Bulk Metallic Glasses XVII: Structures and Mechanical Properties
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 2:00 PM
February 26, 2020
Room: Cardiff
Location: Marriott Marquis Hotel
Session Chair: Jurgen Eckert, Erich Schmid Institute of Materials Science; Ramamurty Upadrasta, Nanyang Technological University
2:00 PM Invited
Relaxation Phenomena in Severely Deformed Bulk Metallic Glasses: Jurgen Eckert1; 1Erich Schmid Institute of Materials Science; Montanuniversität Leoben
The atomistic mechanisms underlying aging and rejuvenation of bulk metallic glasses (BMGs) are still unclear. Recent results indicate that structural relaxations on the nanometer scale and their percolation may be involved in the formation of shear transformation zones (STZs) and shear bands controlling the ductility. Hence, there is fundamental interest to understand the interplay of structural and dynamic relaxations for equilibrated as well as non-equilibrated BMGs for improving their ductility. For this, in-situ X-ray diffraction was used to study the structural rearrangements during annealing of CuZr-based BMGs driven out of equilibrium by severe plastic deformation. The structural changes are correlated with dynamic mechanical analysis (DMA), dilatometry and differential scanning calorimetry to determine dynamic relaxations and crystallization. We find that structural rearrangements occur at the same temperatures as the dynamic gamma, beta and beta’ relaxations determined by DMA, and will discuss the impact of these findings for plasticity improvement.
2:20 PM Invited
A Quantitative Connection Between Shear Band Mediated Plasticity
and Fracture Initiation Toughness of Metallic Glasses: Ramamurty Upadrasta1; 1NTU
It is well known that shear band mediated plasticity ahead of crack tips imparts high fracture toughness of 'ductile' BMGs, quantitative connection between those two material properties is yet to be established. In this work, we show that the mode I fracture initiation toughness, KIc, can be related to the shear band number, Ni, around spherical indentation impressions as well as the shear band density in the notch tip plastic zone. This result confirms that it is indeed the notch tip plasticity that determines KIc of BMGs. Possible connections between Ni and Nn, ways of enhancing the latter so as to increase KIc, and the central role played by the relative density of MGs in determining both elastic, plastic, and fracture responses will be discussed.
2:40 PM Invited
Toward Tunable Superelastic Bulk Metallic Glass Composite: Wook Ha Ryu1; Hyun Seok Oh1; Ji Young Kim1; Eun Soo Park1; 1Seoul National University
The design of modern high-performance structural engineering materials is driven by optimizing combinations of mechanical properties for predictable failure in service. Although many bulk metallic glasses (BMGs) exhibit high strength and substantial fracture toughness, they lack ductility and fail in an apparently brittle manner in unconstrained loading geometries. To solve this problem, various concepts of developing composite microstructure with in-situ/ex-situ formed secondary precipitates have been actively studied. The selection of secondary phase is a key parameter in designing BMG matrix composites to overcome the brittleness and improve their mechanical properties. In the present study, we report BMG matrix composites with “superelastic” secondary phase. We will carefully discuss how to optimize their mechanical properties by controlling the morphology and fraction of the secondary precipitates and phase transformation behavior during deformation, which can significantly enhance their sustainability. This report will provide a novel strategy of composite design via manipulating self-healable secondary phase.
3:00 PM Invited
Stress Breaks Universal Aging Behavior in a Metallic Glass: Amlan Das1; Peter Derlet2; Chaoyang Liu1; Eric Dufresne3; Robert Maass1; 1University of Illinois at Urbana-Champaign; 2Paul Scherrer Institute; 3Argonne National Laboratory
Using thermal and thermo-mechanical processing of metallic glasses to change their structural state has a long history. Annealing below the glass transition temperature is known to relax the structure, leading to an increase in structural relaxation times with time (age). This aging process is ubiquitous and has been captured with an empirical but universal time-waiting time-temperature superposition principle. Here we focus on the structural dynamics occurring in response to a mechanical stress within the elastic regime. This is done via in-situ x-ray photon correlation spectroscopy (XPCS) of a prototypical Zr-based metallic glass. We find that stress breaks the universal thermally-activated aging response: relaxation times increase with stress, but significant structural intermittency is seen that leads to distinct non-monotonous structural dynamics. These features are ascribed to microplastic processes, leading to the conclusion that structural evolution under the bias of stress is fundamentally different than conventional thermally-activated relaxation.
3:20 PM Cancelled
Behaviors of Disordered Alloys Under Various Temperatures and Pressures: Jianzhong Jiang1; X.D. Wang1; Q.P. Cao1; D.Z. Zhang1; 1Zhejiang University
Phase transitions in materials are the subject of great interest. The polyamorphic transition induced by temperature and/or pressure, defined as a transition between two different disordered phases (without long range translation and orientation symmetries and with the same composition) in disordered materials, e.g., liquids and amorphous materials, is often more complex as compared to the polymorphic transition in crystalline materials. In this talk, we will survey behaviors of disordered alloys (metallic liquids and metallic glasses) under various temperatures and pressures. Firstly, temperature-dependent atomic structure evolutions in various metallic liquids (from pure element to multi-component systems) will be mentioned, esp. challenges and potential for liquid-to-liquid transition in metallic liquids will be critically discussed. Secondly, pressure-induced phase transformation in various metallic glasses will be further discussed. Finally, simultaneously temperature- and pressure-induced polyamorphic transitions in one metallic system will be presented.
3:40 PM Break
4:00 PM Invited
Small-scale Mechanical Behavior of Metallic Glasses and their Composites: Shristy Jha1; Nandita Ghodki1; Vahid Hasannaeimi1; Maryam Sadeghilaridjani1; 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.
4:20 PM
Evolution of Material Properties in Fragile Bulk Metallic Glasses: Sydney Corona1; Jong Hyun Na2; William Johnson1; 1California Institute of Technology; 2Glassimetal Technology
Many material properties of bulk metallic glasses (BMGs) have been investigated (e.g. strength, toughness, etc.). However, limits of the glass forming ability have left the fragile regime of BMGs predominantly unexplored. Utilizing a high Angell fragility platinum-based glass with m tunable from 60 to 90+, various trends and properties are observed. In this study, high fragility influences configurational enthalpies of the glass transition, in-situ shear and ex-situ shear, Bulk, and Young’s moduli, and internal stress profiles. These results reveal first-order behavior in the glass transition in the high fragility limit. The elastic moduli support this interpretation and the internal stress profiles provide insight into the underlying mechanism. Further, these results add to and improve the understanding of BMGs and their material properties (e.g. strength, toughness, etc.).
4:40 PM Invited
Anelastic Relaxation as a Probe of Structural Evolution of Metallic Glasses: Michael Atzmon1; Tianjiao Lei1; 1University of Michigan
Using a combination of measurement methods, we have observed anelastic relaxation of metallic glasses over ten orders of magnitude of time. Reliable relaxation-time spectra could be computed from the data. These exhibit distinct peaks, which are consistent with an atomically-quantized hierarchy of shear transformation zones (STZs). The methodology we developed allows for detailed characterization of the effect of structural evolution. In La-based alloys, room-temperature ageing decreases the number of the slowest potential shear transformation zones, associated with the main (alpha) relaxation. It also increases their corresponding time constants, which is a result of the increasing shear modulus. Cryogenic cycling reverses the effect of ageing on the time constants, but not that on the number of potential STZs. While the secondary (beta) relaxation is also consistent with the STZ model and is part of the atomically-quantized hierarchy of STZs, it is not affected by room-temperature ageing for the durations probed.
5:00 PM Invited
Structural Modifications and their Effect on the Mechanical Properties of a Zr-based Metallic Glass: Bernd Gludovatz1; Lisa Krämer2; Bosong Li1; Amir Monfared1; Keita Nomoto3; Anna Ceguerra3; Christoph Gammer4; Anton Hohenwarter2; Simon Ringer3; Jürgen Eckert4; Jamie Kruzic1; 1UNSW Sydney; 2University of Leoben; 3The University of Sydney; 4ESI-Leoben
The excellent combination of properties like high strength, low stiffness, and large elastic strain limits make bulk-metallic glasses (BMGs) candidate materials for many structural applications. Major drawbacks for their use in engineering fields are highly variable fracture toughness values and limited ductilities. Here, we will show how precise heat-treatments and structural modifications through high-pressure torsion (HPT) can be used to specifically tailor the microstructure of the glass Zr52.5Cu17.9Ni14.6Al10Ti5 (Vitreloy 105). Using maps of small load Vickers hardness indents we identify soft and hard regions in the glass and correlate their distribution with the material’s stress-strain behavior in tension. We furthermore identify clearly distinguishable failure characteristics in fracture toughness tests using the as-cast, annealed and HPT-deformed samples. Our results clearly indicate the potential of thermo-mechanical processing to alter the mechanical properties of metallic glasses and provide a pathway to improved damage tolerance in these materials.
5:20 PM Cancelled
Microstructural Optimization and Tensile Properties of Ti-based Bulk Metallic Glass Composites Containing Metastable β-Ti: Long Zhang1; Haifeng Zhang1; 1Institute of Metal Research, Chinese Academy of Sciences
In this talk, the effects of dendrite sizes, phase stability and volume fractions of metastable β-Ti on tensile behavior of Ti-based BMGCs will be introduced. Results show that BMGCs containing larger size of metastable β-Ti are prone to deformation-induced transformation and exhibit larger tensile plasticity. If β-Ti is very stable during deformation, BMGCs show work-softening dominated plasticity; if β-Ti is metastable, BMGCs exhibit small tensile plasticity with pronounced serrations arising from strain localization in both phases; and if β-Ti is unstable sufficiently for deformation-induced transformation, BMGCs show large work-hardening dominated plasticity. The yield strength of BMGCs is correlated with the phase stability of metastable β-Ti. With increasing the volume fraction of β-Ti in BMGCs, the yield strength decreases but the tensile plasticity as well as work-hardening capability increase. Based on these understandings, a large-sized BMGC with optimized microstructure has been developed which exhibits a good combination of properties.