This review attempts to present first a brief summary of the up-to-date experimental studies on amorphization transition, which results in the formation of amorphous alloys or metallic glasses, by ion irradiation of multiple metal layers in the binary metal systems Secondly, based on the framework of Miedema’s theory, thermodynamic modeling of metallic glass formation is described with consideration of the significant role of interfacial free energy of the multilayers in amorphization Thirdly, results of molecular dynamics simulations for some representative systems are presented to show the calculation of the intrinsic glass-forming ability from interatomic potential of the binary metal systems

Irradiation induced amorphization in metallic multilayers and calculation of glass-forming ability from atomistic potential in the binary metal systems

In this review article, first a brief summary is presented concerning the formation of amorphous alloys (or metallic glasses) in binary metal systems by solid-state reaction of metallic multilayers. Secondly, under the framework of Miedema's model, thermodynamic modelling of crystal-to-amorphous transition is developed with special consideration of the excess interfacial free energy in metallic multilayers. Thirdly, the results of molecular dynamics simulations in some representative systems are presented, revealing the detailed kinetics of the crystal-to-amorphous transition on the atomic scale, such as the temperature/time dependence of interfacial reactions, the asymmetric growth of amorphous interlayers, and the nucleation and/or presence of growth barriers resulting from the interfacial texture. Fourthly, the critical solid solubilities of some representative systems are directly determined from the inter-atomic potentials through molecular dynamics simulations and then correlated with the metallic-g...

Solid-state crystal-to-amorphous transition in metal-metal multilayers and its thermodynamic and atomistic modelling

Interatomic potentials of the binary transition metal systems and some applications in materials physics

A dodecagonal quasicrystalline phase was grown in nano-sized Ag-Pt multilayers upon solid-state reaction and the existence of the respective metastable state in the Ag-Pt system was also confirmed by ion-beam mixing experiments. The major driving force for intermixing between the nano-sized Ag and Pt layers, as well as for the crystal-to-quasicrystal transition, was thought to be the interfacial free energy, which elevated the initial Ag-Pt multilayers up to an energetic state corresponding to the dodecagonal phase.

Formation of a dodecagonal phase in the nano-sized Ag-Pt multilayers upon solid-state reaction

In the present review article, firstly, the experimental observations of the binary metallic glass formation by various glass-producing techniques are briefly summarized. Secondly, a detailed discussion is presented concerning the concepts of the glass-forming ability and glass-forming range (GFA/GFR) of a binary metal system. Meanwhile, some of the proposed empirical criteria or rules for predicting the binary metallic glass formation are discussed and compared with the experimental observations. Thirdly, it is proposed to take the interatomic potential of a binary metal system as the starting base to develop an atomistic theory capable of predicting the binary metallic glass formation. Accordingly, eight binary metal systems are selected as representatives to cover the various structural combinations as well as various thermodynamic characteristics. The n-body potentials of eight representative systems are then constructed with the aid of ab initio calculations. Applying the constructed and proven realistic n-body potentials, a series of molecular dynamics simulations are carried out. In the simulations, solid solution models are employed to compare the relative stability of the solid solution versus its competing disordered counterpart (i.e. the amorphous or metallic glass phase) as a function of the solute concentration. Finally, based on the realistic interatomic potentials, molecular dynamics simulations not only reveal the physical origin of the binary metallic glass formation, but also quantitatively determine, for each system, an alloy composition range, within which the disordered state is energetically favored, thus leading to establish the atomistic theory capable of predicting the GFR, i.e. the quantitative GFA, of the binary metal systems.

Atomistic theory for predicting the binary metallic glass formation

Amorphization was achieved by room temperature 200-keV xenon ion mixing in two isolated composition ranges, i.e., ${\mathrm{Y}}_{22}$--${\mathrm{Y}}_{27}$ and ${\mathrm{Y}}_{72}$--${\mathrm{Y}}_{83}$, in the Y-Mo system, which has a positive heat of mixing exceeding +26 kJ/mol. In addition, three metastable crystalline (MX) phases, i.e., a Y-rich fcc (fcc-I), a Mo-rich hcp (hcp-I), and another fcc (fcc-II) phase, were observed at different irradiation stages. Kinetically, the fcc-I MX phase was formed through a single-step transition of hcp\ensuremath{\rightarrow}fcc, while the hcp-I and fcc-II phases were formed sequentially via a two-step transition of bcc\ensuremath{\rightarrow}hcp\ensuremath{\rightarrow}fcc. To give further insight into the singularity of the amorphization behavior of the system and the MX phase formation, a Gibbs-free-energy diagram of the system was constructed by calculating the free energies of the amorphous phase, the solid solutions, three MX phases, and of the as-deposited Y-Mo multilayers, for which the interfacial free energies were added. The established diagram can explain well the irradiation-induced amorphization behavior and the MX phase formation in the Y-Mo system.

Anomalous alloying behavior induced by ion irradiation in a system with a large positive heat of mixing

This paper presents some new results obtained by the authors in some 15 binary metal systems and a brief summary concerning ion mixing (IM) synthesis of metastable alloys. (1) The metastable crystalline (MX) phases so far obtained can be classified into five types, i.e. the super-saturated solid solutions and the enlarged hcp-I phases in hcp- or fcc-based alloys reported earlier, and the newly formed fcc-I phases in hcp-based alloys, the fcc-II and hcp-II phases in bcc-based alloys. The growth kinetics of the MX phases is also discussed. (2) The interfacial free energy in the multilayered films was found to play an important role in IM induced amorphization. By adding sufficient interface, amorphous alloys can be formed by IM in a broad composition range even in a system with rather positive heat of formation ( ΔH f ), which has been predicted to hinder amorphization. (3) Gibbs free energy diagrams of some systems were constructed based on Miedema's theory. The calculation included the free energy curves of all the competing phases, especially those of the new MX phases. To check the relevance of the calculation, steady-state thermal annealing of the multilayered films was conducted and the results confirmed the calculated energetic sequence of the competing phases. The constructed diagrams can interpret the formation and evolution of the metastable phases synthesised by IM.

Metastable alloys synthesised by ion mixing and thermodynamic and kinetic modelling

Free energy diagrams for the AgMo and AgNb systems which have very large positive heats of formation at equi-atomic stoichiometry, + 56 and + 25 kJ/mol, respectively, were constructed which included consideration of the interfacial free energy present in multilayered films. The calculated diagrams suggested that amorphization was thermodynamically achievable in both systems despite their large positive heats of formation. In the case of AgMo multilayers containing 12 layers, the calculated predictions of amorphization favored Ag- and Mo-rich alloys, in agreement with experimental results of ion mixing conducted at liquid nitrogen temperature. Additionally, new metastable FCC Mo- and Nb-enriched phases were obtained at different irradiation doses. More interestingly, these FCC phases transformed into amorphous states after room temperature aging. This FCC to amorphous transition was also discussed by comparing the free energy of these states.

Unusual alloying behavior observed in the immiscible AgMo and AgNb systems under ion irradiation

A comparative study of metastable alloy formation by ion mixing and thermal annealing of multilayers in the immiscible Y–Zr system

Six binary metal systems were selected to study the possibility of forming amorphous alloys by ion mixing or thermal annealing in multilayered Films, i.e. the Ta-Cu, Zr-Nb, Zr-Ta, Y-Zr, Y-Mo and Y-Ta systems, featuring positive heats of formation (ΔH f ) ranging from +3 to +40 kJ/mol. Firstly, the interfacial free energy consisting of a chemical and an elastic terms was calculated and added to the energetic state of the multilayers. It was found that the excess interfacial free energy increased with increasing the fraction of the interfacial atoms in the multilayers, and could raise the multilayers to an energy level intersecting with or being higher than thai of the amorphous phase possessing a typical convex shape. It is therefore possible to produce amorphous alloys in such systems, if the multilayered filins included enough fraction of the interfacial atoms. The multilayered samples were then designed and prepared accordingly and both ion mixing and thermal annealing under appropriate conditions resulted in the formation of a number of new amorphous alloys, confirming the above prediction based on the interfacial free energy concern. It is noted that the success of synthesising amorphous alloys by solid-state reaction in the immiscible systems develops a new glass forming technique, namely interface-generated spontaneous amorphization, which has a great potential to produce new and relatively thick amorphous films, e.g. a Ta 72 Cu 28 amorphous film of 800 nm thick was obtained.

O. Jin

Papers

Anomalous alloying behavior induced by ion irradiation in a system with a large positive heat of mixing

Metastable alloys synthesised by ion mixing and thermodynamic and kinetic modelling

Unusual alloying behavior observed in the immiscible AgMo and AgNb systems under ion irradiation

A comparative study of metastable alloy formation by ion mixing and thermal annealing of multilayers in the immiscible Y–Zr system

Role of Interface in Ion Mixing or Thermal Annealing Induced Amorphization in Multilayers in Some Immiscible Systems