Shuqing Zhao

Atomistic approach to design favored compositions for the ternary Al–Mg–Ca metallic glass formation

An interatomic potential is first constructed for the Al–Mg–Ca system under the formalism of long-range smoothed second-moment approximation of tight-binding scheme, and then applied in Monte Carlo simulations to compare the relative stability of a crystalline solid solution versus its disordered counterpart using solid solution models. Simulation results not only predict a glass formation region (GFR), within which the Al–Mg–Ca metallic glass formation is energetically favoured, but also derive the amorphisation driving force (ADF), i.e., the energy difference between the solid solution and disordered state. The ADF is proposed to be positively correlated to the glass forming ability (GFA), suggesting that the larger the ADF is, the easier it is to produce the amorphous alloy and the more stable it is. Moreover, Voronoi tessellation analysis shows a distinct arrangement of Al (Mg, Ca)-centered cluster, correlating closely to the atomic radii and the formation energy of the components. The predictions are fairly consistent with the experimental results reported so far.

Computational assisted design of the favored composition for metallic glass formation in a Ca–Mg–Cu system

To well predict the favored composition for metallic glass formation in a Ca–Mg–Cu system, a realistic interatomic potential was first constructed for the system and then applied to Monte Carlo simulations. The simulation not only predicts a hexagonal composition region for metallic glass formation, but also provides a favored sub-region within which the amorphization driving force is larger than that outside. The simulations show 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 1551 bond pairs (icosahedral-like) dominate in the favored sub-region. The large atomic size difference between Ca, Mg, and Cu extends the short-range landscape, and a microscopic image of the medium-range packing can be described as an extended network of pentagonal bipyramids entangled with four-fold and six-fold disclinations, together fulfilling the space of the metallic glasses. The predictions are well supported by the experimental observations reported to date and can provide guidance for the design of ternary glasses.

The optimized composition of Mg–Al–Cu metallic glass investigated by thermodynamic calculations and an atomistic approach

Issues related to the glass formation of ternary Mg–Al–Cu metallic glass are investigated by thermodynamic calculations and an atomistic approach. Based on the extended Miedema model, thermodynamic calculations show that Mg–Al–Cu metallic glasses are favored over a large composition range, and that the sub-region of MgxAlyCu1−x−y (x = 20–30; y = 30–40; 1 − x − y = 35–45) shows a better glass formation ability than the other compositions. Then, a realistic interatomic potential was constructed for the Mg–Al–Cu system and applied in Monte Carlo simulations to predict the favored composition at the atomic level, and even pinpoint the optimized composition. The simulation not only predicted a quadrilateral region, within which Mg–Al–Cu metallic glass formation is energetically favored, but also pinpointed an optimized sub-region within which the amorphization driving force (ADF), i.e. the energy difference between the solid solution and the disordered state, is larger than that outside. The predictions of the atomistic approach are consistent with the thermodynamic calculation. The simulations not only provided predictions for producing Mg–Al–Cu metallic glasses, but also revealed the physical origin of the crystal–amorphous transition, which could be of great help for designing ternary glass formers.