| Since the discovery of Au-Si glass in 1960, many efforts have been made to understand the mechanisms for high glass-forming ability (GFA) of metallic glasses (MGs) and to hunt new bulk MGs for industrial applications. A number of criteria and parameters have been proposed to measure the GFA of MGs, for instances, the atomic-packing efficiency, Inoue’s empirical rules, the width of supercooled liquid region(△Tx), the reduced glass transition temperature (Trg), and y factor, etc. Up to date few studies have been reported in concerning the relationship between the properties of liquid melts and the GFA of MGs, most likely due to the difficulties in preventing liquid melts from oxidation at high temperatures. Thus, in this thesis, we attempt to study the thermal behaviors of two MG systems:one is La-based including La62Al14Cu24(S-1) and La62Al14(Cu5/6Ag1/6)14Ni5Co5(S-2) with critical sizes of 4 mm and 20 mm diameter, and another is Zr-based (Zr46Cu46Al8, Zr46Cu5/6Ag1/6)46 Al8 and Zr46Cu30.14Ag8.36Al8Be7.5 with critical size of 8mm,>20mm and 73mm) and the correlations with their different GFA measured by a dilatometer with a self-sealed sample cell. Also, the thermal behavior of liquid Ga7oBi3o alloy is measured. The mainly achieved results are listed as follows:1) From 850K to 1273K, the length change rate of liquid S-1 and S-2 with temperature can be expressed as:ALs-1=-3.90 x 10-3-7.66 x 10-6T+2.42 x 10-8T2, △Ls-2=-9.80 x 10-3-7.14 x 10-6T+2.66 x 10-8T2, respectively. The thermal expansion coefficients of both melts are αs-1= 4.84 × 10-8T - 7.66 × 10-6 and as-2= 5.32 × 10-8T-7.14 × 10-6. Accordingly, the liquid density of them can be described as:PS-1= 6.10-7.43 × 10-5T-1.38 × 10-7T2 and Ps-2= 6.09-1.62 × 10-5T-1.49 × 10-7T2. It is found that the thermal expansion coefficient of the liquid S-1 is larger while the density is smaller than that of the liquid S-2. Therefore, the high GFA of S-2 alloy can be mainly ascribed to the denser atomic packing and the slower atomic rearrangements in liquid melts.2) We obtained the thermal expansion coefficients of Z46C46Al8, Zr46(Cu5/6Ag1/6)46Al8 and ZrCu30.14Ag8.36Al8Be7.5 in the amorphous state are of about (1.33 ± 0.005) ×10-5 K-1, (1.145 ± 0.003) × 10-5 K-1, (1.164 ± 0.005) × 10-5 K-1, respectively; and in the crystalline state are of (0.964 ± 0.005) x 10-5 F-1,(1.021 ± 0.002) × 10-5 K-1,(1.102 ± 0.003) × 10-5 K-1, respectively. We also found that this method is unsuitable to measure the liquid melts of Zr-based MGs, most likely the high wetability with the sample cell leading to the seepage during the measurements.3) The thermal behavior of liquid Ga70Bi30 is measured by the same method from 500K to 1300K. The result shows that the length change is not exactly linear from 500K to 560K, mainly caused by the coexistence of two different liquid phases in this temperature range. The thermal expansion coefficient of Ga7oBi3o is (1.00±0.2) x 10-5 K-1 from 600K to 1070K, and increases to (1.20 ± 0.2) x 10-5 K-1 from 1170K to 1300K, suggesting that a liquid-liquid phase transition may exist at 1080K. |
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