Computer-Aided Development of Multicomponent Metallic Glasses

Abstract

A synthesized calculation model for developing metallic glasses has been created by taking into account criteria for the achievement of high glass-forming ability (GFA) and viscosity. The model deals with amorphous-forming composition region (AFCR), crystallization temperature (T x ) and three GFA factors: critical cooling rate (R c ), reduced glass-transition temperature (T g /T m ) and supercooled liquid region (∆T x =T x -T g ) where T g and T m are glass transition and melting temperature, respectively. The principle of the model is based on thermodynamic functions for multicomponent systems, i.e., mismatch entropy and mixing enthalpy which express the criteria in terms of the number of elements, atomic size differences and the heat of mixing. By combining these thermodynamic quantities with the Miedema's semi-empirical model, AFCR was calculated, and was compared with the experimental results. The GFA factors were also analyzed from viscosity. The R c was derived from transformation diagram of metallic glasses for crystallization while ∆T x was calculated by solving a differential equation expressing the change in free volume with temperature. As a result of these analyses, R c -T g /T m and R-∆T x diagrams were found to fit with the experimental results qualitatively. Furthermore, crystallization temperature (T x ) was also calculated for multicomponent metallic glasses by the modification of the Miedema's binary model for the calculation of T x . The reduced crystallization temperature (T x /T l ), where T l is liquidus temperature, was calculated for evaluating GFA of metallic glasses instead of T g /T m . Some of the calculation methods used in the present study have the advantage giving results as a function of composition; thus, there exists possibility to lead to the prediction of glassy alloys compositions. In this sense, the present calculation methods are completely different to the current method for the development of new metallic glasses relying on the empirical criteria which suggest only appropriate systems and/or elements of the alloys for the achievement of high GFA. In near future, this kind of calculation technique can be used for the prediction of optimal compositions of the metallic glasses with high GFA.

Phase Stability of an Amorphous Phase Against Electron Irradiation Induced Crystallization in Fe-Based Metallic Glasses

“…Takeuchi suggested chemical mixing enthalpy (ÁH chem ) and mismatch entropy normalized by Boltzmann constant (S =k b ) for predicting GFA. [52][53][54] The TD 298 shows the clear positive correlation with ÁH chem nomarized by the largest negative value ðÁH chem Þ L.N. and (S =k b ) normalized by the maximum value ðS =k b Þ max in Fe-Zr-B alloys and Fe-Nd-B alloys.…”