amorphous sample with 2mm diameter. The relationship between viscosities of molten Zr-Cu based alloys and their glass forming ability (GFA) was discussed, and viscosities of molten Zr-Cu based alloys play an important role on their GFA.

Abstract: The glass forming ability, thermal stability and non-isothermal crystallization kinetics of Zr64Al10.1Cu11.7Ni14.2 glass forming alloy were investigated. Its maximum glass forming dimension is up to 5mm and its critical cooling rate is less than 40Ks-1. The apparent activation energies derived from the Kissinger for Eg, Ex, Ep1 and Ep2 are 244.97±12.90, 264.63±10.18, 268.75±40.10 and 222.34±24.12 KJmol-1, respectively. The fragility parameter m is about 20.27, indicating its better thermal stability and glass forming ability.

Abstract: The RE4Fe72B22M2 (RE=Y, Dy or Nd; M=Nb or Ta) alloys in ribbon and rod forms were prepared by melt spinning and water cooling copper mold casting methods, respectively. Amorphous structure was observed in all ribbon samples, but the results from rod samples indicated that the composition has an important effect on the glass formability. All rod samples with RE=Y or Nd were partly amorphous, while bulk metallic glass (BMG) rod with a diameter of 2 mm was obtained for the Dy4Fe72B22Nb2 alloy. The rare earth and doping elements on the glass formability have been discussed. The effects of post-annealing on the microstructure and magnetic properties of these alloys have been investigated. The results presented here provide a viable method to get fully dense bulk hard magnets.

Abstract: In the past research on bulk metallic glasses (BMGs) has been concentrated on searching for alloy composition to obtain high glass forming ability. Very few studies are on the effect of processing condition on glass forming ability of BMGs. In this study, we have prepared CuZr-based BMGs at different casting temperatures. Increasing casting temperature increases glass forming ability and decreases the amount of the crystalline phase during BMG solidification. At a high casting temperature 1723 K, fully amorphous sample is obtained at a size of 2 mm in diameter. While under the lower casting temperatures (1523 K and 1323 K), crystalline CuZr phases exist. The formation of the crystalline phase is attributed to the initial crystals or cluster survived in the BMG melt during ingot remelting. The study indicates that casting temperature can be used as the controlling parameter to produce purely amorphous materials or crystalline CuZr-phase reinforced BMG composites, and the mechanical properties and thermal stability of the BMG composites can be tailored by the amount of the crystalline phase existed in the materials.

Abstract: Flakes with a size of 20×4×0.8mm3 and rods of (Fe68B25Nd7)96Nb4 bulk metallic glass (BMG) with a diameter of 1.5 and 3mm were cast. Rods a diameter of 1.5 mm were proven to be XRD amorphous. High vacuum environment during the fabrication will benefit the formation of fully amorphous BMG. The super-cooled liquid regions of (Fe68B25Nd7)96Nb4 is 59°C and the reduced glass transition temperature is 0.624 indicating good glass-forming ability. The critical cooling rate for glass formation for (Fe68B25Nd7)96Nb4 melt is about 294°C/s by computer simulation (Fe68B25Nd7)96Nb4 BMG shows soft magnetic property while partially crystallized sample shows hard magnetic property.

Abstract: Special remelting techincs including repeating the heating and quenching process for several times, electromagnetic mixing during the melting, increasing the superheating temperature, prolonging isothermal time can effectively decrease or remove the effect of impurity in raw materials on the glass-forming ability (GFA) of the alloy system. These technics were introduced to improve GFA of Fe60Co8Zr10Mo5W2B15 alloys (△Tx = 64 K, Trg = 0.61, Trg’= 0.59). Bulk metallic glasses of Fe60Co8Zr10Mo5W2B15 with the shape of rods (φ3×40) and plates (1×10×20) were casted into fully glassy state. It was proved the GFA of Fe60Co8Zr10Mo5W2B15 with industrial raw materials is very close to that with high purity raw materials. Fe60Co8Zr10Mo5W2B15 bulk metallic glass with industrial raw materials shows better potential appliance for their low cost.

Abstract: The relationship between the viscosity of Al84Mg10Ce6 alloy melt and liquid structure was studied by viscosity measurements, X-ray diffraction and DSC analysis in this paper. In addition, the glass forming ability of alloy ties produced by melt spinning was analyzed. Based on the above results, the relationship between alloy melts and its glass forming ability(GFA)was studied. The addition of element Ce leads to the abnormal change of Al84Mg10Ce6 melt’ s structure and enhances its GFA, furthermore, it results in completely amorphous ties with melt spinning at 850°C.Therefore, there is certain relationship between the Al-Mg based alloys melt and its GFA.

Abstract: The aim of this research is to clarify a quantitative evaluation in the structural relaxation processes focusing on the activation energy in Cu based amorphous alloys. The activation energy for structural relaxation process in a metal type amorphous CuHfTi ternary alloys, with cross sections of typically 0.03 mm x 2.0 mm, prepared by chill-block melt spinning has been investigated by Differential Scanning Calorimetry (DSC) with a cyclically heating technique. Activation energies for structural relaxation with a spatial quantity in amorphous materials have been discussed by use of a relaxed ratio function that depends on annealing temperature and time. In the present work, the distributions for the Activation Energy Spectrum (AES) were observed almost 152 kJmol-1 (1.58 eV). Another result has been also established that the “reversible” AES model energy distribution though the cyclically structure relaxation occurs even in amorphous Cu60Hf20Ti20 alloy.

Abstract: The paper makes a review about the opportunity, forming conditions and obtaining methods of bulk amorphous alloys and their properties. There are also presented the experiments regarding the obtaining and characterization from mechanical and chemical point of view of some alloys from Fe70 (Cr5-x Nix)5 Ga4 P13 Si5 C3 ( x = 0,1,2,4) family, pointing out the negative effect of the nickel on their resistance characteristics.

Abstract: Mg bulk metallic glass rod, ribbon and composite plate were synthesized via injection casting, melt spinning, and spray forming, respectively. The BMG composite plate has various microstructure combinations, from fully amorphous phase to mixture of nanocrystals, crystals and amorphous phase. XRD analyses were done on the rod and ribbon and throughout the vertical locations of the plates at the maximum thickness. Glass transition temperature (Tg) and onset crystallization temperature (Tx) were measured with DSC, and GFA (Glass Forming Ability) was estimated with various GFA models. The microhardness of the spray-formed Mg-Cu-Gd layered composite plate at various positions and Mg-Cu-Gd rod and ribbon were measured.