For the family of Cu–Ni–Ti (Zr, Hf) systems, which are promising for obtaining bulk metallic glasses, glass formation regions were calculated based on the extended Miedema’s model and Alonso’s method. It is found that the calculated glass formation regions of the Cu–Ni–Zr and Cu–Ni–Hf systems agree well with experimental results, whereas it does not for the Cu–Ni–Ti system. The composition dependence of the glass forming ability in the Cu–Ni–Ti (Zr, Hf) systems were then predicted, and it turns out that the glass forming ability of the Cu–Ni–Ti system largely deviates from the experimental results, from which it is assumed that kinetic factors (low liquidus temperature) instead of thermodynamic factors cause the Cu-rich composition to easily form glass in the Cu–Ni–Ti system. Meanwhile, the effect of Ti (Zr, Hf) on the glass forming ability was discussed in terms of the mixing enthalpy and atomic size effect.

An interatomic potential was constructed for the Ni–Zr–Mo ternary metal system with the newly proposed long-range empirical formulism, which has been verified to be applicable for fcc, hcp and bcc transition metals and their alloys. Applying the constructed potential, molecular dynamics simulations predict a hexagonal composition region within which metallic glass formation is energetically favored. Based on the simulation results, the driving force for amorphous phase formation is derived, and thus an optimized composition is pinpointed to Ni45Zr40Mo15, of which the metallic glass could be most stable or easiest to obtain. Further structural analysis indicates that the dominant interconnected clusters for Ni64Zr36−xMox MGs are 〈0, 0, 12, 0〉, 〈0, 1, 10, 2〉, 〈0, 2, 8, 2〉 and 〈0, 3, 6, 4〉. In addition, it is found that the appropriate addition of Mo content could not only make a more ordered structure with a higher atomic packing density and a lower energy state, but also improve the glass formation ability of Ni–Zr–Mo alloys. Moreover, inherent hierarchical atomic configurations for ternary Ni–Zr–Mo metallic glasses are clarified via the short-range, medium-range and further in the extended scale of the icosahedral network.

With the aid of ab initio calculations, a realistic interatomic potential was constructed for the Mg–Cu–Y ternary system under the proposed formalism of smoothed and long-range second-moment approximation of tight-binding. Taking the potential as the starting base, an atomistic computation/simulation route was developed for designing favored and optimized compositions for Mg–Cu–Y metallic glass formation. Simulations revealed that the physical origin of metallic glass formation is the collapse of crystalline lattice when solute concentration exceeds a critical value, thus leading to predict a hexagonal region in the Mg–Cu–Y composition triangle, within which metallic glass formation is energetically favored. It is proposed that the hexagonal region can be defined as the intrinsic glass formation region, or quantitative glass formation ability of the system. Inside the hexagonal region, the driving force for formation of each specific glassy alloy was further calculated and correlated with its forming ability in practice. Calculations pinpointed the optimized stoichiometry in the Mg–Cu–Y system to be Mg64Cu16Y20, at which the formation driving force reaches its maximum, suggesting that metallic glasses designed to have compositions around Mg64Cu16Y20 are most stable or easiest to obtain. The predictions derived directly from the atomistic simulations are supported by experimental observations reported so far in the literature. Furthermore, Honeycutt–Anderson analysis indicated that pentagonal bipyramids (although not aggregating to form icosahedra) dominate in the local structure of the Mg–Cu–Y metallic glasses. A microscopic picture of the medium-range packing can then be described as an extended network of the pentagonal bipyramids, entangled with the fourfold and sixfold disclination lines, jointly fulfilling the space of the metallic glasses.

For the Mg–Ni–Y system, a typical Mg-based bulk metallic glass forming system, glass formation compositions are first predicted by thermodynamic calculations based on the extended Miedema’s model, suggesting that metallic glasses in the system are favored over a large composition range. Assisted by ab initio calculations, a realistic Mg–Ni–Y n-body potential is then constructed under a proposed modified tight-binding scheme. Based on the potential, an atomistic modeling scheme is further formulated for designing the favored, and even pinpointing the optimized, compositions at the atomic level. A hexagonal glass formation region is located for the Mg–Ni–Y system, reflecting the possible compositions energetically favoring metallic glass formation. An optimized stoichiometry sub-region is further pinpointed, within which the driving force for glass formation is prominently larger than that outside. The present study evaluates glass formation in the Mg–Ni–Y system from two different perspectives, and the results have implications for the entire family of Mg-based systems. The prediction schemes could be of great help for guiding the composition design of ternary glass formers.

By applying a recently constructed interatomic potential, molecular dynamics (MD) simulations were performed to investigate the structural origin of chemical effects in Mg–Cu–Ni ternary metallic glasses. The detailed evolution of local atomic structure in a series of Mgx(Cu42.5Ni57.5)100−x (x = 40–80) metallic glasses was tracked and comprehensively characterized by the pair correlation function, Voronoi tessellation, Honeycutt–Andersen bond pair and local chemistry analyses. Remarkable topological short-range orders (SROs) were found in Mg–Cu–Ni metallic glasses, with the characteristic motifs being icosahedra. The degree of icosahedral ordering varies distinctly with the alloy composition and is intimately correlated with the phase stability of metallic glasses. In contrast to the long-term understanding that five-fold bond pairs are a direct indication of icosahedral ordering, it was revealed that bond pairs are actually insensitive to the composition, and whether icosahedral ordering is preferred or not, fragmented pentagonal bipyramids are always populated. Furthermore, it was indicated that multiple chemical interactions among constituent atoms do result in chemical SROs in Mg–Cu–Ni metallic glasses, which are characterized by enriched Mg atoms in neighboring shells than expected from the nominal composition. The atomic-scale topological or chemical heterogeneity helps tune the local environments in Mg–Cu–Ni metallic glasses to achieve efficient packing and energy minimization for various compositions.

Based on the Cu-Zr-Ti ternary phase diagram, four sets of Cu-Zr-Ti multilayered films with various compositions of Cu20Zr36Ti44, Cu36Zr31Ti33, Cu49Zr24Ti27, and Cu67Zr16Ti17 were prepared and then the ion beam mixing was carried out. It turned out that the increase of Cu content doesn’t always have a positive effect on the glass forming ability. The glass forming ability of Cu49Zr24Ti27 was degraded due to the appearance of a CsCl-type B2 structure CuZr phase in the eutectic region. The experimental observations justify the existence of the CuZr phase under the non-equilibrium condition. Possible formation mechanisms for the crystalline phase were also discussed in terms of the atomic collision theory.

Inherent hierarchical structure and its effect on shear localization were clarified for ternary Mg–Cu–Ni metallic glasses via molecular dynamics studies based on a newly constructed n-body potential for the system. Assisted by a proposed index to detect the medium-range correlation heterogeneity, it was found that the Cu/Ni-centered icosahedra and specific Mg-centered clusters exhibit a strong preference to interconnect, leading to the formation, over an extended scale, of a percolated network that serves as structural skeleton in the glassy matrix. In constituting the skeleton network, the clusters mainly integrate in an interpenetrating mode, while the noninterpenetrating linkages provide additional reinforcements, jointly consolidating the structural and energetic stability of the skeleton. Furthermore, by monitoring the structural evolution upon compressive deformation, it was revealed that the gradual collapse of the skeleton network is intimately correlated to the mechanical response of metallic glasses and acts as a structural signature of the initiation and propagation of shear bands.

By considering the different effects of enthalpies on the glass formation of ternary transition metal systems, a thermodynamic method is proposed to predict the glass-forming regions as well as the glass-forming abilities. Cu–Zr–Ti and ten more ternary systems, as well as the corresponding binary subsystems, were studied, and the predictions agree well with the experimental observations.

Six sets of the Fe–Ti–Nb multilayered films were first prepared and then subjected to ion beam irradiation with 180 keV Xe ions. The unique amorphous phases, phase separation induced dual amorphous phase and orientation-preferred BCC–Fe crystalline phase were observed in these Fe–Ti–Nb multilayered films at different irradiation doses. In addition, it is also revealed that the Ti-rich HCP crystalline phase could transform into a metastable FCC phase in the Fe15Ti75Nb10 film. The possible mechanisms of these non-equilibrium phase formation and structural transformations are discussed based on atomic collision theory, geometric crystallography and ab initio calculations.

•Glass formation range of the Ni–Ti–Ta system was predicted by thermodynamic calculation.•The metallic glasses could all be obtained in the five sets of Ni–Ti–Ta multilayered films by ion beam mixing.•The Ni42Ti36Ta22 was expected to be much more favorable for the amorphous phase formation.•The result of the experiment is quite compatible with the thermodynamic prediction.The glass formation range of the Ni–Ti–Ta system was predicted by thermodynamic calculation based on Miedema's model and Alonso's method. To verify the theoretical prediction, five sets of Ni–Ti–Ta multilayered films with various compositions which were located in the predicted glass formation range were designed and the ion beam mixing was carried out to synthesize the amorphous alloys in the Ni–Ti–Ta system. It turned out that in all the five films with overall compositions of Ni72Ti21Ta7, Ni60Ti28Ta12, Ni49Ti34Ta17, Ni42Ti36Ta22, and Ni29Ti46Ta25, amorphous phases were indeed obtained, showing a good agreement between the experimental results and the thermodynamic calculation. Besides, it is expected that the Ni42Ti36Ta22 was much more favorable for the amorphous phase formation.

•The phase formation and transformations induced by ion beam mixing were observed.•The addition of Y could extend the glass forming range of the Fe–Nb system.•When the addition of Y exceeded 42 at%, the glass forming ability would be deteriorated.Ion beam mixing experiments were carried out to investigate the effect of the Y addition on the glass forming ability and associated structural phase transformations of the Fe–Nb binary metal system. The results show that the addition of Y could extend the glass forming range of the Fe–Nb system from 25–75 at% Fe to 10–80 at% Fe, yet while the addition of Y exceeded 42 at%, the glass forming ability would be deteriorated. The effect of Y is considered to be attributed to the competition between the big size difference of the component metals and large positive heat of mixing of Y–Nb.

A realistic interatomic potential is constructed for the Al–Cu–Y system under a newly proposed formulism and applied to perform atomistic simulations, leading to predicting a hexagonal composition region within which metallic glass formation is energetically favored and the region is defined as the quantitative glass formation ability of the system. Amorphization driving force of a glassy alloy is then calculated to correlate the readiness of its forming ability in practice, and a local optimized stoichiometry is pinpointed to be Al74Cu14Y12, of which the metallic glass could be most stable or easiest obtainable. The predictions are well supported by the experimental observations reported so far in the literature. Further structural analysis indicates that adding Y extends the short-range landscape and facilitates developing a hybridized icosahedral- and fcc-like packing in the medium-range, eventually enhancing the glass formation ability of the system.

Cu13Zr40Al47 amorphous phase was obtained in the CuZrAl metallic system by 200 keV xenon ion beam mixing (IBM) in the irradiation range of 0.8∼4×1015 Xe+/cm2, clarifying that CuZAl metallic glasses with high concentration of Al could be experimentally obtained. We also found the mixtures of amorphous and crystalline phases newly formed in the Cu7Zr14Al79, Cu16Zr7Al77, Cu27Zr22Al51 and Cu84Zr9Al7 multilayered films. The possible formation mechanism of these resultant alloys is discussed in terms of the atomic collision theory. These experimental results also provide a substantial support to the results of molecular dynamics simulation, which presents a theoretical prediction of metallic glass favored region.Highlights► Metallic glasses and mixtures of amorphous and crystalline phases were synthesized in the Cu–Zr–Al system by ion beam mixing, ► There is a quite good agreement between experimental results and MD simulation and thermodynamic calculation.

•Amorphous alloys and composites were synthesized in Ni–Nb–Zr by ion beam mixing (IBM).•The formation mechanism of amorphous alloys and composites was discussed.•The IBM result is quite compatible with the observations of rapid solidification.Six sets of Ni–Nb–Zr multilayered films were designed and prepared with the overall compositions of Ni63Nb28Zr9, Ni48Nb13Zr39, Ni29Nb60Zr11, Ni79Nb12Zr9, Ni31Nb31Zr38, and Ni31Nb11Zr58, and an ion beam mixing experiment was then conducted using 180 keV xenon ions. It is found that the Ni–Nb–Zr system is a readily glass-forming system, and both fully amorphous alloys and amorphous–crystalline composites could be synthesized. A detailed discussion was presented for the formation mechanism of the amorphous alloys and amorphous–crystalline composites. In addition, thermodynamic calculation predicted the glass-forming ability of the system, which is in good agreement with the IBM results. The experimental results and thermodynamic calculation obtained in present study are also supported e.g. by the observations of rapid solidification.

Glass-forming ability/range of the Cu–Zr–Ni ternary system was studied by thermodynamic calculations and ion beam mixing of multilayered films. Thermodynamic calculations located an energetically favored composition region for metallic glass formation, and also characterized the composition dependence of the glass-forming ability. Under the guidance of the thermodynamics calculations, four sets of nano-sized Cu–Zr–Ni multilayered samples were designed, prepared and then subjected to irradiation by 200 keV xenon ions. It turned out that unique amorphous phases were indeed obtained in the samples Cu21Zr55Ni24 and Cu24Zr45Ni31 that were located in the predicted superior glass-forming ability region, while for the Cu33Zr17Ni50 and Cu68Zr19Ni13 samples that fell within the low glass-forming ability region, ion beam mixing resulted in the formation of amorphous-crystalline dual-phase structures. A brief discussion was also presented for the formation mechanisms of the amorphous phase and the amorphous-crystalline composites.

Four sets of ternary Ni-Nb-Ta multilayered samples with overall compositions of Ni69Nb8Ta23, Ni55Nb13Ta32, Ni42Nb16Ta42 and Ni29Nb18Ta53, respectively were prepared and subjected to 185 keV xenon ion beam mixing. The experimental results showed that in the four Ni-Nb-Ta multilayered samples, metallic glasses could all be obtained at appropriate doses, supporting the prediction directly from a proven realistic Ni-Nb-Ta interatomic potential through molecular dynamics simulations, and that two different atomic structures were observed, as in the corresponding selected area diffraction patterns, the locations of the diffused bands reflected from the metallic glass phases were observed at different angles for the Ni69Nb8Ta23 and Ni29Nb18Ta53 metallic glasses. Interestingly, Voronoi tellessation analysis indicated that the observed difference in atomic structures could be attributed to the distinct coordinate number spectra, i.e., the spectrum of the Ni69Nb8Ta23 metallic glass has its coordinate number (CN) equal to 13 as dominating atomic configuration (with a weight of about 27%), whereas for the Ni29Nb18Ta53 metallic glass, CN=14 is the dominating atomic configuration (also about 27%). Moreover, the distinct atomic configurations of the obtained Ni-Nb-Ta metallic glasses could be correlated to the structures of the constituent metals of the ternary Ni-Nb-Ta system, as the first neighbor of fcc is 12 and the sum of the first and second neighbors of bcc is 14, implying the structural heredity did play a role in metallic glass formation.

Based on the constructed Cu–Hf interatomic potential, Monte Carlo simulations were conducted to reveal the atomic configurations in heating and quenching of a CuHf2 alloy through scrutinizing the evolution of microchemical inhomogeneity. Simulations show that the CuHf2 crystalline structure becomes more homogeneous during heating but an obvious drop in microchemical inhomogeneity appears when reaching its melting point. During the quenching process, the CuHf2 melt becomes increasingly inhomogeneous and shows a change in the slope in the microchemical inhomogeneity around glass transition temperature. Simulation results were evidenced by the atomic packing analysis through the Voronoi tessellation method. The implications of our study suggest that the glass transition could be visualized as a process involving increase of microchemical inhomogeneity from the liquid to glassy state.

A unique face-centered-cubic (fcc) Zr-based solid solution was obtained in the Cu10Zr76Ni14 multilayered films upon 200 keV xenon ion beam mixing, accompanied by a novel phase transition sequence of Cu+Zr+Ni→dual-FCC→FCC→Amorphous while varying the irradiation dose. The energetic stability sequence, elastic stability and phonon behaviors derived from first-principle calculations jointly evidenced the metastability of fcc Zr from different perspectives. The experimental observations and theoretical calculations together justify the existence of an intermediate fcc Zr state under non-equilibrium conditions. Possible formation mechanisms for the metastable crystalline phase were also discussed in terms of the atomic collision theory.Highlights► Existence of an intermediate fcc Zr state under non-equilibrium conditions was justified. ► A new metastable Zr-based fcc phase was obtained in the Cu10Zr76Ni14 multilayered films. ► A novel transition sequence was observed and discussed via thermodynamics and kinetics. ► Metastability of fcc Zr was verified by first-principle calculations from various perspectives. ► Possible mechanisms for the metastable phase formation were discussed.

In the ion beam mixing experiments, eight Fe-Hf-Nb multilayered films, with overall compositions of Fe67Hf22Nb11, Fe67Hf11Nb22, Fe54Hf38Nb8, Fe54Hf30Nb16, Fe54Hf11Nb35, Fe25Hf67Nb8, Fe25Hf50Nb25 and Fe25Hf11Nb64, were irradiated by 200 keV xenon ions to doses ranging from 3×1014 Xe+/cm2 to 7×1015 Xe+/cm2. The results showed that unique amorphous phases were obtained at designed alloy compositions, falling in the favored glass-forming region deduced from three binary metal sub-systems. Interestingly, at some alloy compositions, the crystal-amorphous-crystal transformations were observed back and forth while varying the irradiation doses. In addition, at the alloy composition of Fe25Hf67Nb8, a metastable FCC phase was formed through an HCP-FCC structural phase transformation and it had a large lattice constant identified to be a=4.51 Å. Besides, the formation mechanism of non-equilibrium alloy phases was also discussed in terms of thermodynamics of solids and atomic collision theory.

Glass forming ability of the ternary Ni-Nb-Mo system was studied by ion beam mixing of the Ni-Nb-Mo multilayered films. In the experiment, metallic glasses i.e. amorphous alloys were formed in the Ni51Nb19Mo30, Ni52Nb35Mo13, Ni61Nb15Mo24 and Ni72Nb20Mo8 multilayered films, while only solid solutions were obtained in the Ni24Nb29Mo47 and Ni26Nb53Mo21 multilayered films. It turned out that the Ni concentration played a dominating role in affecting the glass-forming ability of the system. Besides, thermodynamic calculations predicted a favored composition region for metallic glass formation, matching well with the observations from ion beam mixing.

Over one hundred and thirty Pd–Zr intermetallic compounds, including stable and hypothetical ones, are first identified, then the corresponding physical properties such as formation enthalpies, elastic constants and bulk modulus are investigated by ab initio calculations. Based on the calculated formation enthalpies of these Pd–Zr compounds with a variety of structures and different compositions, the ground-state convex hull is derived for the Pd–Zr system. It also turns out that most of the calculated results match well with the available experimental observations. Therefore, the calculated results of stable and hypothetical phases can provide a basis for further thermodynamic calculations and atomistic simulations. Interestingly, it is found that the formation enthalpies of these compounds approximately vary linearly with the atomic volumes for Pd–Zr compounds. In addition, due to the anharmonicity of interatomic interaction, the bulk modulus of these compounds exhibit a negative linear correlation with the atomic volumes, i.e. phases with small atomic volumes usually have large bulk modulus.Highlights► Formation enthalpies and structures of 133 Pd–Zr compounds are studied by ab initio. ► The ground-state convex hulls are outlined for the Pd–Zr system. ► There are linear correlations among the calculated structural properties.

For the Fe–Zr–Nb system, ion beam mixing of multiple metal layers with various compositions was carried out. Using high resolution transmission electron microscopy analyses, nine compositions were determined to be favored for metallic glass formation. It is found that all these composition points fall in a hexagonal region defined by linearly connecting the six composition points determining the glass-forming ranges of its sub-binary systems. It is therefore proposed to predict the favored glass-forming region for a ternary metal system by the glass-forming ranges of its sub-binary systems.Highlights► Metallic glasses were formed by ion beam mixing in Fe–Zr–Nb multilayered films. ► Phase separations were observed in some multilayered films. ► A method is proposed to predict the glass-forming region of a ternary metal system.

For the Cu–Zr–Al system, the glass forming compositions were firstly calculated based on the extended Miedema's model, suggesting that the amorphous phase could be thermodynamically favored over a large composition region. An n-body potential was then constructed under the smoothed and long-range second-moment-approximation of tight-binding formulism. Applying the constructed Cu–Zr–Al potential, molecular dynamics simulations were conducted using solid solution models to compare relative stability of crystalline solid solution versus its disordered counterpart. Simulations reveal that the physical origin of metallic glass formation is crystalline lattice collapsing while solute concentration exceeding the critical value, thus predicting a hexagonal composition region, within which the Cu–Zr–Al ternary metallic glass formation is energetically favored. The molecular dynamics simulations predicted composition region is defined as the quantitative glass-forming-ability or glass-forming-region of the Cu–Zr–Al system.

In the Fe–Rh system, the Fe100 − xRhx (x = 40, 50, 65, 70, and 90) multilayered films were prepared and then subjected to ion beam mixing using 200 keV Xe ions. Upon ion beam mixing, amorphous alloy was obtained in the Fe70Rh30 sample, in which an interesting phase transition path was observed as Fe + Rh → fcc → fcc + a → fcc + bcc → fcc. In addition, a new metastable crystalline fcc phase was observed in the Fe50Rh50 sample together with the solid solutions, and the lattice constants of the ion mixed phases were consistent with those from ab initio calculations. Possible mechanisms for the formation of both amorphous and metastable crystalline phases are discussed in terms of the atomic collision theory.

A new metastable crystalline phase of bcc structure was obtained in the Mo–Pd system by 200 keV xenon ion beam mixing in the Mo34Pd66 and Mo30Pd70 multilayered thin films at relevant irradiation stages and its lattice constant was identified to be aBCC = 4.13 Å. The real composition of the bcc phase was then estimated to be around MoPd2. The newly formed intermetallic compound with bcc structure gives evidence that MoPd2 could be an ordered intermetallic phase in the binary phase diagram. The possible formation mechanism of the metastable MoPd2 bcc phase was also discussed in terms of the atomic collision theory.Highlights► A novel metastable crystalline phase was obtained in the Mo-Pd system by 200 keV xenon ion beam mixing. ► The newly formed phase was confirmed to have an bcc structure and a composition around MoPd2. ► The new bcc metastable crystalline complement the former experimental and calculated phase diagram of Mo-Pd system.

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.

For the Cu−Zr−Ni system, an interatomic potential was constructed under the newly proposed formulism named smoothed and long-range second-moment approximation of tight-binding. Applying the constructed potential, molecular dynamics simulations were carried out to compare the relative stability of crystalline solid solution versus its disordered counterpart. Simulations not only reveal that the origin of metallic glass formation is the crystalline lattice collapsing while the solute concentrations exceed critical values, but also determine a quadrilateral region, within which the metallic glass formation is energetically favored. Moreover, the energy differences between the crystalline solid solutions and the disordered states were considered as the driving force for amorphization and were computed by molecular static calculations. The calculation results located an optimized composition area with the driving force much greater than those outside. In addition, the alloys around the composition of Cu16Zr60Ni24 were identified to have maximum driving force, and the atomic configurations were also analyzed by the Voronoi tessellation method.

Based on Miedema's semi-empirical model, a Gibbs free energy diagram is constructed for the Cu–Hf system and shows that the amorphous phase is favored to be formed over 8–94 at.% Hf, which is much broader than the experimentally determined 30–70 at.% Hf. Three Cu–Hf multilayered films were therefore designed with the overall compositions of Cu93Hf7, Cu81Hf19 and Cu23Hf77, respectively, and then an ion beam mixing experiment was conducted using 200 keV xenon ions to see whether the metallic glass forming range of the Cu–Hf system could be extended beyond the previously reported range. Interestingly, ion beam mixing results show that a uniform amorphous phase can be obtained in the Cu23Hf77 sample and the amorphous phase is also observed to coexist with crystalline Cu in the Cu81Hf19 sample. These results suggest that the metallic glass forming range of the Cu–Hf system could, at least, be extended to 77 at.% Hf, which falls in the range predicted by the Gibbs free energy diagram.

An ion beam mixing experiment for Cu–Zr system was conducted and two supersaturated solid solutions were observed with compositions of 16 atom% Zr in Cu and 17 atom% Cu in Zr, respectively, which are much greater than almost nil found from the equilibrium phase diagram of Cu–Zr system. The observation indicates that Cu–Zr metallic glasses could possibly be obtained in composition range bounded by the two observed solid solubilities, i.e. 16–83 atom% Zr. Besides, a unique Cu65Zr35 metallic glass was obtained by ion beam mixing and its composition is very close to the so-called best composition referred in the literature.

Ta-rich and a Ag-rich solid solutions, both of face-centered cubic (fcc) structures, are observed in the Ag14Ta86 multilayered films on 200-keV xenon ion beam mixing, and the formation of two co-existing solid solutions is the result of a process of spinodal decomposition. The abnormal fcc Ta-rich solid solution has a Ta concentration larger than 86 at. pct and a lattice constant determined to be around 4.28 Å. Besides, first-principles calculations were employed to understand the possibility of a structural phase transition from body-centered cubic to fcc in Ta. Comparing the heat of formation (ΔHf) differences between fcc and bcc structures, Ta has the smallest ΔHf difference among the four refractory metals (Ta, Mo, Nb, and W). It is concluded that the interfacial and irradiation energies play important roles in overcoming the energy barrier for the structural phase transition to take place.

An n-body potential is constructed for the Cu−Ti−Hf ternary metal system under a recently proposed formalism named long-range empirical potential. Applying the proven relevant Cu−Ti−Hf potential, molecular dynamics simulations are carried out using solid solution model to compare the relative stability of the crystalline solid solution versus its disordered counterpart as a function of solute concentration. The simulation results not only reveal that the physical origin of the crystal-to-amorphous transition is the collapse of the crystalline lattice, while the solute atoms exceed the critical value, but also predict a region in the composition triangle energetically favored for the Cu−Ti−Hf ternary metallic glass formation. Interestingly, the prediction directly from the n-body potential is supported by the experimental observations and is in accordance with the so-called structural difference rule.

By considering the energetic competition between the crystalline solid solution and glass phase, a thermodynamic method is proposed to predict/determine the glass forming range of a ternary metal system and in terms of the dynamics, the parameter γABC* is further defined to search for a proper alloy with superior glass forming ability in the system. 10 more ternary/binary metal systems, e.g. the Cu–Zr–Ti and Cu–Hf–Ti systems, were studied and the predicted alloys of superior glass forming ability match well with those reported from experimental observations.

Multilayered films of Rh1−xTax (x = 25, 40, 50, 60) were prepared and irradiated by 200 keV Xe+. A Gibbs free energy diagram of the Rh–Ta system was derived that predicted the glass-forming range to be within 43–65 at.% of Ta. This agreed well with the experimental results. An interest phase transformation mechanism of Rh + Ta → fccI + fccII → fcc was observed and discussed.

Within the framework of the second-moment approximation of the tight-binding theory, n-body potentials are proposed for hcp, fcc and bcc transition metals and their alloys. Both the energies and their derivatives calculated from the proposed potentials go smoothly to zero at cutoff radii, thus avoiding the unphysical behaviors that may emerge in simulations. With the assistances of ab initio calculations, the proposed potentials are then applied to Zr, Hf, Cu, V, Nb, Ta and their binary alloys. It turns out that the n-body potentials can well predict the energy sequence of stable and metastable structures of these metals. The vacancy formation energies, surface energies and melting points derived from the potentials also match well with experimental results. Based on the constructed potentials, molecular dynamics simulations reveal that Cu–Nb and Zr–Nb metallic glasses could be formed within the composition range of about 15–72 and 8–80 at.% Nb, respectively, matching well with experimental observations. Voronoi analyses reveal that the dominating atomic packings in Cu–Nb metallic glasses are the icositetrahedron (CN = 14), icosihexahedron (CN = 15) and icosidihedron (CN = 13) with fractions of 33%, 26% and 21%, respectively.

Based on Miedema’s method for binary alloys, a thermodynamic model is proposed for calculating the standard formation enthalpies of ternary alloy systems. In the proposed model, both the atomic size difference of the constituent metals and the interaction between the third metal and the other two are taken into account. Compared with the Miedema’s original model, the newly proposed model can considerably improve the precision of calculation.

Under the framework of the Vienna ab initio simulation package, calculation results predicted that two energetic metastable states with either D019 or L12 structure were favored near the compositions of Ni3Ru and NiRu3, respectively, in the Ni–Ru system characterized by a positive heat of formation. Applying a far-from-equilibrium scheme of ion mixing, an hcp and an fcc metastable phases were indeed formed in the Ni75Ru25 and Ni25Ru75 multilayers, respectively, upon xenon ion irradiation at 77 K and their lattice constants determined by means of diffraction analysis were in good agreement with those from ab initio calculation.

In the equilibrium immiscible Fe–Cu system, self-avoiding chains of ferromagnetic polycrystalline Fe grains were grown in the Fe50Cu50 multilayers after 200 keV xenon ion irradiation at room temperature to a dose of 5×1015 Xe+ cm−2 and the chains featured self-similarity with a fractal dimension of 1.42. Increasing the irradiation dose up to 1×1016 Xe+ cm−2 induced the Fe grains to organize themselves into a branching tree morphology with an increased fractal dimension of 1.88. In contrast, a new non-fractal pattern consisting of fcc Cu-rich grains was developed in the Fe30Cu70 multilayered films at an irradiation dose of 1×1016 Xe+ cm−2 and was named as earthworm-like pattern. It is thought that the observed patterns were grown during the relaxation period immediately after the atomic collision cascade triggered by ion irradiation and that the pattern selection is determined by the combining effects of magnetic and repulsive interactions among the aggregating particles of either Fe or Cu grains.

Anomalous structural evolution was observed in an equilibrium immiscible Co–Cu system while the Co–Cu multilayers were irradiated by Xenon ions at 77 K. In the as-deposited Co15Cu85 multilayers consisting of polycrystalline Co and Cu of fcc structure, 100 keV Xenon ion irradiation to a dose of resulted in amorphization and the formation of a new dodecagonal phase embedded in the amorphous matrix. In another sample with an overall composition of Co35Cu65, the same dodecagonal phase was also obtained by 200 keV Xenon ion irradiation within a dose range of and interestingly, the formed dodecagons assembled themselves in a superlattice with an in-plane four-fold rotational symmetry. According to the non-equilibrium characteristics involved in ion irradiation process, the mechanism of the above structural evolution is discussed in terms of the similarity in the atomic configuration between the quasicrystal and amorphous short-range orders as well as the effect of interfacial free energy stored in the Co–Cu multilayers.

Using a metal vapor vacuum arc (MEVVA) ion source, metallic silicides, such as C54-TiSi2, NiSi2, COSi2, NbSi2 and TaSi2, etc., with good electrical properties were obtained directly on Si wafers by high current metal-ion implantation with neither in situ heating nor post-annealing. Semiconducting silicides, such as β-FeSi2 and CrSi2, were also directly formed on Si wafers by MEVVA ion implantation with unique physical properties. The growth mechanism of the metal silicides is also discussed for Ni–Si as a representative system.

Sequential disordering of the original Ni and Nb crystalline lattices in the as-deposited Ni–Nb multilayers was observed, for the first time, in the early stage of solid-state interfacial reaction conducted on a hot-stage in a transmission electron microscope. It was the origin of a predicted or observed asymmetric growth of amorphous interlayer in solid-state amorphization in some binary metal systems. The interfacial reaction proceeds with increasing annealing temperature and time, and solid-state amorphization eventually dominates in the Ni48Nb52 multilayers, whereas a new HCP metastable crystalline phase was obtained in the Ni70Nb30 multilayers. A reasonable interpretation to the formation of the amorphous and HCP phases is given by a calculated Gibbs-free-energy diagram of the Ni–Nb system.

The present article focuses on a discussion concerning the concept, method and detailed construction procedure of seven interatomic potentials currently available for fcc, bcc and hcp transition metals and their binary alloys. The potentials include the embedded atom method potential and its modified version, in which the cross-potential takes a three-parameter linear function, the second-moment approximation of tight-binding potential and its smoothed version, in which a truncation function is incorporated to improve the performance, the Finnis–Sinclair potential and its extended version, in which the atomic interaction is strengthened, and the recently proposed long-range empirical potential. Meanwhile, an important method, i.e.ab initio assisted construction of interatomic potentials, is introduced and the method is necessary whenever the physical data are lacking in fitting potentials. Moreover, applications of some twenty constructed potentials for studying materials science related issues are presented, such as the structural phase transitions, characteristics of metastable alloys, atomic structure of metallic glasses, and solid-state interfacial reaction/amorphization.

•Unique amorphous phases could be formed in all the studied Fe(HfxTa1−x) films.•BCC-Hf phase formation and preferred orientation were observed in Fe50Hf50 films.•Good soft magnetic properties were observed in the amorphous films obtained.Metastable phase formation and magnetic properties of the Fe50(HfxTa1−x)50 (x = 0, 0.2, …, and 1) thin films induced by ion beam mixing are studied. The results show that unique amorphous phases could be formed in all the six multilayered films. Interestingly, preferred orientations and formation of BCC-Hf phase were observed in the Fe50Hf50 multilayered films at as-deposited state and after irradiated to doses less than 6 × 1014 Xe+/cm2. In addition, good soft magnetic properties were obtained in the formed amorphous phases. The Fe50Hf40Ta10 amorphous phase owns the maximum magnetization of 45 emu/g (i.e., 1.21 μB per Fe atom) at 5 K, with a saturate magnetization of 7.5 emu/g and a small coercivity Hc = 7 Oe at room temperature. The possible mechanisms responsible for the observations are discussed in terms of atomic collision theory and crystallography.

By considering the energetic competition between the crystalline solid solution and glass phase, a thermodynamic method is proposed to predict/determine the glass forming range of a ternary metal system and in terms of the dynamics, the parameter γABC* is further defined to search for a proper alloy with superior glass forming ability in the system. 10 more ternary/binary metal systems, e.g. the Cu–Zr–Ti and Cu–Hf–Ti systems, were studied and the predicted alloys of superior glass forming ability match well with those reported from experimental observations.

With the aid of ab initio calculations, a realistic interatomic potential was constructed for the Mg–Cu–Y ternary system under the proposed formalism of smoothed and long-range second-moment approximation of tight-binding. Taking the potential as the starting base, an atomistic computation/simulation route was developed for designing favored and optimized compositions for Mg–Cu–Y metallic glass formation. Simulations revealed that the physical origin of metallic glass formation is the collapse of crystalline lattice when solute concentration exceeds a critical value, thus leading to predict a hexagonal region in the Mg–Cu–Y composition triangle, within which metallic glass formation is energetically favored. It is proposed that the hexagonal region can be defined as the intrinsic glass formation region, or quantitative glass formation ability of the system. Inside the hexagonal region, the driving force for formation of each specific glassy alloy was further calculated and correlated with its forming ability in practice. Calculations pinpointed the optimized stoichiometry in the Mg–Cu–Y system to be Mg64Cu16Y20, at which the formation driving force reaches its maximum, suggesting that metallic glasses designed to have compositions around Mg64Cu16Y20 are most stable or easiest to obtain. The predictions derived directly from the atomistic simulations are supported by experimental observations reported so far in the literature. Furthermore, Honeycutt–Anderson analysis indicated that pentagonal bipyramids (although not aggregating to form icosahedra) dominate in the local structure of the Mg–Cu–Y metallic glasses. A microscopic picture of the medium-range packing can then be described as an extended network of the pentagonal bipyramids, entangled with the fourfold and sixfold disclination lines, jointly fulfilling the space of the metallic glasses.

Inherent hierarchical structure and its effect on shear localization were clarified for ternary Mg–Cu–Ni metallic glasses via molecular dynamics studies based on a newly constructed n-body potential for the system. Assisted by a proposed index to detect the medium-range correlation heterogeneity, it was found that the Cu/Ni-centered icosahedra and specific Mg-centered clusters exhibit a strong preference to interconnect, leading to the formation, over an extended scale, of a percolated network that serves as structural skeleton in the glassy matrix. In constituting the skeleton network, the clusters mainly integrate in an interpenetrating mode, while the noninterpenetrating linkages provide additional reinforcements, jointly consolidating the structural and energetic stability of the skeleton. Furthermore, by monitoring the structural evolution upon compressive deformation, it was revealed that the gradual collapse of the skeleton network is intimately correlated to the mechanical response of metallic glasses and acts as a structural signature of the initiation and propagation of shear bands.

An interatomic potential was constructed for the Ni–Zr–Mo ternary metal system with the newly proposed long-range empirical formulism, which has been verified to be applicable for fcc, hcp and bcc transition metals and their alloys. Applying the constructed potential, molecular dynamics simulations predict a hexagonal composition region within which metallic glass formation is energetically favored. Based on the simulation results, the driving force for amorphous phase formation is derived, and thus an optimized composition is pinpointed to Ni45Zr40Mo15, of which the metallic glass could be most stable or easiest to obtain. Further structural analysis indicates that the dominant interconnected clusters for Ni64Zr36−xMox MGs are 〈0, 0, 12, 0〉, 〈0, 1, 10, 2〉, 〈0, 2, 8, 2〉 and 〈0, 3, 6, 4〉. In addition, it is found that the appropriate addition of Mo content could not only make a more ordered structure with a higher atomic packing density and a lower energy state, but also improve the glass formation ability of Ni–Zr–Mo alloys. Moreover, inherent hierarchical atomic configurations for ternary Ni–Zr–Mo metallic glasses are clarified via the short-range, medium-range and further in the extended scale of the icosahedral network.

Based on the constructed Cu–Hf interatomic potential, Monte Carlo simulations were conducted to reveal the atomic configurations in heating and quenching of a CuHf2 alloy through scrutinizing the evolution of microchemical inhomogeneity. Simulations show that the CuHf2 crystalline structure becomes more homogeneous during heating but an obvious drop in microchemical inhomogeneity appears when reaching its melting point. During the quenching process, the CuHf2 melt becomes increasingly inhomogeneous and shows a change in the slope in the microchemical inhomogeneity around glass transition temperature. Simulation results were evidenced by the atomic packing analysis through the Voronoi tessellation method. The implications of our study suggest that the glass transition could be visualized as a process involving increase of microchemical inhomogeneity from the liquid to glassy state.

For the Cu–Zr–Al system, the glass forming compositions were firstly calculated based on the extended Miedema's model, suggesting that the amorphous phase could be thermodynamically favored over a large composition region. An n-body potential was then constructed under the smoothed and long-range second-moment-approximation of tight-binding formulism. Applying the constructed Cu–Zr–Al potential, molecular dynamics simulations were conducted using solid solution models to compare relative stability of crystalline solid solution versus its disordered counterpart. Simulations reveal that the physical origin of metallic glass formation is crystalline lattice collapsing while solute concentration exceeding the critical value, thus predicting a hexagonal composition region, within which the Cu–Zr–Al ternary metallic glass formation is energetically favored. The molecular dynamics simulations predicted composition region is defined as the quantitative glass-forming-ability or glass-forming-region of the Cu–Zr–Al system.