Bulk Metallic Glasses XIV: Structures and Modeling I
Sponsored by: TMS Structural Materials Division, TMS: Mechanical Behavior of Materials Committee
Program Organizers: Peter Liaw, University of Tennessee; Hahn Choo, University of Tennessee; Yanfei Gao, University of Tennessee; Yunfeng Shi, Rensselaer Polytechnic Institute; Xie Xie, The University of Tennessee; Gongyao Wang, The University of Tennessee; Jianzhong Jiang, Zhejiang University

Thursday 8:30 AM
March 2, 2017
Room: 33A
Location: San Diego Convention Ctr

Session Chair: Karin Dahmen, University of Illinois at Urbana Champaign; Xie Xie, The University of Tennessee, Knoxville

8:30 AM  Invited
Modeling Slips in Solids and Comparison to Experiments: Karin Dahmen1; Michael LeBlanc2; Peter Liaw3; Robert Maass2; Jonathan Uhl4; Wendelin Wright5; Xie Xie3; 1 University of Illinois at Urbana Champaign; 2University of Illinois at Urbana Champaign; 3The University of Tennessee, Knoxville; 4Retired; 5Bucknell University
    Many slowly compressed solids plastically deform with sudden slips, or jumps in the stress-strain curve [1]. We study slip statistics, dynamics, and time series properties under a range of different experimental conditions. We discuss an analytic model and compare its predictions to recent experimental observations. Reference: [1] Jonathan T. Uhl, Shivesh Pathak, Danijel Schorlemmer, Xin Liu, Ryan Swindeman, Braden A.W. Brinkman,, Michael LeBlanc, Georgios Tsekenis, Nir Friedman, Robert Behringer, Dmitry Denisov, Peter Schall, Xiaojun Gu, Wendelin J. Wright, Todd Hufnagel, Andrew Jennings, Julia R. Greer, P.K. Liaw, Thorsten Becker, Georg Dresen, and Karin A. Dahmen, Universal Quake Statistics: From Compressed Nanocrystals to Earthquakes, Scientific Reports 5, 16493 (2015) and references therein. Acknowledgments: We gratefully acknowledge support through NSF grants DMR-1005209, DMS-1069224 and DOE project FE0011194 with project manager Jessica Mullen.

8:50 AM  Invited
On the Proper Determination of Power Law Exponents for Slip Statistics Using Experimental Data from Bulk Metallic Glasses: Wendelin Wright1; Michael LeBlanc2; Aya Nawano2; Xiaojun Gu1; J.T. Uhl3; Karin Dahmen2; 1Bucknell University; 2University of Illinois at Urbana-Champaign; 3Retired
    Universality in materials deformation is a topic of intense interest in microplasticity modeling with a special emphasis on the power law exponents that characterize slip statistics. This work develops guidelines for the experimental conditions required to accurately record slip avalanches and compute power law exponents. Proper determination of the power law exponents requires careful attention to the details of the instrumentation including parameters of low pass filters in the signal conditioning electronics as well as filtering of experimental noise and selection of a sufficient data acquisition rate. Inadequate attention to these details may lead to unresolvable merging of avalanches, loss of small avalanche data, calculation of incorrect exponents, and possibly failure to recognize a power law regime in the data even if one truly exists. We will present purposely down-sampled and improperly filtered data from compression testing of metallic glasses that was otherwise properly acquired to illustrate our findings.

9:10 AM  Invited
The Statistics of Thermally Activated Structural Excitations in a Model Amorphous Solid: Peter Derlet1; Robert Maass2; 1Paul Scherrer Institut; 2University of Illinois at Urbana-Champaign
    The present work uses atomistic simulation to investigate localized structural excitations in model amorphous systems that do not involve a driven material instability. Potential energy landscape exploration methods reveal extended chain like structural excitations, the energy of which is controlled predominantly by the elasticity of the surrounding amorphous matrix. This is complemented by very long molecular dynamics simulation runs spanning four orders of magnitude in temperature ramping time-scales. These dynamical simulations demonstrate significant local structural excitations as a function of increasing temperature which are compatible with those found by the static exploration methods, the kinetics of which can be quantitatively understood in terms of a power-law distribution of barrier energies.

9:30 AM  Invited
'Crystal Genes' in Metallic Liquids and Glasses: M. Kramer1; Y. Sun1; F. Zhang1; Z Ye1; Y. Zhang1; X. Fang1; Z. Ding2; C. Z. Wang1; M.I. Mendelev1; R.T. Ott1; K.M. Ho1; R.E. Napolitano1; 1Iowa State University; 2University of Science and Technology of China
    It has been widely speculated that dominant motifs, such as short-range icosahedral order can influence glass formation. Less well understood is how these motifs (crystal genes) in the liquid can influence phase selection upon devitrification. These ‘crystal genes’ are the underlying structural order that transcends liquid, glass and crystalline states. By comparing the amorphous states of the same alloy compositions formed by sputtering and rapid solidification, and their devitrification pathways, we can quantify the distribution of the common packing motifs in the liquid or glass and in stable and metastable phases which form. We will discuss how this approach brings new insight into the origin of vitrification and mesoscopic order-disorder transitions in condensed matter. A genetic algorithm is applied to search for the energetically favourable stable and metastable crystal structures of complex metallic compounds, and a cluster alignment method reveals the most common packing motifs in crystalline and non-crystalline structures.

9:50 AM Break

10:10 AM  Invited
A Comprehensive Study of the Deformation Mechanism of Amorphous CuZr/Nanocrystalline Cu Nanolaminates via Integrated Experiments and Computations: Bin Gan1; William Yi Wang1; Bin Tang1; Jun Wang1; Hongchao Kou1; Maosen Fu1; Jinshan Li1; 1Northwestern Polytechnical University
    Incorporation of crystalline phases into BMG matrix is an effective method to arrest and deflect the propagation path of shear bands and ensure a safe usage of BMG materials. In the present work, nanolaminates consisting of alternating amorphous CuZr and nanocrystalline Cu are selected to investigate the interaction of shear bands with nanocrystallines. Micro-compression technique is utilized to reveal the propagation speed of shear band in amorphous CuZr, the deformation of nanocrystalline Cu, and the chemical intermixing as well as stress-induced crystallization of amorphous phase. The comprehensive study via transmission electron microscopy, atom probe tomography and ab initio molecular dynamics simulations of the deformed micropillars reveals that the grain rotation in the crystalline portion and non-diffusive crystallization in the amorphous layer are responsible for slowing down the movements of shear bands. The underlying mechanism of serrated flow of the nanolaminates is also elucidated in the present work.

10:30 AM  Invited
Modelling and Experimental Assessment of Residual Stress Distribution in Zr-based Bulk Metallic Glass: Marco Sebastiani1; Alexander Korsunksy2; Enrico Salvati2; Tan Sui2; Easo George3; 1Roma TRE University; 2University of Oxford; 3Ruhr-Universitšt Bochum
    Rapid cooling, also referred to as quenching or tempering, is the principal production route for bulk metallic glasses that exhibit high hardness and strength due to their amorphous structure that precludes plastic deformation by easy crystal slip. Importantly, rapid cooling is usually accompanied by the creation of residual stresses that also have a strong effect on the deformation behaviour. The present study aims to obtain insight into the residual stresses in cylindrical samples of Zr-based bulk metallic glass (BMG) by combining analytical modelling of thermal and mechanical problems with experimental measurements using Focused Ion Beam–Digital Image Correlation (FIB-DIC) ring-core milling. The results show good agreement between the two approaches, providing improved confidence in the validity of the two approaches considered here.

10:50 AM  Invited
Universality of Slip Avalanches in a Ductile Bulk Metallic Glass: Junwei Qiao1; Jiaojiao Li1; Huijun Yang1; 1Taiyuan University of Technology
     Intermittent serrated flows of a ductile bulk metallic glass (BMG) at different strain rates is investigated by statistic analysis of stress drops during plastic flows. The scaling behavior, i.e. a complementary cumulative distribution function (CCDF) is predicted universally by simple but wisdom mean-field model (MFT). The remarkable agreement between the measured slip-avalanche magnitudes and MFT prediction indicates that the plasticity for the present Fe-based BMGs can be tuned by imposed strain rates. In addition, this tuned plasticity is illuminated with the free-volume model.

11:10 AM  Student
Structural Stabilities and Mechanical Responses of Ni-transition Metal Binary Glass-forming Alloys: Hehsang Ahn1; Jinwoo Kim1; Soyeon Kim1; Eun Soo Park1; 1Seoul National University
    Ni-based metallic glasses are attractive candidates for structural applications since they exhibit outstanding thermal and mechanical properties. Ni successfully forms an amorphous structure upon alloying with other transition metals (TMs), and glass-forming Ni-TM binary alloys have similar compositions regardless of the kind of TMs. Since glass forming ability (GFA) is closely related to an atomic structure, this unique composition ratio is expected to play a key role in achieving a structure favorable for vitrification. Although the consistent composition ratio is required for enhanced GFA in each system, GFA diverges greatly according to TMs. To understand the correlation between structural stabilities and GFA, we investigated mechanical responses through nanoindentation test on different Ni-TM metallic glasses prepared by melt-spinning. We statistically analyzed the distribution of shear avalanches thereby characterizing amorphous structures in the aspect of topological fluctuations. These results could provide effective guidelines for an alloy design by tailor-made atomic structure control.