Bulk Metallic Glasses XIX: Atomistic Simulations, Modelling and Theory
Sponsored by: TMS Structural Materials Division, TMS: Mechanical Behavior of Materials Committee
Program Organizers: Robert Maass, Federal Institute of Materials Research and Testing (BAM); Peter Derlet, Paul Scherrer Institut; Katharine Flores, Washington University in St. Louis; Yonghao Sun, Chinese Academy of Sciences; Lindsay Greer, University of Cambridge; Peter Liaw, University of Tennessee
Tuesday 2:30 PM
March 1, 2022
Room: 253C
Location: Anaheim Convention Center
Session Chair: Yuanchao Hu, Yale University
2:30 PM Invited
Atomic Cooperativity in Metallic Glass: Takeshi Egami1; 1University of Tennessee
Mechanical deformation and atomic transport in metallic glasses are controlled by atomic cooperativity, but the nature of cooperativity has been debated. The leading idea is that some soft region, such as distributed free-volume, defines the cooperativity. I propose an opposite view, that the cooperative resistance to atomic motion, hardness, determines atomic transport. The scale of cooperativity is represented by the coherence length of the medium-range order (MRO). We show that the activation energy for motion in supercooled liquid and liquid fragility are proportional to the coherence volume. Defect-like sites, soft spots, may initiate local atomic movements, but the defect structure disappears during the motion. At the saddle-point of the potential energy landscape the memory of prior thermal history is lost by configurational melting. What determines the outcome is not where the movement started, but how it is resisted by the organization of the system. The work is supported by DOE-BES.
2:55 PM
Chemical and Topological Frustration in Binary Metallic Glass Formation: Yuanchao Hu1; Jan Schroers1; Mark Shattuck2; Corey O'Hern1; 1Yale University; 2The City College of New York
Although many thermodynamic parameters have been correlated with glass-forming ability (GFA), a comprehensive understanding of the microscopic mechanisms for GFA is still lacking. In recent studies, we performed large-scale molecular dynamics simulations of Lennard-Jones systems to investigate the effects of several elemental features, including cohesive energy, atomic symmetry, and size ratio, on glass formation in binary alloys. We find that topological frustration, like locally favored icosahedral structures, contributes to glass formation, but these structures also promote quasi-crystal formation. More importantly, we find that the amount of chemical frustration, characterized by the degree to which local concentration of different atom types deviates from that in the liquid state, provides an accurate prediction of the GFA. In addition, we describe a new mechanism of bond shortening that can explain the GFA of many alloys. We anticipate that our findings will also be relevant for understanding the GFA in ternary and multicomponent alloys.
3:15 PM
Evidence of Crystalline Phase Precursors within High-temperature Metallic Liquids and their Effect on Glass-forming Ability: Porter Weeks1; Katharine Flores1; 1Washington University in St Louis
While much research has focused on the evolution of structure within high-temperature and undercooled metallic liquids, the general lack of an effective technique to quantitatively describe the atomic-scale structure of the liquid has made its correlation with lower temperature phenomena extremely challenging. Here, we apply a machine learning-based approach to identify and analyze atomic clusters in a variety of simulated binary (Cu-Zr, Ni-Nb, Ni-Zr) and ternary (Al-Ni-Zr) liquids. We show that the structure within the high-temperature liquid yields clear evidence of precursors for the low-temperature crystalline phases. We propose that there are two criteria for glass-forming ability (GFA): a lack of order within the liquid state, as quantified by the population distribution of atomic clusters, and a general lack of similarity of those structures to stable or metastable crystalline phases. This research suggests that a significant amount of information regarding GFA is buried within the structure of the high-temperature liquid.
3:35 PM
Hall-Petch-like Relationship in Metallic Glasses: Yucong Gu1; Lin Li1; Xiao Han1; Feng Yan1; 1University of Alabama
Metallic glasses (MGs) have high strength but minimal ductility. To improve ductility, it is suggested that tuning the nanoscale heterogeneity can be exploited to distribute localized flow. In this study, a mesoscale shear transformation zone dynamics model has been developed by incorporating elastic and plastic heterogeneities of deformation units in CuZr MGs. The spatial correlation of elastic heterogeneity leads to the formation of nanoscale soft spots that exhibit a great propensity to carry the plastic flow. The modeling results reveal a Hall-Petch-like relationship between the yield stress and spatial correlation length of heterogeneity. Furthermore, the slope of the Hall-Petch relationship scales with the standard deviation of the elastic heterogeneity. From modeling data, a multivariate nonlinear regression composite function is derived and used to explain the experimental results of MGs with various heterogeneities. The regression function can be further applied to guide the design of the nanoscale heterogeneity in amorphous nanostructures.
3:55 PM Discussion on atomistic simulations, modelling, and theory of metallic glasses