Cluster-assembled metallic glasses

Atomic-Approach to Predict the Energetically Favored Composition Region and to Characterize the Short-, Medium-, and Extended-Range Structures of the Ti-Nb-Al Ternary Metallic Glasses

Ab initio calculations were conducted to assist the construction of the n-body potential of the Ti-Nb-Al ternary metal system. Applying the constructed Ti-Nb-Al interatomic potential, molecular dynamics and Monte Carlo simulations were performed to predict a quadrilateral composition region, within which metallic glass was energetically favored to be formed. In addition, the amorphous driving force of those predicted possible glassy alloys was derived and an optimized composition around Ti₁₅Nb₄₅Al₄₀ was pinpointed, implying that this alloy was easier to be obtained. The atomic structure of Ti-Nb-Al metallic glasses was identified by short-, medium-, and extended-range analysis/calculations, and their hierarchical structures were responsible to the formation ability and unique properties in many aspects.

Atomistic modeling to investigate the favored composition for metallic glass formation in the Ca-Mg-Ni ternary system

A realistic interatomic potential was first constructed for the Ca-Mg-Ni system and then applied to Monte Carlo simulations to predict the favored composition for metallic glass formation in the ternary system. The simulations not only predict a hexagonal composition region, within which the Ca-Mg-Ni metallic glass formation is energetically favored, but also pinpoint an optimized sub-region within which the amorphization driving force, i.e. the energy difference between the solid solution and disordered phase, is larger than that outside. The simulations further reveal that the physical origin of glass formation is the solid solution collapsing when the solute atom exceeds the critical solid solubility. Further structural analysis indicates that the pentagonal bi-pyramids dominate in the optimized sub-region. The large atomic size difference between Ca, Mg and Ni extends the short-range landscape and facilitates the development of a hybridized packing model in the medium-range, and eventually enhancing the glass formation in the system. The predictions are well supported by the experimental observations reported so far, and could be of help for designing the ternary glass formation.

Structural skeleton of preferentially interpenetrated clusters and correlation with shear localization in Mg-Cu-Ni ternary 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.

Favored composition design and atomic structure characterization for ternary Al-Cu-Y metallic glasses via proposed interatomic potential

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.