Bonding, Structure, Defects and Diffusion in ‘Tough’ IronBased Bulk Amorphous Alloy

Friday, September 26, 2008 3:00 – 4:00 pm
Room 610, M&M Building

Prof. Gary J. Shiflet
Department of Materials Science and Engineering, University of Virginia

Abstract

Can brittle bulk metallic glasses be further designed to exhibit fracture toughness?And, can this be done without loss of other superior properties, such as, strength(currently 4 GPa)? Yes to both questions. Bulk amorphous metals are quitecommon today and nearly every major metal alloy system can be synthesized intoa bulk glassy material (Fe-, Cu-, Ni- Ti-, Zr-, Mg-based, etc., but not Al). To beuseful, the task now is to make them damage tolerant. This talk will emphasize ourstrategy for increasing alloy plasticity through bonding studies and current effortsto understand defects and structure in amorphous iron-metalloid alloys.  Thedesign of amorphous steel with high glass formability has provided the base alloycomposition used to further improve overall plastic behavior by reducing its highshear modulus. Our systematic investigation highlights the role of interatomicinteractions, in addition to the individual alloying elements, in determining theelastic moduli or Poisson’s ratio, and hence the ductility. For instance, as asolution to alloy brittleness for amorphous steel, ab initio quantum chemistrymethods and EELS indicate that phosphorous improves plasticity because of theunusual bonding associated with electron transfer from phosphorous to iron.Extensions to other alloy systems will also be discussed to test this fundamental approach.

Biography

Dr. Shiflet is currently the WG Reynolds Professor at the University of Virginia where he has been afaculty member in the School of Engineering since 1980. He has a BS and MS in physics and PhD in metallurgicalengineering (1981), all from MTU. Shiflet’s primary interests are in solid-state phase transformations of metal alloysand concerns thermodynamics, nucleation and the kinetics associated with growth of new phases. He haspublished more than 250 papers and holds several patents concerning various amorphous metal alloys. Dr. Shiflethas been awarded two creativity awards from the National Science Foundation, the ASM Research Award (SilverMetal) and has been elected as a Fellow of the American Society for Materials and Japan Advancement of Scienceand was selected as Scientific American 50 for 2004. He is a member of The Metallurgical Society of AIME and theAmerican Society for Materials.

Technical Feasibility Assessment of Bio-absorbable Metal Stent

Tuesday, September 23, 2008 1:00 – 2:00 pm
Room U113, M&M Building

Jon Stinson
Boston Scientific
Interventional Cardiology Division
Maple Grove, MN 55311

Abstract

Boston Scientific Interventional Cardiology Division is exploring the feasibility ofbiodegradable metal stents. In particular, iron is of interest based on reportedbiocompatibility and degradation rate. Boston Scientific is performing IR&Dexperimentation to generate data upon which a recommendation can be made tothe investment board regarding the technical viability of this stent concept. One ofthe challenges discovered was that in-vitro degradation rates of the candidatemetals do not agree with observations from in-vivo experiments. One of the keydesign criteria for a degradable stent is the degradation behavior. In order to beable to assess the feasibility of these stent materials, it is necessary to understandthe time rate of mass and strength loss.

Biography

Jon Stinson is a manager at R&D Materials Analytical Lab, Boston ScientificInterventional Cardiology Division. He received a B.S. degree in Metallurgical Engineering atMTU in 1982 and MBA Management degree at the University of St. Thomas in 1992.  Jon firstworked for 12 years in aerospace and defense (Williams International, Howmet, Honeywell,Alliant Techsystems) as a metallurgical engineer on R&D projects for gas turbine engines andordnance. Then he worked for 14 years in the medical device industry as a metallurgicalengineer and materials lab manager on R&D projects for intraluminal catheter, guidewire, andimplant products.

Enhancement of Magneto-Optical Effects in Gyrotropic Photonic Bandgap Materials

Friday, September 19, 2008 3:00 – 4:00 pm
Room 610, M&M Building

Dr. Amir A. Jalali
Department of Physics
Michigan Technological University

Abstract

Magneto-optic materials have many applications in a large variety of areas of integrated optics. Perhapsthe most common application of magneto-optic materials is in the construction of nonreciprocalwaveguides and magneto-optic isolators although there are also many applications in other areas ofintegrated optics such as magneto-optical fast switching, magneto-optical read-out disks, and magnetooptical sensors and visualizers. All of these applications are based on the magneto-optical activity of thematerial like polarization rotation of the light passing through the medium (Faraday rotation) andmagneto-optical tunability of the medium. Magneto-optical effects can be enhanced significantly in aperiodic structure, the so called photonic crystals, that exhibit photonic bandgaps. The enhancement ofmagneto-optical effects would thus allow large improvements in existing applications and even moreopen up new possibilities for advanced sensor devices and optical filters.

In this talk I will present a study of polarization rotation enhancement in one- and two-dimensionalphotonic crystals and provide theoretical and experimental support for a novel type of photonic bandgapin birefringent magnetooptic photonic crystal waveguides. Contradirectional coupling of fundamental tohigher order local normal modes in birefringent magnetooptic photonic crystal waveguides leads topartially overlapping gyrotropic bandgaps inside the Brillouin zone. The overlapping of gyrotropicbandgaps results in selective suppression of Bloch mode propagation. This type of photonic bandgapand degeneracy breaking inside the Brillouin zone are a result of the local coupling between differentelliptically polarized photonic states in magneto-photonic crystals. Large magnetically active changes inBloch mode polarization near the band edges are observed. These changes are not due to photontrapping as conventionally explained in other types of magnetooptic periodic systems.

The ability of magneto-optic photonic crystal waveguides to provide large polarization rotation and tightoptical confinement can also be exploited to produce highly sensitive biochemical sensors. Our studyshows that the polarization rotation at the edge of gyrotropic degenerate bandgaps is highly sensitive tosmall refractive index changes in the waveguide cover of the device.

Biography

Dr. Jalali received the PhD degree in Physics from the Royal Institute of Technology (KTH), Stockholm, Sweden, inNov. 2004. He spent two years as a Postdoctoral researcher at the Michigan Technological University, Michigan, USA. Since2007, He has been a Research Scientist at Michigan Technological University. His research interests are magnetooptic photoniccrystals, ferromagnetic resonance, waveguide technology and photonic biosensors.

Processing and Properties of Amorphous Reinforced Crystalline Matrix Composites in Ni-W Alloy System

Friday, September 5, 2008 3:00 – 4:00 pm
Room 610, M&M Building

Alex O. Aning
Virginia Polytechnic Institute & State University
Department of Materials Science & Engineering
Blacksburg, Virginia 24061

Abstract

Metal Matrix Composites (MMCs) are used as structural materials because of their ability tohave a combination of high strength and good ductility.  A common problem with MMCs utilizingvastly different materials is the difficulty in forming a strong matrix/reinforcement interfacewithout suffering extensive dissolution, debonding, or chemical reactions between thecomponents.  By using a reinforcement which has a similar chemistry and local atomic structureto that of the matrix, these critical problems can be reduced.  In this work, a nickel baseamorphous particulate reinforced crystalline nickel matrix composites were processed.  Thereinforcement, an equimolar NiW amorphous powder, was synthesized in a SPEX mill by themechanical alloying process.  The amorphous and crystalline nickel powders were blended inan Attritor mill in varying volume fractions and then consolidated using: hot-isostatic pressing(HIP), or combustion driven compaction (CDC) process.  This work revealed that the amorphousNiW reinforcement provided strength and hardness to the ductile Ni matrix while simultaneouslymaintaining a strong interfacial bond due to the similar chemistry of the two components.  Thestrengthening achieved in the composite is attributed to particulate/matrix boundary strengthening.

Biography

Dr. Alex O. Aning is an Associate Professor of Materials Science and Engineeringat Virginia Tech.  He obtained the BS degree in Physics from Morgan State University,Baltimore in 1977, and Ph.D. in Metallurgical Engineering from University of Missouri- Rolla in1982.  After a year of post-doctoral studies at Rolla he joined the Physics Department at MorganState in 1983.  At Morgan State he helped develop a new engineering school.  He later becamethe head the Electrical Engineering Department and lead it to become ABET accredited on thefirst attempt.  He joined Virginia Tech in 1992; from 1998 to 2005, he was part of theEngineering Education Department.  He has held visiting professorships at the Johns HopkinsUniversity (1992) and the University of Virginia (1989/90).  He does research in the areas ofphase transformations, and synthesis and processing of metallic, ceramic and compositematerials.  His current activities include solid-state formation of bulk amorphous alloys, andamorphous phase-strengthened metal matrix composites.  He is a member of TMS and ASMInternational.