Influences Of Intrinsic Factors On Vitrification And De-vitrification Of Alloy Systems

Metallic glasses have attracted increasing interests for their unique physical, chemical, mechanical and good anticorrosion properties since the first report of successful preparation by Duwez from Caltech in 1960s. Especially in the late of 1980s, the breakthrough of limitation in size of traditional metallic glass by the development of bulk metallic glasses makes them valuable and promising in their application. Nevertheless, the basic question still remains unresolved: what kind of alloy systems can be formed into metallic glass and what kind of metallic glasses are likely to be the stablest. There are also no unique theory or universal parameters to indicate glass forming ability though many theories including confuse principle, eutectic principle, atomic size criterion and glass-forming enthalpy criterion tried to solve it. In this dissertation, a parameter which related to glass-forming enthalpy, solid solution forming enthalpy, intermetallic forming enthalpy and some atomic factors calculated by Miedema's model is proposed to indicate the glass-forming ability. The intrinsic factors like effective electronegativity difference and effective atomic size difference among multi-component alloy systems are suggested to evaluate vitrification ability and the tendency of devitrification. The main contents and conclusions are as follows.1 On the viewpoints that the difference between intermetallics and solid solutions mainly lies to the ordering degree of chemical structure and the difference between intermetallics and metallic glasses mainly lies to the ordering degree of topological structure, a ratio of chemical ordering enthalpy to topological ordering enthalpy (φ) is proposed to indicate glass forming ability for binary and multi-component alloy systems. Zr-, La- and Sm-based multi-component bulk metallic glasses are made by vacuum suction-casting and water quenching in order to investigate the relationship between the ratio and glass forming ability. Moreover, the effects of beryllium with little atomic size and cerium with low melting point on glass forming ability are analyzed by the ratio.2 According to the condition of glass-formingφ>1, the glass forming ranges are obtained from x=0.05 to x=0.88 for Zr_xCu_1-x binary and x=0.26 to x=0.89 for NixNb1-x binary alloys. The ranges for bulk metallic glasses determined by experiments are 0.35 to 0.55, which the value ofφis greater than 3.1, and for Ni-Nb binary alloys, the experimental results show that the best glass formers are in the ranges of x=0.615 to x=0.625, thus the value determined is over 1.84.3 When the ratioφis greater than 1.2, Zr-Cu-Al ternary alloys can be formed into bulk metallic glasses. It needs to reach 1.464 for Zr-based quinary alloys, 3.0 for La-based alloys and 2.387 for Sm-based quarternary and quinary alloys.4 The substitution of Be with small atomic size for Zr element in Zr_0.65-xAl_0.1Ni_0.1Cu_0.15Be_x(x=0～0.15)quinary alloys makes an increase of chemical ordering enthalpy and a decrease of topological ordering enthalpy, which increases glass forming ability. The substitution of cerium for Sm in Sm_55-xCe_xAl₂₀Ni₁₀Cu₁₅ depressed both chemical ordering enthalpy and...