Bulk Metallic Glasses XIV: Alloy Development and Application II
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 2:00 PM
February 27, 2017
Room: 33A
Location: San Diego Convention Ctr

Session Chair: Frans Spaepen, Harvard School of Engrg & Appl Sciences; Jinn Chu, National Taiwan University of Science and Technology

2:00 PM  Cancelled
Stress Measurements on Colloidal Glasses: J. Terdik1; David Weitz1; Frans Spaepen1; 1Harvard School of Engrg & Appl Sciences
    Colloidal glasses, consisting of micron-size solid spheres suspended in a liquid, have been used to study the mechanims of glass deformation by tracking the particles in space and time with confocal microscopy [1]. So far, it has been possible only to make strain measurements, based on the relative displacements of the particles. We have now developed a method, similar to traction force microscopy, to measure the overall stress in the glass by tracking the elastic deformation of a gel substrate of known stiffness during the deformation. This technique can be used to determine stress-strain curves, to identify yield points, and to study stress relaxation. Simultaneous access to the motion of all the particles then makes it possible to link the macroscopic mechanical behavior directly to local particle rearrangements. [1] K.E. Jensen, D.A. Weitz and F. Spaepen, Phys. Rev. E 90, 042305 (2014)

2:30 PM  Invited
Structure Modulation and Brittle-to-ductile Transition in Metallic Glasses: Juergen Eckert1; 1Montanuniversität Leoben
    Tailoring intrinsic structure modulation and length-scale effects in metallic glasses via thermal, mechanical or thermo-mechanical treatment in order to enhance their plastic deformability requires a systematic analyzing strategy. Although various achievements were made in the past years to enhance the properties of different BMG alloys, the influences of different treatments utilized for structure modulation and their impact on shear band nucleation and propagation and the brittle-to-ductile transition of metallic glasses are still not fully understood. The present work presents experimental and modeling attempts for deriving design aspects of metallic glasses with respect to short- and medium-range order modulation, precipitation of secondary phases and via modulating internal stresses / strains on different length-scales. The effectiveness of such treatments for plasticity improvement will be analyzed in the light of dynamic structural changes and inhomogeneous stress / strain distributions and their impact on shear band formation and propagation.

2:50 PM  Invited
Thin Film Metallic Glasses: Novel Diffusion Barrier Materials for Solar Cell and Electronic Packaging Applications: Chia-chi Yu1; Cheng-Min Lee1; Chia-Lin Li1; Chia-Hao Chang1; Jinn Chu1; 1National Taiwan University of Science and Technology
    Thin-film metallic glasses (TFMGs) having excellent mechanical properties owing to their amorphous nature are considered to be one of the important emerging metallic coatings. It is known that, in metal materials, the diffusion coefficient in grain boundaries is much higher than that in the bulk, and the former accordingly dominates the diffusion in the Mo/CIGS layer structure of the CIGS solar cell. Therefore, TFMG is suitable for use as a barrier because of the grain-boundary-free structure. The detrimental Fe diffusion from stainless steel (SS) substrate into CIGS is found to be effectively hindered by a 70-nm-thick TFMG barrier; the cell performance is thus improved. Compared with the 2.73% of CIGS on bare SS, a higher efficiency of 5.25% is obtained for the cell with the TFMG barrier. In this presentation, the TFMG as an effective diffusion barrier will be also reported for Sn whisker mitigation in electronic packaging.

3:10 PM  
Improving the Glass Formation and Mechanical Behavior of Ni-free TiZr-based Bulk Metallic Glasses by Ga Additions: Mariana Calin1; Supriya Bera1; Ramasamy Parthiban1; Mihai Stoica1; Jürgen Eckert2; 1IFW Dresden; 2Montanuniversität Leoben
    In the present work the influence of Ga additions on glass forming ability, thermal stability and mechanical behavior of Ti40Zr10Cu36-xPd14Gax (x=2, 4, 8 and 10 at.%) bulk metallic glasses (BMG) was thoroughly studied by a combination of X-ray diffraction, differential scanning calorimetry, mechanical tests and ultrasonic measurements. Ti40Zr10Cu34Pd14Ga2 BMG shows the best combination of mechanical properties, with a plastic strain of about 5 % and maximum compressive strength exceeding 2000 MPa. Comparing the Young’s moduli of Ga-containing Ti-alloys in glassy and crystalline states we found that the glassy state shows significant elastic softening. The Young’s moduli of BMGs at the same compressive strength are about 45% lower than for crystalline counterparts. The unusual combination of low modulus and high strength of these novel Ni-free Ti-based glassy alloys could potentially ameliorate the stress shielding concerns associated with bone fixation devices. Financial support through the EC (FP7 VitriMetTech) is gratefully acknowledged.

3:30 PM Break

3:50 PM  Student
Minimizing Losses in Ferromagnetic Metallic Glass Power Transformers: Michael Floyd1; Marios Demetriou2; William Johnson1; 1California Institute of Technology; 2Glassimetal Technology
    Currently, 3% of losses in the United States’ electrical grid come from power transformers. Owing to high saturation magnetizations and low coercive forces, ferromagnetic metallic glasses are currently offered as a solution to limit such losses. But are the commercially offered micron-thick ribbon cores the best geometry to mitigate these losses? In this work, we analyzed the effect of thickness on the losses in Fe68Mo4Ni3Co5Si1P11.5C5B2.5 as a function of frequency and magnetization, and found the optimal characteristic thickness to exhibit a logarithmic dependence on frequency. Optimal thicknesses are found to range from 400µm for frequencies on the order of 100 Hz to 100µm for frequencies of ~1 GHz. These characteristic thicknesses are larger than the 50µm range currently achievable with commercial melt spinning approaches. Anomalous losses, which dominate over classic eddy current losses in some geometries, account for the optimal character thicknesses in this range.

4:10 PM  Invited
Property Enhancement of BMG Based Nanoglasses Prepared by RF Sputtering of Thin Films: Hans Fecht1; Pierre Denis1; 1Ulm University
    So-called “nanoglasses” are considered non-crystalline solids which exhibit a glass-like atomic structure and contain a significant amount of internal interfaces. This metastable state of matter can be synthesized by thin film deposition from a BMG-type target at appropriate processing conditions. Remarkably, such BMG based nanoglass specimen clearly exhibit an anomaly of the specific heat typical for the nature of the glassy state. By variation of the argon back pressure the resulting nanostructures in the fully amorphous films can intentionally be varied from fully amorphous (2 microbar) to a nanoglobular structure / nanoglass (15 microbar) and to columnar structures at about 100 microbar Argon base pressure. While in general glassy structures lack ductility, the nanoglass state exhibits superior mechanical properties and, at the same time, achieves a remarkable level of ductility. Nanoindentation and stress measurements using cantilever beams clearly indicate some of the underlying mechanisms in ductilizing inherently brittle amorphous materials.

4:30 PM  Invited
Design and Development of Catalytic Amorphous Metals for Energy Conversion and Environmental Remediation: Sundeep Mukherjee1; 1University of North Texas
    Materials for catalytic applications require large electrochemical surface area together with desirable chemistry. Accelerated development of low-cost electro-catalysts necessitates efficient synthesis of hierarchical structures with morphologies that provide high dispersion and effective utilization of the active species. Metallic-glasses are attractive for energy conversion and environmental remediation due to their unique combination of desirable properties and processing ability. They can be synthesized in a wide range of compositions that are not available in crystalline form, which allows continuous control of their electronic and catalytic properties. We have demonstrated that by starting with a homogeneous and isotropic material, the chemistry and morphology can be tuned to obtain hierarchical nanostructures with high catalytic activity. In addition, metallic glasses were found to be very effective in environmental remediation. We have demonstrated rapid dissociation of toxic organic chemicals by metallic glasses, where the amorphous structure and bi-functional mechanism from transition metals play critical roles.

4:50 PM  
Manufacturing of Cu-based Metallic Glasses Matrix Composites by Spark Plasma Sintering: Sandrine Cardinal1; Jean-Marc Pelletier1; Guoquiang Xie1; Jichao Qiao1; 1INSA
    Bulk metallic glasses (BMGs) present high strength, high hardness, superior elastic limits and high wear resistance. However, usually they do not exhibit any significant macroscopic plasticity since the plastic deformation is localized in narrow regions termed shear bands. This lack of macroscopic plasticity limits their structural applications at room temperature. In order to enhance the ductility, metallic glass matrix composites (MGMCs) composed of (a) soft crystalline phase(s) and a glassy matrix have been developed. The ductile crystalline particles act as obstacles for shear bands and hence hamper the rapid propagation of a detrimental shear band. In this study, MGMCs are produced by mixing a metallic glass powder (Cu-based) and a crystalline powder (Zr) in a planetary ball mill and then by densification of the mixture by spark plasma sintering (SPS). The influence of volume percentage of particles on the mechanical properties has been studied.