Bulk Metallic Glasses XVII: Structures and Modeling
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
Thursday 8:30 AM
February 27, 2020
Room: Marina Ballroom G
Location: Marriott Marquis Hotel
Session Chair: Mo Li, Georgia Institute of Technology; Eun Soo Park, Seoul National University
8:30 AM Invited
Correlating Structural Heterogeneity to Properties of Metallic Glasses using Mesoscale Deformation Simulation Incorporating 4D-STEM: Pengyang Zhao1; Soohyun Im1; Geun Hee Yoo2; Eun Soo Park2; Jinwoo Hwang1; Yunzhi Wang1; 1The Ohio State University; 2Seoul National University
We present the new correlation between the mechanical properties and the nanoscale structural heterogeneity that is attributed to the distribution of medium range ordering (MRO) in metallic glasses (MGs). Our novel approach uses mesoscale deformation simulation based on the heterogeneously randomized shear transformation zone (STZ) model, which incorporates the type, size, distribution, and volume fraction of MRO precisely determined using 4-dimensional scanning transmission electron microscopy (4D-STEM). We show that the details of MRO and structural heterogeneity vary significantly with small changes in composition and thermal history, which results in substantial change in measured ductility. The mesoscale simulation provides important insights on how the nanoscale structure in MGs determines the STZ activation and formation of shear bands. The result provides important guidance on how to tune the nanoscale structure to control the ductility of MGs, which can lead to new MGs achieving both high strength and ductility.
8:50 AM Invited
Theoretical Strength and Prediction of Structural Defects in Metallic Glasses: Zhukun Zhou1; Hao Wang2; Mo Li3; 1Central South University; Georgia Institute of Technology; 2Shenzhen University; 3Georgia Institute of Technology,
Theoretical strength plays a pivotal role in gauging the maximum stress and inferring structural defects in crystalline materials. However, its very existence and the expected prediction of possible defects in amorphous solids remain elusive. Here, by using a finite deformation theory, we obtain the theoretical strengths for several bulk metallic glasses under pure shear loading. The theoretical strengths obtained are only several times larger than the experimental yield stresses; in contrast, they are three or four orders of magnitude higher in crystalline materials. This striking closeness between the theoretical and experimental strengths suggests the absence of any extended structural defects that can substantially reduce the intrinsic strength in the amorphous metals. Instead, the atoms have to sever each individual bond to deform. Further investigation reveals that the deformation occurring at the theoretical stress proceeds with the mechanical instability with a vanishing shear modulus, or a mechanical spinodal. We deduce from these results that different fundamentally from crystalline solids, there are no extended structural defects in the amorphous solids and the plastic deformation must be local and sensitive to sample conditions.
9:10 AM Invited
The Physics of an Elemental Ag Glass: First Order Glass Transition and Melting: Qi An1; William Johnson2; Konrad Samwer3; Sydney Corona4; William Goddard2; 1University of Nevada, Reno; 2Caltech; 3University of Goettingen; 4California Institutue of Technology
The glass transition is ubiquitous, while the nature of the glass state has been long been debated. Here, we examined elemental Ag liquid using molecular dynamics (MD) simulations from which the metastable glass state can be achieved in the simulation time scale of nanoseconds. Our MD simulations proof that the glass transition in these liquid metals is a 1st order freezing transition from a high temperature liquid-like disordered phase to a heterogeneous, elastically rigid, low temperature solid-like phase. The robust metastability of glass phase in the MD simulations enables us to apply thermodynamic principles to construct a glass-crystal-liquid phase diagram over a broad range of temperature, as well as the time-temperature-transformation diagrams for nucleation of glass from the liquid, and crystal from the glass. We propose that the first order character of the glass transition is fundamentally linked to the emergence of long-range elasticity and elastic interactions in the glass.
9:30 AM
Molecular Dynamics Simulations of Iron-based Metallic Glasses during Spark Plasma Sintering: Jordan Campbell1; Carlos Ruestes2; Tod Pascal1; Olivia Graeve1; 1University of California, San Diego; 2National University of Cuyo
Bulk metallic glasses are metastable solids that can be manufactured using a variety of techniques, including the spark plasma sintering (SPS) process. This processing technique allows the rapid sintering of a variety of materials and can be used to obtain nanometer grain sizes and metastable phases. In situ analysis of metallic glasses to understand how the atoms diffuse is not possible due to the nature of SPS. Thus, we have studied the process of sintering of these materials using a classical molecular dynamics methodology to elucidate self and mutual diffusion coefficients based on combined Embedded Atom Method (EAM) and Morse potentials. However, as classical molecular dynamics does not explicitly handle electron dynamics, a charge equilibration technique has been used to account for the effect of high current densities (~103 A/cm2 ) inherent in SPS. Specific results on iron-based metallic glasses will be presented and discussed.
9:50 AM Cancelled
Pressure Induced Amorphization in Alloys: Hongbo Lou1; Qiaoshi Zeng1; 1Center for High Pressure Science and Technology Advanced Research
Amorphous materials, without any long-range lattice symmetries, distinct themselves from crystalline materials in every aspect involving properties and structures. Typically, amorphous materials are quenched from high-temperature melt when the cooling rate exceeds a critical value to bypass crystallization. In this talk, we will show our recent work on pressure-induced amorphization (PIA) of several alloys which has not been reported before. By combining experiments and theoretic simulations, the lattice instability is found to play a dominant role in the PIA of these alloys. A more interesting point is the remarkable resemblance in the local structure between the crystalline and amorphous phases, indicating the amorphization is introduced by local atomic rearrangement and the possible existence of long-range packing order of amorphous clusters. This result opens a new window to synthesize amorphous alloys and also provide a model to study the link between amorphous structures and crystalline structures.
10:10 AM Break
10:30 AM
Is Atomic Size-mismatch a Sufficient Condition to Yield Fragility in Bulk Metallic Glass Forming Liquids?: Tina Mirzaei1; Zhichao Yu2; Jamie J.Kruzic3; P.Alex Greaney1; 1University of California, Riverside; 2Oregon State University; 3UNSW
Fragility in a liquid refers to the sensitivity of its bonding network and is associated with non-Arrhenius dependance of the liquid’s viscosity as it approaches the glass transition temperature. In bulk metallic glasses (BMGs), ductility in the glassy state correlate with fragility as a liquid, so understanding the origins of fragility could provide insights into plasticity mechanisms in BMGs. Experimentally, there are qualitative differences in temperature dependance of the medium range order in strong vs fragile liquids. This hints at differences in cooperative packing of atoms, and lead us to ask: is atomic size mismatch sufficient to cause fragility? Presented are a series of molecular dynamics simulations in which known strong and fragile BMGs are represented by hypothetical alloys with the same mixture of atomic radii, but with all atoms interacting via the same bonding. Remarkably, these radii alloys display many of the signatures of fragility as their real-life counterparts.
10:50 AM
The Intriguing Structure of Marginal Glass Forming Alloys: Tolga Han Ulucan1; İlkay Kalay2; Yunus Kalay1; 1Middle East Technical University; 2Çankaya University
Marginal metallic glass-forming alloys exhibit unique devitrification features due to their exceptional primary crystallization products of Al nanocrystals with populations of 1024m-3. A full agreement on how this abnormal nucleation event occurs is still lacking. Our previous studies on Al-RE (RE: rare-earth) have shown that two different amorphous precursors prepared using melt-spinning and magnetron sputtering techniques showed clear differences in phase selection hierarchy upon continuous heating. We believe that this difference is originated from the medium range ordered structure, exist in as-quenched melt-spun ribbon which is inherited from its molten state. In this study we investigated the local structure, chemistry and any possible higher order correlations in the amorphous and liquid state by performing critical high energy synchrotron X-ray Diffraction, EXAFS, ab-initio and Reverse Monte Carlo modelling. RE atoms were found to be highly correlated with Al atoms which results in formation of network dividing the amorphous and liquid matrix.
11:10 AM
Effect of Ni-Nb Metallic Glass on Moderating the Shock Damage in Crystalline Ni-amorphous Ni62Nb38 Nanocomposite Structure: A Molecular Dynamics Study: Kontala Vijay Reddy1; Snehanshu Pal1; 1National Institute of Technology Rourkela
In this atomistic simulation study, the influence of Ni-Nb metallic glass on the dynamic response of crystalline Ni-amorphous Ni62Nb38 nanocomposite under shock loading is investigated. Structural analyses are carried out via different methods i.e. pressure profile, kinetic energy maps, and atomic strain. Results show that lower velocity shocks have minimal impact on the structural transformation whereas higher velocities demonstrate FCC-to-BCC transformation in the specimen. Kinetic energy maps and atomic strain analysis reveal that presence of amorphous phase has helped in subduing the shock propagation by decreasing the shock intensity. Structural transformation in metallic glass is analyzed via Voronoi analysis which shows that icosahedral clusters are disintegrated and higher coordination number clusters are developed under shock loading. Overall, this work can provide fundamental understanding of the atomistic behaviour of crystalline-amorphous nanocomposites/nanolaminate structures under shock loading which can contribute towards designing metallic systems to withstand high impact loads.
11:30 AM Cancelled
Local Structural Signature Underlying Thermally Activated Events in Metallic Glasses: Jun Ding1; Mark Asta2; Robert Ritchie2; 1Xi'an Jiaotong University; 2University of California, Berkeley
Currently, the complex states of metallic glasses can be neatly expressed by the topographic characteristics of the potential energy landscape. However, it remains highly challenging to understand, or even to describe, how the system evolves on the PEL due to its high dimensionality. In this work, we employ molecular dynamics simulation to reveal the local structural signature underlying thermally activated events (beta relaxations) in a variety of metallic glasses. In particular, the activation and relaxation process of thermally activated events are carefully studied to relate with the corresponding local structural environments, including icosahedral order, atomic volume, flexibility volume and atomic-level stress etc. The atomic-level structural anisotropy is also emphasized to relate with the activation of those local events. Our findings thus addresses the pressing need to establish the fundamental understanding of potential energy landscape from the structural perspective. This work was supported by DoE-BES-DMSE, under Contract No. DE-AC02-05CH11231.