Copyright (c) 2009 All rights reserved. http://works.bepress.com/kcchen Recent documents in Katherine C. Chen en-us Thu, 27 Aug 2009 09:54:46 PDT 3600 http://works.bepress.com/kcchen/34 http://works.bepress.com/kcchen/34 Mon, 06 Oct 2008 14:49:08 PDT In response to the need to create a skilled workforce in nanotechnology and to excite young students with the wonders and potentials of science, the National Center for Learning and Teaching in Nanoscale Science and Engineering, is developing educational materials for grades 7 - 16. Learning theory and cutting-edge research are used in the development of modules on nanoscience and nanotechnology. This paper describes the rationale for such materials and describes an introductory module in which students are lead through a series of inquiry-based and hands-on activities, which lead to a design project. Its goal is to teach an underlying principle in nanoscience and nanotechnology--the significance of the surface-area-to-volume ratio as objects get very small. The first section of the module investigates how the physical form of a material can influence the degree to which an object interacts with its environment. Different forms of different materials (steel, superabsorbent polymer, and sugar) are investigated as a function of dimensionality and size. The second section is centered on math tools needed to express very small quantities, viz., powers of 10 and scaling, and we intend that students get a feel for how small "nano" is. Shape and size effects on surface areas and volumes are explored in the third section. Graphs illustrate how the surface area to volume ratio changes with size. Consequences of such a trend are discussed in readings about nature and new technologies. The culminating event is an open-ended design project that incorporates the concepts from the previous activities and facilitates engineering design skills. Preliminary field testing has yielded both qualitative and statistical results. Maynard Valerie Conference Proceedings http://works.bepress.com/kcchen/33 http://works.bepress.com/kcchen/33 Mon, 06 Oct 2008 14:48:45 PDT This is the final report of a three-year, Laboratory Directed Research and Development (LDRD) project at Los Alamos National Laboratory (LANL). The goal of the project was to develop methodologies in which to define and improve the properties of NbCr2 so that the high temperature structural applications of alloys based upon this would not be limited by the low-temperature brittle behavior of the intermetallic. We accomplished this task by (1) understanding the defect structure and deformation mechanisms in Laves phases, (2) electronic and geometric contributions to phase stability and alloying behavior, and (3) novel processing of dual phase (Laves/bcc) structures. As a result alloys with properties that in many cases surpass superalloys were developed. For example, we have tailored alloy design strategies and processing routes in a metal alloy to achieve ambient temperature ultimate strengths of 2.35 GPa as well as ultimate strengths of 1.5 GPa at 1000°C. This results in one of the strongest metal alloys that currently exist, while still having deformability at room temperature. Dan J. Thoma Articles http://works.bepress.com/kcchen/31 http://works.bepress.com/kcchen/31 Mon, 06 Oct 2008 14:48:09 PDT National leaders in science and technology sectors speak in unison as they call for engineers who are not only technically competent in their fields, but who possess the abilities to communicate well, to work on teams, to apply systems thinking, to operate in the global business environment, to design within a greater set of constraints (environmental, health and safety, sustainability, economic, societal, political, manufacturability, and ethical). In short, our challenge is to educate an engineering professional who is far more sophisticated than the engineer of the 20th century. Additionally, challenges brought on by the overuse of natural resources put a special responsibility on materials science and engineering (MSE) faculty, whose role it is to assist in shaping the MSE profession. How can faculty deliver relevant curricula for the MSE engineering professional in an already crowded curriculum? Certainly curricular content must be up-to-date. However, a number of the goals can be met through changing the way in which the curriculum is delivered. In particular, we have emphasized mastery at the lower levels to increase retention, and implemented a number of learning "best practices". Our preliminary results are promising: within one year, we were able to reverse a five-year trend in declining enrollment; we have just finished our fourth consecutive year of 100% on-time completions of senior projects; students exhibit a shift in mindset towards a greater awareness of their professional responsibility to serve humanity. In this paper, we will provide a survey of the techniques that we have used along with some preliminary results from our program. Linda Vanasupa Conference Proceedings http://works.bepress.com/kcchen/32 http://works.bepress.com/kcchen/32 Mon, 06 Oct 2008 14:46:14 PDT Despite a rich body of research on factors contributing to attrition of women during the college, women continue to be underrepresented in the graduating classes of most traditional engineering disciplines. We present our Four-Domain Development Diagram (4DDD) in an attempt to enable a systems approach to managing all the factors that contribute to retention. This diagram makes explicit the connections between the learners' response factors in the learning environment, including motivation, interest, and ultimately retention. Although we are only three years into our use of the diagrams' relationships, we have seen a lower overall net attrition rate (male and female) from freshman year from ~50% to ~20%, seeing a net influx of female students, from numbers as low as 2 of 44 in the entering freshmen cohort to 6 out of 40 (now sophomores) in that same cohort. In this paper, we present the diagram, briefly introduce the theoretical underpinnings with preliminary quantitative and qualitative data. Linda Vanasupa Conference Proceedings http://works.bepress.com/kcchen/23 http://works.bepress.com/kcchen/23 Fri, 03 Oct 2008 14:59:58 PDT The effects of Be additions on the oxidation behavior of β-NiAl in moist air at 1000°C and borderline alumina-forming y (TiAI) + Laves Ti-Al-Cr based alloys at 800°C and 1000°C in dry and moist air were investigated. The addition of Be to β-NiAl suppressed the formation of transient alumina, and resulted in the formation of a protective BeAl2O4 spinel phase. In dry air, the addition of Be to the Ti-AI-Cr alloys also resulted in the formation of a protective BeAl2O4 spinel phase. In moist air, only Ti-AlCr- Be alloys with a high Cr content (10 to 15 a/o) formed the protective BeAl24scale. R. H. Hanrahan Jr. Articles http://works.bepress.com/kcchen/22 http://works.bepress.com/kcchen/22 Fri, 03 Oct 2008 14:59:54 PDT P. G. Kotula Articles http://works.bepress.com/kcchen/24 http://works.bepress.com/kcchen/24 Fri, 03 Oct 2008 14:59:49 PDT Systematic studies of alloys based on TiCr, have been performed in order to improve the toughness of Laves phase intermetallics. The extent to which alloy compositions and annealing treatments influence the toughness was quantified by Vickers indentation. The single-phase Laves behavior was first established by studying stoichiometric and nonstoichiometric TiCr,. Next, alloying effects were investigated with ternary Laves phases based on TiCr2. Different microstructures of two-phase alloys consisting of (Ti,Cr)-bcc+TiCr2, were also examined. Various toughening theories based on vacancies, site-substitutions, crystal structure (C14, C36, or Cl5) stabilization, and the presence of a second phase were evaluated. The most effective factors improving the toughness of TiCr2, were determined, and toughening mechanisms are suggested. Katherine C. Chen Conference Proceedings http://works.bepress.com/kcchen/29 http://works.bepress.com/kcchen/29 Fri, 03 Oct 2008 14:59:22 PDT A two-phase, NbCrTi alloy (bcc + C15 Laves phase) has been developed using several alloy design methodologies. In efforts to understand processing-microstructure-property relationships, different processing routes were employed. The resulting microstructures and mechanical properties are discussed and compared. Plasma arc melted (PAM) samples served to establish baseline, as-cast properties. In addition, a novel processing technique, involving decomposition of a supersaturated and metastable precursor phase during hot isostatic pressing (HIP), was used to produce a refined, equilibrium two-phase microstructure. Quasi-static compression tests as a function of temperature were performed on both alloy types. Different deformation mechanisms were encountered based upon temperature and microstructure. Katherine C. Chen Conference Proceedings http://works.bepress.com/kcchen/28 http://works.bepress.com/kcchen/28 Fri, 03 Oct 2008 14:58:58 PDT A metastable, disordered bcc phase has been formed from the melt in a Cr-rich alloy of the Nb-Cr-Ti system, where large volume fractions of the Laves phase would develop under equilibrium solidification conditions. X-ray diffraction (XRD) studies and lattice constant determinations confirm that the melt-spun ribbons contain a bcc phase beyond its terminal solid solution limits. Solidification pathways are proposed based upon metastable and equilibrium phase diagrams. Microstructures have been studied using optical microscopy, scanning electron microscopy (SEM), and transmission electron microscopy (TEM). Cross-sectional TEM reveals tiny, dispersed Laves phase precipitates within the metastable bcc grains near the chill (wheel) side. Away from the wheel, the microstructure changes to a dendritic structure of the bcc and CI5 Laves phase. Annealing of the melt-spun ribbons produces a fine, two-phase microstructure of the equilibrium phases. Microstructures from the melt-spun and arc-melted processing conditions are compared. The microstructural control afforded through this metastable processing route enables a methodology to tailor phase distributions for optimized toughness in Laves phase alloys. Katherine C. Chen Conference Proceedings http://works.bepress.com/kcchen/27 http://works.bepress.com/kcchen/27 Fri, 03 Oct 2008 14:58:35 PDT Various effects on the room-temperature mechanical properties of TiCr2-base alloys have been assessed in efforts to improve the toughness of Laves phase intermetallics (AB2). Systematic studies were performed on: (i) single-phase stoichiometric and nonstoichiometric TiCr2, (ii) TiCr2-base ternary Laves phases, and (iii) two-phase binary alloys containing TiCr2. In order to make quantitative comparisons among the different alloys, Vickers indentation was used to obtain hardness and fracture toughness values. Within the single-phase field, constitutional defects accounted for the compositional dependencies of properties, and may aid the synchroshear deformation process. Ternary Laves phases comprised of Fe, Nb, V or Mo additions to TiCr2 indicated that alloying elements which partition to both A and B sublattices can improve the toughness. Stabilization of the cubic C15 crystal structure also resulted in higher toughness values. Small amounts of the bcc β-phase effectively reduced crack lengths in the Laves phase, and two-phase alloys of (Ti,Cr)+TiCr2 exhibited significant improvements in toughness. Katherine C. Chen Articles