Bulk Metallic Glasses XIX: Mechanical and Physical Properties II
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 8:00 AM
March 1, 2022
Room: 253C
Location: Anaheim Convention Center

Session Chair: Sezer Ozerinc, University of Illinois at Urbana-Champaign

8:00 AM  Cancelled
Elasticity and Configurational Thermodynamics of Metallic Glass Forming Liquids: William Johnson¹; Qi An²; ¹California Institute of Technology; ²Univ. of Nevada Reno
    The glass transition is characterized by configurational freezing of an undercooled liquid to a solid without crystallization. Glassy solids exhibit shear rigidity and therefore support long range elastic fields that alter the nature localized configurational excitations (STZ's, strings, etc.) as described by Eshelby in his classical treatment of elastic inclusions. This leads naturally to long range power law interactions between these local excitations that modify the configurational entropy of the liquid leading to a thermodynamic phase transition, or L-G transition. This problem is discussed in the context of recent MD simulations and experimental observations on metallic glass forming liquids.

8:25 AM
Assessment of Excess Entropy in Extremely Fragile Glasses: Hillary Smith¹; Claire Saunders²; Camille Bernal²; Stefan Haegeli Lohaus²; Marios Demetriou³; Brent Fultz²; ¹Swarthmore College; ²Caltech; ³Glassimetal
    A new series of ultra-fragile bulk metallic glasses (BMGs) Pt_80-xCu_xCu₂₀ were recently reported with Angell fragility parameters ranging from 73 to more than 90. The structure of these ultra-fragile BMGs was observed to collapse discontinuously at the glass transition, resembling a first order melting transition [1]. We report measurements of the excess entropy for two compositions, x=57 and x=60 with Angell fragilities of 73 and 82 for respectively. Inelastic neutron scattering measurements were performed while heating through the glass transition and crystallization. The difference in vibrational entropy between the glass/liquid and crystal is approximately 0.05kB per atom. The change in phonon spectrum across the glass transition was even smaller. This work is discussed in the context of our previous report on of the vibrational entropy through the glass transition in Cu₅₀Zr₅₀ and Cu₄₆Zr₄₆Al₈. [1] Na, J.H., et al., P.N.A.S. 117, 2779 (2020).

8:45 AM
Cu-Nb Metallic Glasses with High Hardness: Mohammad Abboud¹; Amir Motallebzadeh²; Özgür Duygulu³; Robert Maaß⁴; Sezer Ozerinc¹; ¹Middle East Technical University; ²Koç University Surface Science and Technology Center; ³TÜBİTAK Marmara Research Center Materials Institute; ⁴Federal Institute of Materials Research and Testing (BAM)
    We report on the mechanical properties of the Cu-Nb system over a wide compositional range of 31 – 83 at.% Cu. Characterization of the magnetron-sputtered thin films revealed a fully amorphous structure for Cu concentrations in the range of ~31–65 at.%. Nanoindentation measurements showed that hardness is about 7 GPa for Cu-rich samples and reaches 9 GPa as Cu concentration is reduced. The high hardness is considerably beyond the prediction by a rule-of-mixture that applies well to similar Cu-refractory metal binary glasses. For Cu concentrations of 70 at.% and higher, the microstructure evolves into a dispersion of Cu crystallites in the amorphous matrix. This regime exhibits a virtually constant hardness of about 7 GPa up to 83 at.% Cu. The findings provide insight into the structure-property relationships in Cu-Nb and highlight the vast design space to develop binary metallic glasses composed of immiscible metals.

9:05 AM
Observation of the Invar Effect by In-situ X-ray Diffraction in Fe-based Bulk Metallic Glasses: Alexander Firlus¹; Mihai Stoica¹; Stefan Michalik²; Robin Schäublin¹; Jörg Löffler¹; ¹ETH Zurich; ²Diamond Light Source
     An anomalously low coefficient of thermal expansion that suddenly increases around the Curie temperature is universally observed in ferromagnetic Fe-based bulk metallic glasses (BMGs). This effect is known as Invar effect and is rare to find in crystalline alloys. While many studies have shown the Invar effect exists in Fe-based BMGs at the macroscopic scale, there is little understanding on how the Invar effect manifests at the atomic scale of amorphous materials.In this work we studied the Invar effect of quaternary BMGs by in-situ high-energy X-ray diffraction. All diffraction halos contract with increasing temperature and show a transition in the contraction rate around the Curie temperature. Combining atomic-scale information with macroscopic dilatometry and magnetometry, we improve on the understanding of the Invar effect in amorphous materials.

9:25 AM Discussion on mechanical and physical properties of metallic glasses