Bulk Metallic Glasses XIX: On-Demand Oral Presentations
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 8:00 AM
March 14, 2022
Room: Advanced Materials
Location: On-Demand Room
Are Metallic Glasses Brittle or Ductile?: Jan Schroers1; 1Yale University
Ductility is an important characteristic of crystalline metals as it is associated with high fracture toughness. The plastic strain occurring under tensile loading is a quantitative measure of ductility. Metallic glasses (MGs) generally lack global ductility. However, they can exhibit remarkable high fracture toughness. MGs also exhibit ductility when loaded in bending as long as the sample is thin, less than ~10 times its plastic zone size. We discuss this apparent discrepancy and introduce a critical stress gradient which is required for metallic glasses to exhibit plasticity. We will then discuss the characteristics of MGs which indicate a high tendency for plasticity. Here, we distinguish between the contribution from chemical composition and processing, where the latter is often quantified in the fictive temperature.We will then attempt to correlate the metallic glasses’ ability to plastically deform with its structure.
Atomic Motion in Ultrastable Metallic Glasses: Beatrice Ruta1; Martin Luettich2; Konrad Samwer3; 1Univ Lyon 1 and CNRS; 2ESRF and Goettingen University; 3Goettingen University
A major obstacle in the use of glasses is their instability over time due to ongoing relaxation processes. This is particularly the case for metallic glasses where aging can lead even to fractures or crystallization. Ultrastable MGs keep the promise to overcome this problem. As suggested by their name, they are claimed to be stable with respect to their previous thermal history and physical aging, which makes of them ideal materials for technological applications. Thanks to the use of intense coherent X-rays, we have investigated the collective atomic motion in ultrastable MGs. We find a signature of ultrastability at the atomic level that results in a slower relaxation dynamics with respect to that of conventional Mgs, and in a peculiar acceleration of the dynamics close to the glass transition . This surprising phenomenon can be understood in the framework of the potential energy landscape.
Relaxation Dynamics in Glass Forming Alloys: Microscopic Nature, Timescales and Aging Effects: Eloi Pineda1; 1Universitat Politècnica de Catalunya
The atomic mobility in the glass transition region involves timescales going from milliseconds to hours. The description of the atomic dynamics in this temperature region is complex due to the change from the ergodic liquid to the out of equilibrium glass, the inherent coincidence of experimental and material timescales and the presence of both diffusion and stress-driven atomic rearrangements. In addition, the timescales are far from being accessible by simulation. Small stress and strain mechanical relaxation experiments and X-ray photon correlation spectroscopy are unique techniques to directly probe the atomic mobility of metallic glass forming systems. This work will present recent experiments that unveil the nature, temperature behavior and aging dependence of the various mechanisms that contribute to the atomic movement in metallic glasses, which comprise: 1) drift-like movement due to free volume release; 2) athermal, stress-driven, anelastic relaxation; and 3) thermally activated, diffusion-like atomic mobility.
Shear Bands in Metallic Glasses: Local Structure, Atomic Mobility and Relaxation Kinetics: Gerhard Wilde1; 1University Of Muenster
Exceeding the elastic limit during deformation of metallic glasses causes shear localization and work softening. Microscopically, it is the local atomic structure and its intrinsic heterogeneity that governs atomic mobility as well as the relaxation behavior of glasses. Yet, the structure and properties of the shear bands are often not considered in detail and assumed to be similar to the original glass. We have performed a comprehensive study concerning the local medium range order structures inside and outside shear bands before and after plastic deformation. Additionally, the strain fields adjacent to shear bands and the MRO of shear-affected zones have been determined. For identical deformation states, the self-diffusivity has been determined after the shear has ceased. The results of these complementing analyses are discussed with respect to the description of inhomogeneous plastic flow of metallic glasses.
STZ-vortex Unit – The Key to Understand and Control Shear Banding in Metallic Glasses: Daniel Sopu1; Xudong Yuan1; Jürgen Eckert1; 1Erich Schmid Institute of Materials Science of the Austrian Academy of Sciences
The ability to control plastic deformation of MGs is based on the capacity to influence the activation and percolation of shear transformation zones (STZs) that ultimately leads to shear band formation. Here, by calculating the atomic strain and simultaneously occurring directional rotation fields, a novel and more complete perspective of STZ activation is proposed, highlighting its Eshelby-like inclusion characteristics. The novel STZ-vortex mechanism provides an atomistic description of deformation mechanisms like shear band formation and propagation, shear band branching and multiplication or shear band blocking and deflection. Additionally, STZ-vortex mechanism has of primary importance for understanding the brittle-to-ductile transition from cracking to localized shear banding and homogeneous deformation. Through the proper control of the STZ-vortex sequence, one could handle the shear band dynamics and avoid runaway instability, thereby improving the plastic deformability of metallic glasses at room temperature.
Size-dependent Freezing Kinetics of Bulk Metallic Glasses: Isabella Gallino1; Daniele Cangialosi2; Sascha Riegler1; Golden Kumar3; 1Saarland University; 2Donostia International Physics Center; 3The University of Texas at Dallas
Fast scanning calorimetry (FSC) has recently emerged as a novel technique for studying the freezing process in glass forming liquids in an unprecedentedly large range of cooling rates and frequency. For bulk metallic glass-forming alloys, FSC-investigations have demonstrated that the atomic dynamics in the deeply undercooled liquid are heterogeneous and involve relaxation processes that are faster than the structural α-relaxation, reflecting their multicomponent nature [1]. Here, we report upon an attempt to reduce gradually the length scale of the sample confinement to study the shift of the glass transition temperature (Tg) during vitrification to lower temperatures, i.e., a more pronounced Tg-reduction with respect to that observed in the bulk material. The results are compared to the α-relaxation process, which remains size independent.[1] X. Monnier, D. Cangialosi, B. Ruta, R. Busch, I. Gallino, Vitrification decoupling from α-relaxation in a metallic glass. Sci. Adv.6, eaay1454 (2020). DOI: 10.1126/sciadv.aay1454
Strength-controlled Fracture of Metallic Glass at the Micrometer Scale: Ruitao Qu1; Robert Maaß2; Zengqian Liu3; Robert Ritchie4; Zhefeng Zhang3; Cynthia Volkert5; Feng Liu1; 1Northwestern Polytechnical University; 2University of Illinois at Urbana-Champaign; 3Institute of Metal Research, Chinese Academy of Sciences; 4Materials Sciences Division, Lawrence Berkeley National Laboratory; 5Institute of Materials Physics, University of Göttingen
Smaller metallic glass (MG) samples usually exhibit higher plasticity accompanying with more ductile fracture behavior. Here we show micro-fracture testing results using a brittle Co-based MG and a ductile Zr-based MG. Surprisingly, higher toughness values were measured in larger rather than smaller samples for both MGs. Comparing the two different MGs, unexpectedly, higher toughness values were measured in the macroscopically more brittle Co-based MG than the Zr-based MG. Besides, the fracture stress of microscale crack-contained Co-based MG sample does not drop with increasing crack size or size of self-similar samples, showing a flaw insensitive behavior in brittle MG at the micrometer scale. These interesting results of MG failure at small length scale can be attributed to a transition of controlling factor for fracture from toughness in macroscale to strength in microscale.
Systematic Identification of Local Shear Events during the Plastic Deformation of Colloidal Glasses: Frans Spaepen1; 1Harvard University
The plastic deformation of metallic glasses is governed by the irreversible shear of subsets of the system (shear transformation zones; STZs). Each STZ is surrounded by a characteristic elastic strain field, first described by Eshelby. Although the Eshelby strain field is readily observable in two-dimensions, it has been observed only sporadically in three-dimensional systems. Colloidal glasses, in which particles are tracked by confocal microscopy during shear deformation, allow systematic exploration of the occurrence and evolution of Eshelby-type shear events in large experimental systems. Cross-correlation of the three-dimensional Eshelby strain field with the strains that develop during deformation reveals STZ spectra that evolve over the course of the deformation. The corresponding constitutive law can be tested against the macroscopic shear. The stress-strain relation can be measured both macroscopically, by coupling the glass to a calibrated elastic gel, and microscopically from the local structural misanthropy.
Shear Band Interactions in Bulk Metallic Glass Composites: Jurgen Eckert1; 1Erich Schmid Institute of Materials Science
The improved deformation behavior of bulk metallic glass composites (BMGCs) compared to monolithic glasses render these materials interesting for possible applications. However, the details of the deformation mechanisms are still not fully clear. Here, we report on BMGCs containing metastable β-Ti dendrites, crystals with dislocation-mediated plasticity or shape memory crystals, revealing that the overall deformation behavior can be significantly altered by the deformation characteristics of the crystals and/or by cooperative shear events of shear bands in the glassy matrix and strain-induced ω-Ti bands in β-Ti dendrites. If the crystals deform via dislocations, SBs are narrow and getting mature. In comparison, SBs in shape memory BMGCs continuously broaden by following thick martensitic plates without maturing, and broad SBs bifurcate, inducing formation of more martensitic variants and promoting strain delocalization. The broadening and bifurcation cause SB blunting, accounting for the superior plasticity and work-hardening capability of shape memory MGCs.
Cancelled
Relative Contributions of Local Structural State, Elastic Perturbation, and Heat Generation to Plasticity in Metallic Glass: Thomas Hardin1; 1Sandia National Laboratories
Plasticity in metallic glass can be conceptualized as a chain of discrete shear transformations (STs). Activation of a particular ST is modulated by local stress, temperature, and structural state. Each ST biases future STs by several mechanisms, including (1) modification of local structural state, (2) perturbation of the stress field via local plastic strain and elastic modulus modification, and (3) generation of heat via plastic dissipation. There remains some uncertainty around the interplay between and relative importance of these mechanisms in producing metallic glass plasticity. This talk presents an advanced mesoscale/kinetic Monte Carlo ST Zone Dynamics simulation method in which each of these mechanisms can be toggled, illuminating mechanism-effect relationships. This talk covers both the physical insight derived from these experiments and associated advances in the ST Zone Dynamics method.SNL is managed and operated by NTESS under DOE NNSA contract DE-NA0003525 (SAND2021-7433 A).
Nature of the Medium-range Order Distinct from
the Short-range Order in Metallic Liquids: Chae Woo Ryu1; Takeshi Egami1; 1University of Tennessee
Structure-property relations of metallic liquids and glasses are difficult to identify owing to the absence of long-ranged translational periodicity. To unravel a long-lasting conundrum, we study the pair distribution function (PDF) of metallic liquids determined by X-ray scattering experiments and molecular dynamics simulation. The first peak of the PDF describes the short-range order (SRO) in the nearest neighbor atoms, whereas the peaks beyond the first peak represent the medium-range order (MRO). The disparate natures of the SRO and MRO are clearly seen not only in their variations with temperature but also in the dynamic correlations of atoms. The result suggests that the MRO is distinct in nature from the SRO and plays a major role in the viscosity of supercooled liquids. Our analysis provides valuable insight into elucidating the structure and properties of metallic liquid.
Atomic Structure of Bulk Metallic Glasses/Liquids Studied by Synchrotron-radiation X-ray Diffraction, Scanning Tunneling Microscopy and Ab-initio Molecular Dynamics Simulation: Dmitri Louzguine1; 1WPI-AIMR, Tohoku University
Structural changes in a Zr-Cu-Ni-Al bulk glass-forming, relatively "strong", liquid alloy on cooling from above the equilibrium liquidus temperature studied by synchrotron radiation X-ray diffraction and first-principles molecular dynamics (MD) simulation are compared with those of a "fragile" Pd-Cu-Ni-P one. According to the results chemical ordering forming Zr-Cu,Ni, Zr-Al and Zr-Zr atomic pairs takes place in the Zr-Cu-Ni-Al supercooled liquid alloy on cooling. However, here the change in the Zr-Cu,Ni peak area to other peaks area ratio is smaller than in case of the Pd-Cu-Ni-P alloy (Cu,Ni-P to other peaks ratio) in accordance with a lower fragility index of the Zr-Cu-Ni-Al melt. It indicates that fragility is a sign of instability of short and medium range order in fragile liquids. The atomic structure of a Ni-Nb bulk metallic glass was studied by means of ultra high vacuum scanning tunneling microscopy. Direct atomic structure observation was supported by MD simulation.
Cryogenic Thermal Cycling of a Pd43Cu27Ni10P20 Bulk Metallic Glass: Miguel B. Costa1; Juan J. Londoño2; Andreas Blatter2; Michael Carpenter3; A. Lindsay Greer1; 1Department of Materials Science and Metallurgy, University of Cambridge; 2Research and Development Department, PX Services; 3Department of Earth Sciences, University of Cambridge
The Pd43Cu27Ni10P20 alloy is a prototypical bulk metallic glass (BMG) former: it possesses a wide supercooled liquid regime (ΔTx) and high resistance to crystallization, permitting casting and shaping under moderate conditions realisable in industrial practice. These factors, coupled with its intrinsic properties, make this Pd-based alloy attractive for practical applications (e.g. biomedical applications). However, this alloy is known to be relatively brittle in the as-cast state (i.e. limited plasticity near room temperature), limiting its use. The properties of a glass are dependent on its state, which, in turn, depends on the cooling rate from which it was formed. Once solidified, it is possible to thermomechanically treat MGs into a different energy state, both higher (‘rejuvenation’) and lower (‘relaxation’). In this work, we investigate the effects of cryogenic thermal cycling on Pd43Cu27Ni10P20 BMG samples, with special focus on the impact of the technique on mechanical properties.
New (Fe0.5Co0.5)71.64B19.104Si4.776Nb3.98Cu0.5 Bulk Glassy Alloy: A Comprehensive Time-resolved Synchrotron X-ray Study: Mihai Stoica1; Gavin Vaughan2; Jonathan Wright2; Jörg Löffler1; 1ETH Zurich; 2European Synchrotron Radiation Facility
Finemet and Vitroperm-type nanocrystalline alloys are very attractive for applications. Their particular nanostructure, consisting of (Fe,Si) grains embedded in a residual amorphous matrix, results from the thermal treatment of the metallic glass precursor. The magnetocrystalline anisotropy is averaged-out because of the very small dimension of the grains and their uniform distribution. This makes them extremely soft-magnetic, but mechanically quite fragile and brittle. Recently we demonstrated that by microalloying of Cu to a known bulk metallic glass-forming alloy one can obtain a similar structure in bulk form, which is more robust and reveals very good and tailorable soft-magnetic properties. The nanocrystallization process can be controlled over an interval of more than 100 K. Here we present a comprehensive study of this process by analyzing the reciprocal-space and direct-space data obtained from in-situ X-ray diffraction using high-energy, high-intensity synchrotron radiation.
Influence of Medium Range Ordering on the Deformation Behavior and Mechanical Properties of Metallic Glasses: Yuchi Wang1; Pengyang Zhao2; Soohyun Im1; Jinwoo Hwang1; Yunzhi Wang1; 1The Ohio State University; 2Shanghai Jiao Tong University
Medium range ordering (MRO) is an important nanoscale structural heterogeneity in metallic glasses (MGs) that has been observed experimentally and shown direct correlation with the mechanical properties. Using a heterogeneously randomized STZ model with direct input on MRO structures from experiments, we explore the relationship between MRO and shear band formation in MGs. Based on experimental characterization using 4-D STEM, different types, sizes, and spatial distributions of MRO domains are considered in the simulations. MRO having different symmetries are assumed to have different shear modes, activation energy barriers, transformation strains, and softening behaviors from each other and from the glassy matrix. The simulation results indicate that the “strain frustration” mechanism helps to explain the correlation between the MRO structure and ductility, while “hard” or “soft” MROs show different responses during deformation. This experimentally informed parametric study provides the MRO-properties relationship of MGs, shedding light on future design of ductile MGs.
Long-time Structural Evolution of a Metallic Glass at Elevated Temperature Measured by XPCS: Birte Riechers1; Amlan Das2; Eric Dufresne3; Robert Maass1; 1Federal Institute for Materials Research and Testing (BAM); 2University of Illinois at Urbana-Champaign; 3Argonne National Laboratory
With the establishment of X-ray photon correlation spectroscopy (XPCS), the in-situ exploration of the structural evolution of metallic glasses became accessible. While the technique serves as a powerful experimental tool for identifying the momentary relaxation response of the amorphous structure in physical aging experiments, it also allows for tracking crystalline contributions over time.Here, we explore the structural evolution of a Zr-based bulk metallic glass under annealing at a temperature very close to its glass transition region over a time frame of more than three days by XPCS. By choosing an appropriate scattering vector the evolution of both the crystalline and amorphous contributions is tracked throughout the experiment. While the momentary time scale of structural relaxation reflects the hallmarks of physical aging, the contrast capturing short time-scale dynamics exhibits unexpected fluctuations along the isotherm. We discuss the evolution of these data in terms of their connection to the crystallization process.
High-resolution Transmission Electron Microscopy Study of Rejuvenation in Bulk Metallic Glasses: Iurii Ivanov1; Lindsay Greer1; 1University of Cambridge
Even for a single composition, bulk metallic glasses (BMGs) offer access to a wide range of structures and properties. There is particular interest in rejuvenation of BMGs to higher-energy states, as this improves their plasticity; lack of ductility impedes the wider exploitation of BMGs. Rejuvenation methods include: fast re-quenching, elastostatic loading, heavy plastic deformation, and cryothermal cycling (of particular interest as an easily applied, shape-preserving method). Characterization of these structural changes remains challenging. We present methods by which BMG rejuvenation can be characterized by transmission electron microscopy (TEM): electron diffraction (ED), and aberration-corrected high-resolution TEM (HRTEM). We focus on rejuvenated Zr-based BMGs. ED provides information on the average volume per atom and on characteristic features of the short-range and medium-range order (SRO and MRO) at the microscale. In complement to this, HRTEM allows extraction of such information locally (at nanoscale) with atomic resolution.
Pressure Effects in Zr-based Super-cooled Liquids: Wojciech Dmowski1; Stanislaw Gierlotka2; Geun Hee Yoo3; Eun Soo Park3; Takeshi Egami1; 1University of Tennessee; 2Polish Academy of Science; 3Seoul National University
Applying high pressure in the supercooled liquid of Zr-based glasses results in structural rearrangements that change local-short range atomic order. This affects thermo-mechanical properties of glasses formed by quenching under pressure. At room temperature and ambient pressure these glasses have higher density, larger Young’s modulus and hardness. Their relaxation spectra are distinct from annealed or equilibrated glasses suggesting a new thermal state. Upon heating at ambient pressure, it is observed that on approaching Tg, these glasses increase their volume, expanding relatively more than as cast samples. Together with density data, this confirms the idea that hydrostatic pressure in the SCL region leads to a new state with higher density and better packing. The observed structural effects can be rationalized by idea that in Zr-based glasses Zr-covalency competes against tendency of close packing. Supported by the U.S. Department of Energy, Basic Energy Sciences, Materials Science and Engineering Division.
Phenomenology of Viscosity and Transport in a Model Fragile Metallic Glass: Peter Derlet1; Hugo Bocquet1; Robert Maass2; 1Paul Scherrer Institut; 2BAM
How thermally activated structural excitations quantitatively mediate transport and micro-plasticity in a model binary glass at the micro-second time-scale is revealed using atomistic simulation. It is found that such local excitations admit a far-field shear-stress signature and underlie the transport of free volume and bond geometry. Viscosity estimates are obtained giving a relaxation time-scale that is comparable to the strain recovery timescales seen in the micro-plasticity simulations. The transport is found to correspond to the evolution of a disclination network describing the spatial connectivity of topologically distinct bonding environments, demonstrating the important role of geometrical frustration in both glass structure and its underlying dynamics.
Mechanisms of Strain-hardening in Metallic Glasses: A. Lindsay Greer1; Y. Li2; A. Inoue3; 1University of Cambridge; 2Institute of Metal Research; 3Josai International University
In contrast to conventional polycrystalline alloys, metallic glasses (MGs) are generally expected to soften under plastic deformation, impeding their wider application. While there have been many hints that MGs might show strain-hardening in particular circumstances, it is only recently [1] that the expected correlation of strain-hardening and suppression of shear-banding has been confirmed for unconstrained deformation. The gradient of the plot of flow stress as a function of strain, normalized by the initial yield stress, characterizes the efficiency of strain-hardening of a material. For a conventional stainless steel and for many polycrystalline alloys, this efficiency is approximately 7. In highly rejuvenated MGs [1], this is approximately 45. Very recent measurements, on MGs that show deformation-induced crystallization, reveal hardening efficiencies as high as 300. We explore the origins and applicability of such rapid strain-hardening.[1] J. Pan, Yu.P. Ivanov, W.H. Zhou, Y. Li, A.L. Greer, Nature 578 (2020) 559‒562.
Metallic Glacial Glass Formation by a First-order Liquid-liquid Transition: Yonghao Sun1; 1Institute of Physics, the Chinese Academy of Sciences
The glacial phase, with an apparently glassy structure, can be formed by a first-order transition in some molecular-glass-forming supercooled liquids. Here we report the formation of metallic glacial glass (MGG) from the precursor of a rare-earth-element-based metallic glass via the first-order phase transition in its supercooled liquid. The excellent glass-forming ability of the precursor ensures the MGG to be successfully fabricated into bulk samples (with a minimal critical diameter exceeding 3 mm). Distinct enthalpy, structure, and property changes are detected between MGG and metallic glass, and the reversed “melting-like” transition from the glacial phase to the supercooled liquid is observed in fast differential scanning calorimetry. The kinetics of MGG formation is reflected by a continuous heating transformation diagram, with the phase transition pathways measured at different heating rates taken into account. The finding supports the scenario of liquid–liquid transition in metallic-glass-forming liquids
Strain-dependent Shear-band Structure in a Metallic Glass: Robert Maass1; 1Federal Institute for Materials Research and Testing (BAM)
It is well known that strain localization into shear bands in metallic glasses induces local structural changes at the nanoscale. However, often the characterization of this structural damage is done at random locations where the relation between a local observable and the admitted shear strain is unclear. Here we address the question of strain-dependent shear damage in a Zr-based bulk metallic glass (Scripta Materialia 190 (2021) 75). Analyzing the shear-band structure of shear- band segments that experienced shear strains covering four orders of magnitude with high-angle annular dark field transmission electron microscopy (HAADF-STEM) reveals strongly scattered data with an overall trend of increasing local volume dilatation with increasing shear strain. Locally, however, a variety of trends is observed, which underlines the strong heterogeneity of structural damage in shear bands in metallic glasses.
Crystallization of a Au-based Bulk Metallic Glass: Influence of the Initial Glassy State: Owain Houghton1; Yurii Ivanov1; A. Lindsay Greer1; 1Dept. Materials Science & Metallurgy, University of Cambridge
On heating, a bulk metallic glass (BMG) first enters the supercooled-liquid region, and then crystallizes. Conventionally, the state of the BMG is considered irrelevant for crystallization; the supercooled liquid has no ‘memory’ of the initial glass. The Au49Pd2.3Ag5.5Cu26.9Si16.3 BMG chosen for the present work has been very widely studied, not least because this composition can be melted and revitrified in fast differential scanning calorimetry (FDSC) – this allows characterization immediately after glass formation. These studies show clearly that (contrary to the conventional view) the state of the BMG does affect the crystallization. We use FDSC, HRTEM and STEM characterization to extend the published studies and explore how changes to the glassy state (the extent of α and β relaxation and embedded crystalline nuclei) can affect the crystallization upon heating. The findings are relevant not only for metallic, but also for silicate and perhaps other, glassy systems.
Synchrotron X-ray Diffraction of Metallic Glass Rejuvenated under Triaxial Compression: Nikolaos Panagiotopoulos1; Konstantinos Georgarakis2; Yi Li3; Alan Greer1; 1University of Cambridge; 2Cranfield University; 3Chinese Academy of Sciences
Metallic glasses (MGs) show extraordinary mechanical properties such as high strength and high elastic limit (on the order of 2%) but they lack ductility. One way to improve the ductility of MGs is to ‘rejuvenate’ the amorphous structure, reaching states of higher enthalpy. MGs plastically deformed under triaxial compression can undergo extreme structural rejuvenation. Calorimetric measurements suggest that the highest degree of rejuvenation achieved is equivalent to a casting cooling rate of 1010 K s‒1, and transmission electron microscopy confirmed that significant structural changes can be achieved. The present work extends such studies by using synchrotron X-ray diffraction to map the structural changes across sections of processed bulk MG rods. Measurements of strain parallel and perpendicular to the rod axis reveal complex patterns that reflect both elastic deformation and changes in MG structure. These patterns provide insight into the rejuvenation process activated by the triaxial compression method.
Statistical Analysis on Single Versus Successive Pop-ins in Nanoindentation Tests of Zr-based Bulk Metallic Glass: Priyanka Saini1; Upadrasta Ramamurty2; Jae-il Jang3; R.L. Narayan1; 1Indian Institute of Technology; 2Nanyang Technological University; 3Hanyang University
3-parameter bimodal Weibull distribution best captures the stochastic nature of incipient plasticity in bulk metallic glasses (BMGs). The present study studies successive pop-in events in the load, P, vs. displacement, h, curve which describe further evolution of plasticity in BMGs. Statistical tools like maximum likelihood estimates and Akaike information criterion are extracted from indentation data for the first 3 pop-ins in the P-h curves. It was observed that while the 2nd and 3rd pop-in load distribution is also modelled by the 3-parameter Weibull distribution, the parameters undergo a significant change from that observed for the 1st pop-in load distribution. The effect of structural state and the size of the indenter were also considered to discuss the formation of subsequent shear bands in BMGs.