Bulk Metallic Glasses XVIII: Structures and Characterization
Sponsored by: TMS Structural Materials Division, TMS: Mechanical Behavior of Materials Committee
Program Organizers: Peter Liaw, University of Tennessee; Yanfei Gao, University of Tennessee-Knoxville; Hahn Choo, University of Tennessee; Yunfeng Shi, Rensselaer Polytechnic Institute; Robert Maass, Federal Institute of Materials Research and Testing (BAM); Xie Xie, FCA US LLC; Gongyao Wang, Globus Medical
Wednesday 8:30 AM
March 17, 2021
Room: RM 7
Location: TMS2021 Virtual
Session Chair: Robert Maass, Federal Institute of Materials Testing and Research; Joerg Loeffler, ETH Zurich
8:30 AM Invited
Ultrafast-calorimetry Experiments to Study Multistep Crystallization and Melting Pathways in Metals: Jörg Löffler1; 1ETH Zurich
Studying phase transitions and metastable phase formation in metals is generally difficult because of their rapid nucleation and growth kinetics. However, when applying fast differential scanning calorimetry (FDSC) to slowly transforming bulk metallic glasses, we can explore new phase transition pathways and study the sequences of metastable phase formation. Applying FDSC, we can also explore novel glass states and determine their stochastics of nucleation [1]. Via rapid heating we are further able to surpass metastable-to-stable solid phase transitions, and thus isolate and melt the metastable phases to determine their thermophysical properties in detail. In this way we can study multistep crystallization and melting pathways in metals, and construct the corresponding energy-temperature diagrams including metastable phases [2]. In fact, we show that even simple binary alloys can reveal multiple melting points. [1] J.E.K. Schawe, J.F. Löffler, Nature Comm. 10, 1337 (2019).[2] G. Kurtuldu, J.F. Löffler, Adv. Science 7, 1903544 (2020).
8:55 AM Invited
Tracing Structural Dynamics in Metallic Glasses during Cryogenic Cycling: Amlan Das1; Eric Dufresne2; Robert Maass3; 1University of Illinois at Urbana-Champaign; 2Argonne National Laboratory; 3Federal Institute for Materials Research and Testing (BAM)
Metallic glasses relax continuously with time and methods to uniformly rejuvenate the material are needed. One promising avenue is cryogenic-cycling, but the fundamental structural processes induced by this method are not well understood. In order to shed more light onto the structural processes of cryogenic cycling, we pursue in-situ x-ray photon correlation spectroscopy to trace the atomic-scale structural dynamics of a Zr-based metallic glass. This method allows calculating the relaxation times as a function of time in-situ during thermal cycling. It is found that cryogenic cycling homogenizes the relaxation time distribution. We furthermore reveal how fast atomic-scale dynamics is correlated with long-time structural relaxation times, and that fast atomic-scale relaxation are more prominent in rapidly quenched ribbons than in a bulk plate material. Overall, a picture emerges that points towards heterogeneities in fictive temperature as a requirement for cryogenic energy storage.
9:20 AM
The Secondary Phase of Bulk Metallic Glass: Sydney Corona1; Seola Lee1; Celia Chari1; Jong Hyun Na2; Konrad Samwer3; William Johnson1; 1California Institute of Technology; 2Glassimetal Technologies; 3University of Göttingen
Bulk Metallic Glasses (BMGs) – traditionally understood as a single-phase disordered glass – have been found to display a liquid-liquid (glass-glass) phase transition. This transition leads to growth of secondary phase glassy inclusions upon annealing of as-quenched glasses, with discontinuous properties across the interface. The presented study identifies and characterizes the secondary glass phase in several exemplary metallic glass systems. The inclusions show a 20% hardness increase from the matrix, Energy Dispersive Spectroscopy (EDS) reveals compositional equivalence of the two phases, and dark-field Transmission Electron Microscopy (TEM) characterizes the dual amorphous character.
9:40 AM
Fragility, Medium Range Order and Boson Peak in Liquids: Chae Woo Ryu1; Takeshi Egami1; 1University of Tennessee
Viscosity varies by an enormous amount, from the order of 10-3Pa.s at high temperatures to 1012Pa.s at Tg. The rate of this change near Tg defines fragility, which varies widely for different materials. To unravel the nature of fragility, particularly in the light of the relationship between fragility and the inherent structural signature, we point out the role of the medium range order (MRO) and the boson peak (BP) in liquids and glasses. Here the MRO is defined by the decay of the pair distribution function with distance and the boson peak is expressed by the excess vibrational density of states over the Debye level due to local modes. We found that strong correlation exists among fragility, the MRO, and the BP. These observations could elucidate the mechanism that controls fragility and provide a guide for designing the glasses.
10:00 AM
Non-destructive Probing of Internal Damage Processes in a Metallic Glass: Amlan Das1; Robert Maass2; 1University of Illinois; 2Federal Institute for Materials Research and Testing
Metallic Glasses (MGs) deform via a shear localization in the inhomogeneous serrated plastic regime. This shear localization occurs repeatedly and post-mortem analysis of strained but intact samples has shown that shear-band cavities of substantial size emerge on the shear plane. It remains unclear when these cavities form along the serrated stress-strain curve, but it is of fundamental importance for the determination of correct flow stresses. In order to trace shear-band cavity-formation as a function of strain, we conduct in-situ acoustic emission experiments coupled with high-energy x-ray tomography. This approach is based on the hypothesis that spectral and energy component of the emitted elastic waves during internal damage accumulation allow the discrimination between shear-band formation and cavity formation. The tomography data is used to scrutinize the finding obtained via the acoustic emission approach.