Copyright (c) 2010 All rights reserved. http://works.bepress.com/kcchen Recent documents in Katherine C. Chen en-us Wed, 22 Dec 2010 01:34:23 PST 3600 http://works.bepress.com/kcchen/36 http://works.bepress.com/kcchen/36 Mon, 20 Dec 2010 10:53:39 PST Austenitic (B2) NiTi samples were cathodically charged with various amounts of hydrogen. Trends are tracked based on temperature, time and voltage throughout the process to establish consistent and predictive hydrogen charging procedures. The effect of hydrogen on the austenitic structure and the formation of hydrides are studied with x-ray diffraction (XRD). An increase in the austenite lattice parameter with increased hydrogen content is observed up to a hydrogen solubility limit of approximately 85 wppm. At greater hydrogen concentrations, additional XRD peaks appear, suggesting possible hydride formation. Differential scanning calorimetry (DSC) results show a decrease in both the austenitic and martensitic transition temperatures with increased atomic hydrogen content and increased hydride phase. Scanning electron microscopy (SEM) is used to reveal the hydride phase. The effect of atomic hydrogen on NiTi and the structure of the hydride phase are compared with previous hydrogen studies. Amanda Runciman Conference Proceedings http://works.bepress.com/kcchen/35 http://works.bepress.com/kcchen/35 Mon, 19 Apr 2010 14:54:10 PDT One of the inherent challenges of teaching any emerging technology like nanotechnology, is the fact that its core competencies flux in the new disciplines' early stages. Nanotechnology presents an additional challenge in that its underpinnings cross multiple traditional disciplinary boundaries. We have designed a course that aims to address some of these challenges through a handful of structural features: team-based learning; a "reverse of the learning pyramid" approach; team-teaching; embedded information literacy techniques; and application-centered content. Our course is organized around four applications that are in their developmental stages: gold nanoshells for cancer treatment; molecular manufacturing; tissue engineering of a vital organ; and a microfluidic glucose sensor. These applications provide natural contexts for learning biology at the cellular level, the molecular level, the organ level and the biological systems level, respectively. They also provide natural contexts to introduce ideas of scientific uncertainty in emerging fields. In this paper, we will present the design features of our sophomore-level course Nanotechnology, biology, ethics and society and some preliminary results. Linda Vanasupa Conference Proceedings 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 http://works.bepress.com/kcchen/26 http://works.bepress.com/kcchen/26 Fri, 03 Oct 2008 14:58:19 PDT P. G. Kotula Conference Proceedings http://works.bepress.com/kcchen/25 http://works.bepress.com/kcchen/25 Fri, 03 Oct 2008 14:57:54 PDT The morphologies and defect structures of TiCr2 in several Ti-Cr alloys have been examined by optical metallography, x-ray diffraction, and transmission electron microscopy (TEM), in order to explore the room-temperature deformability of the Laves phase TiCr2. The morphology of the Laves phase was found to be dependent upon alloy composition and annealing temperature. Samples deformed by compression have also been studied using TEM. Comparisons of microstructures before and after deformation suggest an increase in twin, stacking faul4 and dislocation density within the Laves phase, indicating some but not extensive room-temperature deformability. Katherine C. Chen Conference Proceedings http://works.bepress.com/kcchen/21 http://works.bepress.com/kcchen/21 Wed, 01 Oct 2008 17:00:27 PDT The effect of composition on the ternary (NbCr2–TiCr2) C15 phase properties has been investigated, focusing upon the defect structure, elastic properties, and mechanical behavior. The C15 phase field is continuous between NbCr2–TiCr2, with a maximum phase field width of at least 7 at.% solubility. The defect mechanism is governed by anti-site constitutional defects for all alloys. Mechanically, the alloys display a maximum in hardness in the center of the ternary phase field (and a minimum of toughness). The ternary phase field has features that are characteristic of solid-solution strengthening mechanisms. Finally, the elastic properties indicate that the alloys become stiffer in the middle of the ternary phase field. The best compromise of properties occurs furthest from stoichiometry in the ternary phase field at the nominal composition of Nb19Ti19Cr62. The relationships between the defect structure, elastic properties, and mechanical response for the C15 phases are discussed using a combination of atomic size arguments and electronic structure analyses. From these relationships, alloy design strategies for NbCr2-based alloys are evaluated. Dan J. Thoma Articles http://works.bepress.com/kcchen/20 http://works.bepress.com/kcchen/20 Wed, 01 Oct 2008 17:00:07 PDT We have developed a laboratory module focusing on the subject of corrosion. The module itself is designed to be completed in one three-hour session. It consists of three parts: I. The Impact of Corrosion Media, II. The Impact of Corroding Materials, III. The Impact of Anode/Cathode Sizes. Our objectives in developing this module were to address the need for clear bridges between math, science and technology in the engineering curriculum and to provide a means of faculty development primarily at community colleges. As a result, it was designed to allow the engineering student to experience the synergy of science, math and engineering technology in a laboratory setting. Recent findings in learning theory research were used in the design of the module to reach students of diverse learning styles. Our targeted audience is sophomore engineering majors at community colleges and institutions without Materials Science and Engineering programs. In this paper we will present the module, its goals, objectives and performance criteria, and the preliminary results of its implementation. Linda Vanasupa Conference Proceedings http://works.bepress.com/kcchen/19 http://works.bepress.com/kcchen/19 Tue, 30 Sep 2008 16:01:20 PDT Near-equiatomic Ni-Ti, known for its shape memory behavior, can decompose to martensitic phases and/or second phase compounds. This phase competition is investigated in NixTi100-x (49<x<55) in as-quenched (AQ) and shock-loaded states. Dynamic loading was done with direct drive laser pulses of nanosecond duration; shocked samples were recovered for analysis. Unexpectedly, the lowest-Ni alloy (x = 48.9) showed reversion of B19’ martensite (present in the AQ state) to the B2 parent phase upon loading, attributed to shock-induced heating. Higher-Ni alloys (x = 50.7, 52.6, 54.5, 54.6) showed Ni4Ti3 but no martensite in the AQ state, consistent with resistivity and dilatometry results which showed no hysteresis indicative of first order phase changes over 1.9 K<T<1273 K. Shock loading these alloys formed no martensite, but the Ni4Ti3 amounts (present in the AQ state) did change upon loading, indicating the importance of shock-induced heating. A thermodynamically complete equation of state (EOS) for NiTi in its B2 (CsCl) structure was generated by ab initio quantum mechanical calculations. This was tested by performing laser-launched flyer experiments, which showed consistency with the theoretical EOS, validating its use in the prediction of dynamic loading histories in the samples during direct drive loading. R. E. Hackenberg Conference Proceedings http://works.bepress.com/kcchen/18 http://works.bepress.com/kcchen/18 Tue, 30 Sep 2008 16:00:58 PDT Solubility limits and constitutional defects in Laves phase intermetallics are investigated with the C15 HfCo2 system. Several binary alloy compositions based on HfCo2 are characterized by optical and scanning electron microscopy (SEM), electron microprobe analysis (EPMA), X-ray diffraction (XRD), and density measurements. Rietveld refinements of XRD scans are used to determine lattice constants, anisotropic strain parameters, and atomic occupancies. Compositional trends are compared against predicted or calculated trends due to an anti-site substitution or vacancy defect mechanism. Geometric models and atomic size factors are used to establish solubility limits and to give insight into defect mechanisms. Results from various, complementary experiments are consistent with anti-site substitutions on both sides of HfCo2 stoichiometry. Katherine C. Chen Articles http://works.bepress.com/kcchen/17 http://works.bepress.com/kcchen/17 Tue, 30 Sep 2008 16:00:45 PDT In efforts to establish and understand structure–property relationships in Laves phase intermetallics, elastic and mechanical properties are studied as a function of composition in the C15 HfCo2 system. Elastic constants and Debye temperatures are determined by resonant ultrasound spectroscopy (RUS) at room temperature. A maximum near the stoichiometric Laves composition is revealed with the Young's modulus, bulk modulus, and Poisson's ratio. In addition, a slight drop in shear modulus is found with Co-rich compositions, and the Debye temperature increases with Co-content. Room temperature Vickers indentation is performed to assess the microhardness and fracture toughness of the HfCo2 alloys. A maximum in hardness occurs near the stoichiometric composition, which is contrary to the behavior displayed in most other classes of intermetallics. Slight improvements in the toughness are found with the Co-rich compositions of the Laves phase. Compositional trends of the properties are attributed to defect structures, and are analyzed with respect to the bonding of the structure and the ease in which the synchroshear deformation process proceeds. Toughening strategies and methodologies are then developed based upon these results. Katherine C. Chen Articles http://works.bepress.com/kcchen/16 http://works.bepress.com/kcchen/16 Tue, 30 Sep 2008 12:44:41 PDT Katherine C. Chen Articles