Bulk Metallic Glasses XIV: Alloy Development and Application 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

Monday 8:30 AM
February 27, 2017
Room: 33A
Location: San Diego Convention Ctr

Session Chair: Peter Liaw, The University of Tennessee; William Johnson, California Institute of Technology

8:30 AM  Keynote
Buckle Modes: A Simple Model for the Thermodynamics of Configurational Excitations in Metallic Glass Forming Liquids: William Johnson1; 1California Institute of Technology
    Metallic glasses exhibit continuum elasticity thermodynamic properties well described by the classical Debye-Grueneisen theory of solids. The undercooled liquid samples many configurational states (Inherent States), each corresponding to a stable atomic arrangement with characteristic elastic moduli and vibrational properties. The talk surveys ultrasonic data and other experimental results for the high frequency liquid shear modulus, G∞. Separate configurational and vibrational contributions to its temperature and energy dependence are identified. A simple two-state “buckle mode” model is proposed to model liquid thermodynamics. The model divides the splitting energy of a “buckle mode” into a “free” transformation energy term and an Eshelby elastic compatibility term. A self-consistent mean field approximation is used to solve for the thermodynamic properties of the liquid. Comparison with experimental data shows that this model gives a significantly better description of the configurational thermodynamics than the traditional “Gaussian Landscape” picture where a “1/T2” configurational heat capacity is assumed.

9:00 AM  Invited
A Strategy Towards Decreasing the Cost of Humanoid Robotics Utilizing Bulk Metallic Glasses (Part 1): Douglas Hofmann1; Scott Roberts1; Peter Dillon1; 1NASA JPL/Caltech
    The development of gears for high-performance robotics, both terrestrial and planetary, has long been driven by design, the performance of lubricated steel gears, and the precise manufacturing of the gear components. Complex gear designs required in many robotics applications make up the majority cost of the robot, owing to the intricate manufacturing of steel. For space applications, the problem is compounded by extremely low temperatures, which preclude most lubricants. NASA JPL has been developing a unique class of BMG gearboxes for robotics using cutting edge technology for both the alloys and the manufacturing. This talk focuses on the need for low-cost, high-performance gearboxes and will give a status report of the research, including prototyping, alloy development, and testing. We show that BMGs not only have the potential for use as unlubricated gearboxes for space applications, but also as a revolutionary material for decreasing the manufacturing cost of all humanoid robotics.

9:20 AM  Invited
The Development, Manufacturing and Testing of New Robotics Gearbox Enabled by Bulk Metallic Glass (Part 2): Douglas Hofmann1; Scott Roberts1; Peter Dillon1; 1NASA JPL/Caltech
    For the past four years, NASA JPL has been developing a new class of robotics gearboxes using the benefits of BMG compared to existing materials. Prototyping has demonstrated the potential advantages of BMGs but scale-up to commercialization had not yet been completed. In the current talk, efforts to commercially manufacture and test a new type of robotics gearbox are presented, including net-shaped casting of new BMG alloys using brand-new injection molding technology as well as limited integration and testing of the resulting hardware. We demonstrate characterization of the materials, integration into existing gear systems to create hybrid gearboxes and we show limited unlubricated operations down to -150 degrees Celcius. The use of BMGs in this particular application shows promise for revolutionizing how high-performance gears are manufactured and operated. A discussion about plans for widespread commercial manufacturing will be presented.

9:40 AM  Invited
Manufacturing of Metallic Glasses by Rapid Discharge Forming: Marios Demetriou1; William Johnson2; 1Glassimetal Technology; 2California Institute of Technology
    While metallic glasses are generally known for their attractive mechanical properties, perhaps their most promising attribute is their potential for “thermoplastic” processing. Unfortunately, this potential is practically limited by the rapidly intervening crystallization of the supercooled liquid. Rapid Discharge Forming (RDF) has recently emerged as an effective means to overcome this limitation. It enables uniform heating to a viscosity regime where conventional thermoplastics are processed (i.e. 100–1000 Pa-s), on millisecond time scales effectively bypassing crystallization. This viscosity regime is optimal for injection molding, allowing low injection pressures yet promoting a stable flow front such that flaws typically arising from flow-front break-up (e.g. voids, seams, flow lines) are effectively suppressed. As such, RDF is performed under stable and homogeneous flow conditions producing fully-amorphous defect-free parts. In this presentation, efforts in scaling up RDF to develop a commercial-ready manufacturing platform will be discussed, and progress in part manufacturing will be presented.

10:00 AM  Invited
Interface-Mediated Monatomic Metallic Glasses Formation Through Ultrafast Liquid Quenching: Li Zhong1; Jiangwei Wang1; Hongwei Sheng2; Ze Zhang3; Scott Mao1; 1University of Pittsburgh; 2George Mason University; 3Zhejiang University
    We report an experimental approach to vitrify monatomic metallic liquids by achieving an unprecedented high liquid quenching rate of 1014 K/s under in-situ transmission electron microscope. Under such a high cooling rate, melts of pure refractory BCC metals, such as liquid tantalum and vanadium, are, for the first time, successfully vitrified to form MGs suitable for property interrogations. With the in-situ TEM observation we investigated the formation condition and thermal stability of the as-obtained monatomic MGs. The availability of monatomic MGs being the simplest glass formers offers unique possibilities to study the structure and property relationships of glasses. Our technique also exhibits great control over the reversible vitrification-crystallization processes, suggesting its potential in micro-electro-mechanical applications. The ultra-high cooling rate, approaching the highest liquid quenching rate attainable in the experiment, makes it possible to explore the fast kinetics and structural behavior of supercooled metallic liquids within the nano- to pico-second regimes.

10:20 AM Break

10:40 AM  Invited
Fabrication and Characterization of Roll Bonded, Laminated Bulk Metallic Glass/Metal Composites: Sina Shahrezaei1; Stephanie O'Keeffe2; Irene Beyerlein3; Suveen Mathaudhu1; 1University of California Riverside; 2Liquidmetal Techologies, Inc.; 3University of California, Santa Barbara
    Monolithic bulk metallic glasses (BMG) are known for their high yield strengths and hardness, however, they are inherently brittle due to their lack of ambient temperature plasticity mechanisms. Layered BMG/metal composites fabricated using vapor deposition methods are reported to have extraordinary mechanical performance including high ductility and strength, however, they are limited in size and scalability due to inherent constraints of deposition processes. Here, we demonstrate the scalable fabrication of multilayer laminated Zr-based BMG/metal composites using roll bonding. The influence of thermomechanical processing parameters on the resultant laminate morphology and bonding is evaluated. Additionally, the nature of the rolled microstructures along with the bulk mechanical properties is presented. These findings will shed light on some of the preferred considerations for uniform co-reduction and enhanced laminate bond strength. The results forecast the design of a variety of BMG/crystalline metal composites for high performance structural materials.

11:00 AM  Invited
Improving the Fracture Toughness of Bulk Metallic Glasses by Thermomechanical Treatments: Jamie Kruzic1; Bosong Li1; Shenghui Xie2; Hamed Shakur Shahabi3; Sergio Scudino3; Jürgen Eckert4; 1UNSW Australia; 2Shenzhen University; 3IFW Dresden; 4Montanuniversität Leoben
    While notched toughness values for bulk metallic glasses (BMGs) tend to be consistently high, large variability has been reported in pre-cracked mode I fracture toughness and such scatter is seen even for a single BMG composition. In this presentation it will be discussed how the observed fracture behavior is related to the internal structure of the BMG samples, and how high toughness behavior can be induced by creating favorable metallic glass structures. The effects of thermomechanical treatments such as cold imprinting, cold rolling, and cryogenic thermal cycling on fracture toughness will be presented. In general, such treatments are shown to 1) ductilize pre-cracked bending beams, 2) reduce the observed scatter in the fracture toughness, and 3) achieve high toughness behavior typical of notched samples. Overall, these results suggest that thermomechanical treatments are an easily accessible means to induce favorable glass structures that promote improved fracture toughness behavior.

11:20 AM  Invited
Formation and Properties of Biodegradable Mg-Zn-Ca-Sr Bulk Metallic Glasses for Biomedical Applications: Shujie Pang1; Haifei Li1; Ying Liu1; Peter K. Liaw2; Tao Zhang1; Haoyan Dia; 1Beihang University; 2University of Tennessee
    Owing to the unique amorphous structure, glassy alloys exhibit high yield strength, low Young’s modulus, and high corrosion and fatigue resistance, which encourage their applications as biomaterials. Among the glassy alloys, Mg-based bulk metallic glasses (BMGs) are attractive as potential biodegradable implantation biomaterials. In this presentation, our findings regarding the syntheses and properties of Mg-based BMGs for potential biomedical applications will be reported. Novel Mg-based BMGs with improved glass-forming ability (GFA) and mechanical properties, suitable corrosion resistance and good biocompatibility were synthesized in Mg-Zn-Ca-Sr alloy system. It was found that the Sr-microalloying could effectively elevate the GFA and corrosion resistance of Mg-based BMGs. The mechanisms for the formation and properties of the Mg-based BMGs will also be discussed. The combination of the high GFA, superior specific strength, suitable and controllable corrosion behaviors, and good biocompatibility indicates the promising potential of the novel Mg-based BMGs to serve as biodegradable implant materials.

11:40 AM  Invited
Critical Cooling Rate versus Critical Heating Rate in BMG-forming Alloys: C.W. Ryu1; Eun Soo Park1; G.W. Lee2; K.F. Kelton3; 1Seoul National University; 2Korea Research Institute of Standards and Science; 3Washington University
    Synthesis of bulk metallic glasses (BMGs) under low cooling rate condition was successfully achieved in various alloy systems with an extremely high thermal stability. In these alloys, the critical cooling rate (CCR) is relatively low. Thus, it is possible to measure the complete Time-Temperature-Transformation (TTT) diagram for the crystallization in the whole temperature range of the undercooled liquid. Furthermore, we can also similarly measure the critical heating rate (CHR) for escaping crystallization during heating, if the alloy exhibits extremely high glass-forming ability (GFA). In the present study, we experimentally measured the TTT diagram of various BMG-forming alloys and their thermophysical properties during cooling and heating using a containerless high temperature/ high vacuum electrostatic levitation (ESL) technique. In particular, we carefully compare the CCR for glass formation and CHR for escaping crystallization. Indeed, these analyses allow us to understand how the undercooled liquid stability and phase transformation depend on key variables.