Bulk Metallic Glasses XX: Fracture and Deformation
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, The Chinese Academy of Sciences; Lindsay Greer, University of Cambridge; Peter Liaw, University of Tennessee

Thursday 2:00 PM
March 23, 2023
Room: Aqua C
Location: Hilton

Session Chair: Daniel Sopu, Erich Schmid Institute


2:00 PM  Invited
Are Metallic Glasses Brittle or Ductile?: Jan Schroers1; 1Yale University
     Crystalline metals generally exhibit ductility which is enabled by dislocation sliding. We show here that metallic glasses, which carry ductility through shear banding as opposed to dislocation sliding, exhibit ductility only in certain stress fields and such ability is an intrinsic property. Such ability, only depending on chemistry and fictive temperature of the metallic glass, manifests in the ability to form stable shear bands that carry plasticity. We measured this quantity, for a range of metallic glasses to represent the material class of metallic glasses. If a metallic glass behaves ductile or brittle in a given application is determined by the comparison between and the applied stress field, ; if > the metallic glass will behaves brittle, if < the metallic glass will behaves ductile, and indicates how ductile. Measured , and the concept of comparing it with can explain the mechanical properties of metallic glasses and their apparent contradicting brittle and ductile characteristics. Proposed concept allows to determine the behavior of a metallic glass in an application and lays the foundation of using metallic glasses as structural materials.

2:20 PM  Invited
Fracture Toughness of Bulk Metallic Glass Composites: Ramamurty Upadrasta1; Devashish Rajpoot2; Parag Tandaiya2; R Lakshmi Narayan2; Long Zhang3; 1Nanyang Technological University; 2IIT-Bombay; 3Institute of Metal Research
    Toughness of bulk metallic glass matrix composites (BMGCs) with both transforming and non-transforming β-Ti dendrites in different loading modes and at different temperatures was examined. In all cases, mode II toughness is considerably lower than in mode I, while stable crack growth in mode I is insignificant whereas it is considerable in mode II. The toughness of BMGCs reinforced with coarse but non-transforming dendrites in both the modes is higher than the respective values in BMGCs with transforming β-Ti despite their ability to strain harden. The fracture criterion and mechanism of BMGCs is identical to that in BMGs. was found to be brittle when cast in a large size. Additionally, results of the experiments conducted to investigate the embrittlement of a β-Ti dendrite reinforced Zr-based BMGC and the effectiveness of the cryothermal cycling treatment in restoring the mode I toughness will be presented.

2:40 PM  
Medium-range Order Controls Hardness and Fracture Toughness in Bulk Metallic Glasses: Jamie Kruzic1; Keita Nomoto2; Bosong Li1; Christoph Gammer3; Anna Ceguerra2; Huma Bilal2; Anton Hohenwarter4; Jürgen Eckert4; Bernd Gludovatz1; Simon Ringer2; 1University of New South Wales (UNSW Sydney); 2University of Sydney; 3Austrian Academy of Sciences; 4University of Leoben
    Bulk metallic glasses (BMGs) can range from tough to brittle depending on their structural state; however, quantifying their structure-property relationships has been an unresolved challenge. We overcame this challenge by utilizing nanobeam electron diffraction and fluctuation electron microscopy to develop structure-property relationships for three different Zr-based BMG compositions, two different manufacturing routes (cast and laser powder bed fusion), and various thermo-mechanical histories (cryogenically-cycled, cold deformed, etc.). Our findings revealed that local hardness within the BMG microstructure is controlled by the size and volume fraction of FCC-like medium-range order (MRO) clusters. We have proposed a model of ductile phase softening whereby relatively soft FCC-like MRO clusters sit in a matrix of harder icosahedral dominated ordering. Furthermore, the relationships between hardness and MRO for the various BMGs are maintained after different relaxation and rejuvenation treatments where hardening and softening can be correlated with embrittlement or toughening of the macroscopic BMG properties, respectively.

3:00 PM  
Effect of Annealing and Cryogenic Treatment on the Size-dependent Deformation Behavior of the Metallic Glass: Akib Jabed1; Golden Kumar1; 1UT-Dallas
    Size-effects in deformation behavior of metallic glasses (MGs) have attracted growing interest due to their potential to improving the plasticity. It has been observed that sub-micron sized MGs exhibit homogeneous-like deformation and can accommodate more plastic strain. The mechanism of size-effects in MGs remains controversial because of sample preparation artifacts and limited size range of test specimens. Here, we report fracture behavior of a wide range of MG specimens fabricated by irradiation free thermoplastic drawing. The samples with diameters ranging from 100 nm to 10 µm are tested are tested. The role of structural state on the size-effects is investigated by testing the samples in the as-cast state and after thermal and cryogenic treatments. The effects of sample size and structural state on the fracture morphology and plasticity of MGs are studied. The results are combined to present a unified model for size-effects in deformation behavior of MGs.

3:20 PM  Invited
An Atomic-level Perspective of Shear Banding in Metallic Glasses: Daniel Sopu1; Jürgen Eckert1; 1Erich Schmid Institute of Materials Science of the Austrian Academy of Sciences
    Over the last decades considerable efforts have been done to better understand the mechanisms controlling shear banding in metallic glasses. Atomistic simulations highlight the importance of nanoscale stresses and strains heterogeneity, but corresponding experimental proofs are scarce due to limited characterization techniques. Here, by means of MD and athermal quasi-static simulations we derive an atomistic description of the relationship between the deformation behavior of metallic glasses and their intrinsic properties. The shear band characteristics are evaluated using the two-unit STZ-vortex mechanism. A series of fundamental insights into shear band formation, shear band branching and multiplication or the transition from shear banding to cracking are revealed. Some of these results are, for the first time, corroborated by experimental observations performed at the nanoscale level and obtained by using precession nanodiffraction mapping in the transmission electron microscope.

3:40 PM Break

4:00 PM  Invited
Observation of Deformation Features in Metallic Glasses: Sangjun Kang1; Xiaoke Mu1; Di Wang1; Arnaud Caron2; Christian Minnert3; Karsten Durst3; Christian Kuebel1; 1Karlsruhe Institute of Technology; 2Korea University of Technology and Education; 3TU Darmstadt
     The application of metallic glasses is limited by their lack of toughness and catastrophic failure during plastic deformation. However, the underlying shear banding mechanisms are still not fully established and understanding the structure of shear bands, their formation and interaction is essential to establish a general theory of the nature of glasses and their mechanical deformation. We have developed a 4-dimensional scanning transmission electron microscopy (4D-STEM) technique to not only map nanoscale pair distribution function (PDF) variations, but further investigate strain and packing/density variations at the nanoscale in deformed metallic glasses. Using this new approach, we discovered Eshelby-like quadrupolar strain fields percolated along shear bands and their correlation with packing/density variations on the shear bands. These results provide direct experimental data about the deformation structures in metallic glasses and help to understand the differences between brittle and more ductile glasses.

4:20 PM  
Steady-state Serrated Flow Induced by Rejuvenation Gradient in Zr-based Bulk Metallic Glass: Wook Ha Ryu1; Won-Seok Ko2; Rui Yamada3; Geun Hee Yoo1; Junji Saida3; Eun Soo Park1; 1RIAM, Seoul National University; 2Inha University; 3Tohoku University
    In this work, we propose novel methods to utilize the rejuvenation phenomenon to heterogeneously modulate local energy states and free volume (FV) content in bulk metallic glasses (BMGs). We induce rejuvenation gradient in BMG through deep cryogenic treatment using LN2. The gradient structure prevented strain softening and induced apparent hardening to maintain steady-state serrated flow during compressive plastic deformation. The major and minor shear bands intersect at the gradient interface, which prevents softening in the shear plane by interfering with the propagation of the major shear plane. The plastic strain increased significantly due to the stable steady-state serrated flow. Key factors in improving mechanical properties are the change in critical shear stress and shear band angle in the local area of BMG according to the FV gradient. The post-processing methods in this study are simple, non-destructive, and can dramatically improve the mechanical properties of BMGs.

4:40 PM  
Structure-Dynamics Relationships in Cryogenically Deformed Bulk Metallic Glass: Jurgen Eckert1; Florian Spieckermann2; Baran Sarac1; Daniel Sopu1; 1Erich Schmid Institute of Materials Science; 2Montanuniversitaet Leoben
    The atomistic mechanisms governing aging and rejuvenation in glasses are still unclear. In-situ X-ray diffraction allows to investigate the structural rearrangements during annealing from 77 K up to crystallization in Cu-Zr-Al-Hf-Co bulk metallic glass, rejuvenated by high pressure torsion at cryogenic and room temperature. The configurational entropy calculated from X-ray pair correlation functions gives a structural footprint of deformation-induced rejuvenation. With synchrotron radiation, temperature and time resolutions comparable to calorimetry are possible, allowing to correlate changes in atomic configuration to calorimetric signals and to attribute those to changes of dynamic and vibrational α-, β- and γ-relaxations. The results suggest that the structural footprint of the β-transition is related to entropic relaxation with first-order characteristics. Dynamic mechanical analysis reveals that non-reversible structural rearrangements are preferentially activated throughout the β-transition. The low-temperature γ-transition mostly triggers reversible deformations with a change of slope in the entropic footprint suggesting second-order characteristics.