Bulk Metallic Glasses XIX: Homogeneous and Inhomogeneous Deformation & Mechanical and Physical Properties I
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

Monday 2:00 PM
February 28, 2022
Room: 253C
Location: Anaheim Convention Center

Session Chair: Katharine Flores, Washington University in St. Louis

2:00 PM  Invited
Unveiling the Local Atomic Arrangements and Short-circuit Diffusion in Shear Bands: Reda Chellali1; Sree Nandam1; Horst Hahn1; 1Karlsruhe Institute of Technology (KIT)
    It is proposed to use the atom probe tomography characterization to achieving a detailed knowledge on the chemical and the structural variation in Shear bands and compare these results with the parent bulk metallic glass. This is achieved by analyzing the density fluctuation and short-to-medium-range order in selected systems. Atomic transport along the shear band is also measured. The significant, by orders of magnitude, enhancement of the diffusion rate with respect to that in the surrounding matrix suggests that the shear bands represent short-circuit diffusion paths. Our findings will provide a reliable chemical/structural study, which may help us to understand the nature, and properties of metallic glasses.

2:25 PM  
Small-scale Deformation Behavior of Metallic Glasses and Their Composites: Nandita Ghodki1; Shristy Jha1; Saideep Muskeri1; Sundeep Mukherjee1; 1University of North Texas
    Small scale mechanical behavior of several metallic glasses and their composites were evaluated for fundamental understanding of mechanical response at microstructural length-scales including micro/nano-pillar compression, fatigue, creep and fracture toughness. The creep response was evaluated as a function of loading rate and peak load and will be discussed in the context of shear transformation zones. Strain rate sensitivity was evaluated by micro/nano-pillar compression at different strain rates. Metallic glass composites have a unique microstructure consisting of crystalline dendrites in an amorphous matrix, which leads to distinct crack deflection mechanisms. Site-specific deformation behavior of some of these alloys was studied and phase-specific stress-strain response was evaluated for mechanistic understanding of the bulk response and toughening in these alloys.

2:45 PM  
Strength, Ductility and Elasticity of Metallic Glass Nanoparticles and Bulk Nano-glasses: Wendy Gu1; Melody Wang1; Mehrdad Kiani1; Abhinav Parakh1; Anabelle Colmenares1; 1Stanford University
    Colloidal synthesis is a solution-based pathway for fabricating metal-metalloid metallic glass nanoparticles, which can then be consolidated into nanostructured, bulk metallic glasses. The particles form through a cluster-mediated growth process which results in heterogeneous density. Here, we compare the mechanical behavior of iron-boron and nickel-boron particles tested using in-situ SEM and TEM mechanical testing. The high ductility of these particles is related to their size and atomistic structure. High pressure diamond anvil cell and synchrotron X-ray measurements are used to determine bulk modulus and compressibility under hydrostatic pressure. Nanostructured, bulk metallic glasses are formed from the iron-boride particles. These nano-glasses consist of amorphous grains connected by amorphous regions of lower density. The role of the amorphous interfaces is revealed through nanoindentation and micropillar compressions.

3:05 PM  
On the True Stress-strain Curve of Metallic Glasses: Amlan Das1; Catherine Ott1; Dinesh Pechimuthu2; Robabeh Moosavi2; Anja Waske2; Mihai Stoica3; Robert Maass2; 1University of Illinois Urbana Champaign; 2Federal Institute of Materials Research and Testing; 3ETH Zurich
    Testing nominally identical bulk metallic glass (BMG) samples yields a large variety of post yielding behavior of which the fundamental origin remains unclear. This stands in stark contrast to the robust pre-yield behavior and a high Weibull modulus of the yield stress. Several studies have revealed that non-negligible internal micro-cracking (shear-band cavities) occurs in the inhomogeneous deformation regime (Acta Materialia 140 (2017) 206; Scripta Materialia 170 (2019) 29). To shed light onto the true-stress strain behavior, the strain-dependent evolution of internal damage is assessed along a full flow curve. We present a combined acoustic-emission and x-ray tomography study that tracks the internal shear-band cavity-growth as a function of strain, giving access to a true stress-strain curve. This data reveals an exponential growth of internal shear-band cavities with strain and a fractal cavity morphology. This unpredictable cavity growth process explains the large variability of post-yield behavior seen in the literature.

3:25 PM Break

3:40 PM  
A Cavity-based Micromechanical Model for the Shear Band Failure in Metallic Glasses under Arbitrary Stress State: Yanfei Gao1; 1University of Tennessee-Knoxville
    A mechanistic model for the failure analysis in metallic glasses requires the knowledge of the entire deformation and damage evolution processes, in contrast to the overly simplified critical free volume or strain model. Motivated by the intergranular cavity-controlled fracture in polycrystals, here we propose that metallic glass failure is governed by the cavity growth inside the shear band under the concomitant processes of diffusive process inside and creep deformation outside the shear band. The competition between diffusion and creep leads to a length scale. When the hydrostatic stress is large, the cavity growth is found to be dominated by diffusional processes, and the above-mentioned length scale becomes the Stokes-Einstein type. When the stress state is predominantly shear, small deformation analysis will not exhibit cavity growth; it is the large shear distortion and cavity coalescence that gives the final failure. A failure map is constructed with respect to arbitrary stress states.

4:00 PM  
Measuring Metallic Glass Viscosities over Wide Composition Ranges: Sebastian Kube1; Sungwoo Sohn1; Theo Evers1; Will Polsky1; Rodrigo Ojeda-Mota1; Kevin Ryan1; Sean Rinehart1; Yong Sun1; Jan Schroers1; 1Yale University
    Amongst the most fundamental properties of metallic glass (MG) forming liquids are the viscosity and its temperature dependence, the fragility. Measuring these is challenging and data have only been reported for few compositions and systems. Here, we present a new experimental method to measure the viscosity and fragility across wide composition ranges: Using co-sputtering and silicon etching, we prepare compositionally graded wafers, which are then cleaved out into individual chips with freely suspended circular MG thin film membranes. Applying gas pressure, these membranes are thermoplastically deformed between Tg and Tx. As the membranes expand into spherical shape, we track the deformation rate as function of the temperature and pressure difference, from which we compute viscosities for the full temperature range. We map out and discuss the fragility behavior for ~200 compositions in the Mg-Cu-Y system with elemental concentrations ranging over 20 at.%.

4:20 PM  
Shear Fracture in Bulk Metallic Glass Composites: Devashish Rajpoot1; R.L. Narayan1; Long Zhang2; Parag Tandaiya1; Ramamurty Upadrasta3; Punit Kumar4; 1IIT-Bombay; 2Institute for Metals Research, CAS; 3Nanyang Technological University; 4LBNL
    Fracture behavior of bulk metallic glass matrix composites (BMGCs) with both transforming and non-transforming β-Ti dendrites under shear and opening modes was examined. Experimental results show that the fracture toughness of all three BMGCs is considerably lower in mode II than in mode I. However, 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. Fracture surface features and shear band patterns at notch tips indicate that the fracture criterion and mechanism of BMGCs is identical to that in BMGs. Implications of these results in terms improving the fracture toughness of BMGCs with transforming dendrites will be discussed.

4:40 PM Discussion on deformation of metallic glasses