Metallic Glasses: A New Approach to the Understanding of the Defect Structure and Physical Properties

Abstract

The work is devoted to a brief overview of the Interstitialcy Theory (IT) as applied to different relaxation phenomena occurring in metallic glasses upon structural relaxation and crystallization. The basic hypotheses of the IT and their experimental verification are shortly considered. The main focus is given on the interpretation of recent experiments on the heat effects, volume changes and their link with the shear modulus relaxation. The issues related to the development of the IT and its relationship with other models on defects in metallic glasses are discussed.

Heat Effects Occurring in the Supercooled Liquid State and Upon Crystallization of Metallic Glasses as a Result of Thermally Activated Evolution of Their Defect Systems

“…It is seen that G(T)-patterns for all MGs are quite similar. Heating of glassy samples leads to a monotonous decrease of G while the slope |dG/dT| decreases by several times near T g , which constitutes a typical behavior upon high-frequency G-measurements [17]. Heating by 50-70 K above T g results in the beginning of crystallization, which leads to an increase of the shear modulus by 22% (ZrFe 1 ) to 40% (ZrNi 10 ).…”

“…Heat effects can be then interpreted in terms of the changes of the defect concentration. This approach provides quantitative explanations for quite a few other relaxation phenomena in MGs [17].…”

“…A description of the heat effects within the framework of the IT is based on an expression for the formation enthalpy of interstitial-type defects [11,12], H = αΩG, where the dimensionless α ≈ 1 is related to the defect strain field [18], Ω is the volume per atom and G is the unrelaxed shear modulus. The latter is related to the defect concentration c as G = µ exp(−αβc), where µ is the shear modulus of the maternal crystal (i.e., the one, which was melted and then used for glass production by melt quenching) measured at the same temperature and the dimensionless shear susceptibility β characterises the anharmonicity of the interatomic potential and by the definition equals the ratio of the fourth-order non-linear shear modulus to the second-order (i.e., "usual") shear modulus [17]. Typically, β = 15 − 20 depending on MGs' chemical composition [17].…”

“…The latter is related to the defect concentration c as G = µ exp(−αβc), where µ is the shear modulus of the maternal crystal (i.e., the one, which was melted and then used for glass production by melt quenching) measured at the same temperature and the dimensionless shear susceptibility β characterises the anharmonicity of the interatomic potential and by the definition equals the ratio of the fourth-order non-linear shear modulus to the second-order (i.e., "usual") shear modulus [17]. Typically, β = 15 − 20 depending on MGs' chemical composition [17].…”

Recent Advancements in Metallic Glasses

“…Khonik and Kobelev [8] present a brief overview of the Interstitialcy theory as applied to different relaxation phenomena occurring in metallic glasses upon structural relaxation and crystallization. The basic hypotheses of this theory and their experimental verification are briefly considered.…”