Publications

1997
E. M. Taleff, Syn, C. K., Lesuer, D. R., and Sherby, O. D., “A Comparison of Mechanical Behavior in Pearlitic and Spheroidized Hypereutectoid Steels,” in Thermomechanical Processing and Mechanical Properties of Hypereutectoid Steels and Cast Irons, Warrendale, PA, 1997, pp. 127–142. LinkAbstract
Not available.
K. S. Ball and Taleff, E. M., “Can-in-Canister Alternative for Vitrification of Surplus Weapons Plutonium: Overview of Thermal Issues,” in Nuclear Materials Safety Management, Boston, 1997. LinkAbstract
One option for the long-term disposition of excess weapons plutonium involves vitrification, which entails combining the plutonium with radioactive high-level wastes and glass frit in a melter and then filling small stainless steel “cans” with the molten mixture. Several of these cans are then placed on a “rack” within larger stainless steel canisters, which are subsequently filled with molten high-level waste glass (HLWG) for security against theft. This disposition alternative is referred to as the “Can-in-Canister” option [1]. Of particular concern is the ability of the molten HLWG to flow around the Pu-cans and their support structure to form a proliferation barrier. The canister filling process is investigated experimentally using room temperature model fluids as well as molten HLWG surrogates. Also, analytical results obtained from thermal models and detailed simulations show the role of heat transfer on the temperature distribution within the HLWG, and consequently on the strongly temperature dependent viscosity of the HLWG and its ability to flow and fill the canister.
E. M. Taleff, Lesuer, D. R., Syn, C. K., and Henshall, G. A., “Creep Fracture During Solute-Drag Creep and Superplastic Deformation,” in Recent Advances in Fracture, Warrendale, PA, 1997, pp. 295–306. LinkAbstract
Creep fracture behavior has been studied in Al-Mg and Al-Mg-Mn alloys undergoing solute-drag creep and in microduplex stainless steel undergoing both solute-drag creep and superplastic deformation. Failure in these materials is found to be controlled by two mechanisms, neck formation and cavitation. The mechanism of creep fracture during solute-drag creep in Al-Mg is found to change from necking-controlled fracture to cavitation controlled fracture as Mn content is increased. Binary Al-Mg material fails by neck formation during solute-drag creep, and cavities are formed primarily in the neck region due to high hydrostatic stresses. Ternary alloys of Al-Mg- Mn containing 0.25 and 0.50 wt % Mn exhibit more uniform cavitation, with the 0.50 Mn alloy clearly failing by cavity interlinkage. Failure in the microduplex stainless steel is dominated by neck formation during solute-drag creep deformation but is controlled by cavity growth and interlinkage during superplastic deformation. Cavitation was measured at several strains, and found to increase as an exponential function of strain. An important aspect of cavity growth in the stainless steel is the long latency time before significant cavitation occurs. For a short latency period, cavitation acts to significantly reduce ductility below that allowed by neck growth alone. This effect is most pronounced in materials with a high strain-rate sensitivity, for which neck growth occurs very slowly.
E. M. Taleff, Bramfitt, B. L., Syn, C. K., Lesuer, D. R., and Sherby, O. D., “Mechanical Behavior of an Ultrahigh-Carbon Steel Exhibiting a Damask Surface Pattern,” in Thermomechanical Processing and Mechanical Properties of Hypereutectoid Steels and Cast Irons, Warrendale, PA, 1997, pp. 189–198. LinkAbstract
Not available.
E. M. Taleff and Kim, W. - J., “The Roles of Grain-Boundary Sliding and Dislocation-Pipe Diffusion in High-Strain-Rate Superplasticity,” in Seventh International Conference on Creep and Fracture of Engineering Materials and Structures, Irvine, CA, 1997.Abstract
Not available.
D. R. Lesuer, Nieh, T. G., Syn, C. K., and Taleff, E. M., “Superplastic Deformation in Two Microduplex Stainless Steels,” in International Conference on Superplasticity in Advanced Materials (ICSAM), Bangalore, India, 1997.Abstract
Not available.
K. S. Ball, Song, M., Gomon, M., Silva, M. W., Taleff, E. M., Powers, B. M., and Bergman, T. L., “Canister Filling with a Molten Glass Jet,” ASME Journal of Heat Transfer, vol. 119, pp. 204, 1997. LinkAbstract
Not available.
1996
E. M. Taleff, Nagao, M., Ashida, Y., and Sherby, O. D., “Synthesis of Submicrometer-Grained-Ultrahigh-Carbon Steel Containing 10% Aluminum by Ball Millling of Powders,” Journal of Materials Research, vol. 11, pp. 2725–2730, 1996. LinkAbstract
An ultrahigh-carbon (1.25 wt. %) steel alloy containing 10 wt. % aluminum (UHCS – 10Al) was processed by a powder metallurgy technique. Gas-atomized powders were subjected to ball-milling in an attritor in order to obtain a submicrometer grain size. Powder material was consolidated by both hot isostatic pressing (HIP) and by hot isopressure extrusion (HIE). Bulk material with submicrometer grain sizes was produced from attrited powders. The chemical composition and microstructure of this material are characterized at each processing step, from atomization through consolidation. Tensile tests show that a high strength results from the submicrometer grain size produced in the bulk material.
E. M. Taleff, Nagao, M., Higashi, K., and Sherby, O. D., “High-Strain-Rate Superplasticity in Ultrahigh-Carbon Steel Containing 10 wt.% Al (UHCS-10Al),” Scripta Metallurgica et Materialia, vol. 34, pp. 1919–1923, 1996. LinkAbstract
The present study represents a new processing route by which high-strain-rate superplasticity can be obtained in a two-phase, Fe-base alloy. For this study, an ultrahigh-carbon steel containing 10 wt.% Al (UHCS-10Al) was processed by a powder-metallurgy technique. Mechanical attrition was used to introduce a large degree of cold work into pre-alloyed powders, creating the very fine microstructural features necessary for high-strain-rate superplasticity. Because this material contains two phases, {alpha}-Fe and {kappa}-carbide (Fe{sub 3}AlC{sub x} where x = 0.5 to 1), in the range of processing temperatures, a fine grain size was produced upon consolidation and retained during deformation. It is this fine grain size which is responsible for the high-strain-rate superplastic behavior observed.
E. M. Taleff, Lesuer, D. R., and Wadsworth, J., “Enhanced Ductility in Coarse-Grained Al-Mg Alloys,” Metallurgical and Materials Transactions A, vol. 27A, pp. 343–352, 1996. LinkAbstract
Enhanced ductilities,i.e., values of tensile ductility exceeding those normally expected in metallic alloys, have been observed at warm temperatures in coarse-grained Al-Mg alloys which exhibit viscous-glide controlled creep. Numerous tests have been conducted in order to quantify this phe-nomenon over wide ranges of temperature and magnesium concentration. The contributions of strain-rate sensitivity and strain hardening have been analyzed in relation to the observed tensile ductilities. It is shown that an analysis based only on flow instability in tension cannot be used to predict failure in a unique manner.
E. M. Taleff, Syn, C. K., Lesuer, D. R., and Sherby, O. D., “Pearlite in Ultrahigh Carbon Steels: Heat Treatments and Mechanical Properties,” Metallurgical and Materials Transactions A, vol. 27A, pp. 111-118, 1996. LinkAbstract
Two ultrahigh carbon steel (UHCS) alloys containing 1.5 and 1.8 wt pct carbon, respectively, were studied. These materials were processed into fully spheroidized microstructures and were then given heat treatments to form pearlite. The mechanical properties of the heat-treated materials were evaluated by tension tests at room temperature. Use of the hypereutectoid austenite-cementite to pearlite transformation enabled achievement of pearlitic microstructures with various interlamellar spacings. The yield strengths of the pearlitic steels are found to correlate with a predictive relation based on interlamellar spacing and pearlite colony size. Decreasing the pearlite interlamellar spacing increases the yield strength and the ultimate strength and decreases the tensile ductility. It is shown that solid solution alloying strongly influences the strength of pearlitic steels.
1995
E. M. Taleff, Henshall, G. A., Lesuer, D. R., Nieh, T. G., and Wadsworth, J., “Enhanced Ductility of Coarse-Grain Al-Mg Alloys,” in Superplasticity and Superplastic Forming, 1995, pp. 3–10. LinkAbstract
Enhanced ductilities,i.e., values of tensile ductility exceeding those normally expected in metallic alloys, have been observed at warm temperatures in coarse-grained Al-Mg alloys which exhibit viscous-glide controlled creep. Numerous tests have been conducted in order to quantify this phe-nomenon over wide ranges of temperature and magnesium concentration. The contributions of strain-rate sensitivity and strain hardening have been analyzed in relation to the observed tensile ductilities. It is shown that an analysis based only on flow instability in tension cannot be used to predict failure in a unique manner.
E. M. Taleff, Henshall, G. A., Lesuer, D. R., Nieh, T. G., and Wadsworth, J., “Enhanced Tensile Ductility in Al-Mg Alloys by Solid-Solution Interactions,” in Aluminum and Magnesium for Automotive Applications, Warrendale, PA, 1995, pp. 125–134. LinkAbstract
The development of methods for obtaining high tensile elongation in aluminum alloys is of great importance for the practical forming of near-net-shape parts. Current superplastic alloys are limited in use by high material costs. The utilization of solute-drag creep processes, the approach used in this study, to obtain enhanced tensile ductility in aluminum alloys has lead to tensile elongations of up to 325% in simple, binary Al-Mg alloys with coarse grain sizes. This method has the advantage of lowering processing costs in comparison with superplastic alloys because a fine grain size is not necessary. Whereas superplastic alloys typically have a strain-rate sensitivity of m = 0.5, the enhanced ductility Al-Mg alloys typically exhibit m = 0.3 where maximum ductility is observed. Although a strain-rate sensitivity of rn = 0.5 can lead to elongations of over 1000% (superplastic materials) a value of m = 0.3 is shown experimentally to be sufficient for obtaining elongations of 150% to a maximum observed of 325%. Enhanced ductility is also affected strongly by ternary alloying additions, such as Mn, for which a preliminary understanding is pursued.
J. Wadsworth, Henshall, G. A., Nieh, T. G., and Taleff, E. M., “Materials Issues in Some Advanced Forming Techniques, Including Superplasticity,” in Emerging Technologies, 1995, pp. 87–94. LinkAbstract
From mechanics and macroscopic viewpoints, the sensitivity of the flow stress of a material to the strain rate, i.e. the strain rate sensitivity (m), governs the development of neck formation and therefore has a strong influence on the tensile ductility and hence formability of materials. Values of strain rate sensitivity range from unity, for the case of Newtonian viscous materials, to less than 0.1 for some dispersion strengthened alloys. Intermediate values of m = 0.5 are associated with classical superplastic materials which contain very fine grain sizes following specialized processing. An overview is given of the influence of strain rate sensitivity on tensile ductility and of the various materials groups that can exhibit high values of strain rate sensitivity. Recent examples of enhanced formability (or extended tensile ductility) in specific regimes between m = 1 and m = 0.3 are described, and potential areas for commercial exploitation are noted. These examples include: internal stress superplasticity, superplastic ceramics, superplastic intermetallics, superplastic laminated composites, superplastic behavior over six orders of magnitude of strain rate in a range of aluminum-based alloys and composites, and enhanced ductility in Al-Mg alloys that require no special processing for microstructural development.
W. - J. Kim, Taleff, E. M., and Sherby, O. D., “A Proposed Deformation Mechanism for High Strain-Rate Superplasticity,” Scripta Metallurgica et Materialia, vol. 32, pp. 1625–1630, 1995. LinkAbstract
Superplasticity at high deformation rates is desirable in order to make superplastic forming more practical. Recently, superplasticity was achieved at strain rates between 10{sup {minus}2} and 100 s{sup {minus}1} in powder-metallurgy (PM) processed and mechanically alloyed (MA) aluminum alloys. The purpose of this paper is to understand the rate-controlling-deformation mechanisms for ultrafine-grained aluminum materials where high-strain-rate superplasticity is observed. The stress-strain rate relations for IM, PM and MA materials are analyzed in terms of deformation mechanism maps, and in terms of the contribution of subgrain boundaries to the enhancement of grain boundary sliding. Conclusions are as follows: (1) Lattice-diffusion-controlled grain boundary sliding is believed to be the rate-controlling mechanisms for high-strain-rate superplasticity in PM and MA aluminum alloys. (2) Construction of deformation mechanisms maps based on diffusional creep, grain boundary sliding and dislocation creep illustrate the importance of grain size in achieving high-strain- rate-superplasticity. (3) The Ball-Hutchinson model for grain-boundary sliding has been modified to include the influence of subgrain size in enhancing the grain boundary sliding process. (4) The introduction of threshold stress for grain boundary sliding and the important contribution of grain and subgrains permit unification of all superplastic IM, PM and MA aluminum data available.
1994
E. M. Taleff, Henshall, G. A., Lesuer, D. R., and Nieh, T. G., “Warm Formability of Aluminum-Magnesium Alloys,” in Aluminum Alloys: Their Physical Properties and Mechanical Properties (ICAA4), Atlanta, Georgia: Georgia Institute of Technology, 1994, pp. 338–345.Abstract
Not available.
E. M. Taleff and Sherby, O. D., “Mechanical Behavior of Fine-Grained Mg-6.5Li at Elevated Temperature,” Journal of Materials Research, vol. 9, pp. 1392–1396, 1994. LinkAbstract
Only available as a scanned document. See link.
E. M. Taleff, “Superplasticity at High Strain-Rates in Fine-Grain Ultrahigh-Carbon Steel,” Stanford University, 1994.Abstract
Not available online, Ph.D. thesis.
1992
E. M. Taleff, Ruano, O. A., Wolfenstine, J., and Sherby, O. D., “Superplastic Behavior of a Fine-Grained Mg-9Li Material at Low Homologous Temperature,” Journal of Materials Research, vol. 7, pp. 2131–2135, 1992. LinkAbstract
No abstract available. Only available as a scanned document.

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