Download or read book Dynamic Abnormal Grain Growth in Selected Refractory Metals written by Nicholas Alan Pedrazas and published by . This book was released on 2013 with total page 636 pages. Available in PDF, EPUB and Kindle. Book excerpt: Dynamic abnormal grain growth (DAGG) is a phenomenon by which single crystals up to centimeters in length are produced at elevated temperature during the application of strain. DAGG was previously demonstrated in commercial-purity molybdenum (Mo) materials. This is the first investigation to confirm DAGG in another material, tantalum (Ta). Previous experiments initiated and propagated DAGG using constant true-strain rate tensile tests, but this study demonstrates that DAGG can also occur under constant true-stress tensile conditions. A Mo material was tested under constant true stress, and two Ta materials were tested under constant true-strain rate. The effects of temperature, stress, strain rate, initial microstructure and texture on tensile test data and the resulting microstructures are examined. The microstructures of the Ta materials are analyzed using electron backscatter diffraction (EBSD) data to quantify the orientation, deformation, grain boundary character, and slip properties of the DAGG grains and unconsumed microstructure. The DAGG grains were found to be relatively undeformed compared to the unconsumed microstructure following DAGG and to not be oriented favorably, or unfavorably, for slip. The grain boundaries between DAGG grains in one Ta material were found to commonly have [sigma]3 character. This was likely due to a strong initial 111-fiber texture. Previous investigations of DAGG in Mo indicated that DAGG grains commonly grow along the surface of the specimen, but this was not observed with significant frequency in Ta. Results suggest that the distance the DAGG grain boundary travels is proportional to the accumulated strain during DAGG, and the velocity of the DAGG grain boundary is proportional to the applied strain rate but is not related to the orientation of the DAGG grain or its slip properties.

Download or read book The Influence of High temperature Tensile Deformation on Microstructure Evolution in Select BCC Metals written by Philip James Noell and published by . This book was released on 2015 with total page 356 pages. Available in PDF, EPUB and Kindle. Book excerpt: High-temperature plastic deformation can enhance the rate of grain boundary migration in some metals. In the body-centered-cubic (BCC) refractory metals molybdenum and tantalum, this increased rate of grain boundary migration produces abnormal grain growth at temperatures significantly lower than is possible by static annealing. This phenomenon is termed dynamic abnormal grain growth (DAGG). The influence of microstructure on DAGG is studied by examining the morphology of DAGG grains produced in two Mo sheet materials. DAGG grain propagation in these materials is not uniform throughout the sheet thickness. Variations through the sheet thickness in texture and grain size are explored as causes of these behaviors. DAGG grains in both materials preferentially grow into the finest-grained polycrystalline regions of the sheet. Direct effects of local crystallographic texture variation are not evident in microstructures containing DAGG grains. The initiation of abnormal grains in Mo materials by plastic straining at elevated temperatures is investigated. The minimum strain necessary to initiate DAGG, termed the critical strain, decreases approximately linearly with increasing temperature. The variation in critical strain values observed at a single temperature and strain rate is well described by a normal distribution. An increased fraction of grains aligned with the 110 along the tensile axis, a preferred orientation for DAGG grains, appears to decrease the critical strain for DAGG initiation. Uniaxial tension tests at temperatures between 1650 and 1950 °C were conducted with commercial-purity Mo rods to determine if DAGG can be used to produce large single crystals of Mo. Necking in these tensile rod specimens during the production of DAGG grains presents a potential issue with translation to commercial application. High-temperature tensile tests were also performed on another BCC metal, an interstitial-free steel. Grain growth in this interstitial-free steel during high-temperature plastic deformation is significantly accelerated above that of the static case. Grains generally oriented between {112}110 and {111}113 grow more readily than other grains during dynamic grain growth in this material.

Download or read book The Effect of Fabrication History and Microstructure on the Mechanical Properties of Refractory Metals and Alloys written by Albert G. Imgram and published by . This book was released on 1963 with total page 80 pages. Available in PDF, EPUB and Kindle. Book excerpt: This report summarizes the present knowledge concerning the relationship among fabrication history, metallurgical structure, and the mechanical properites of the refractory metals columbium, tantalum, bolybdenum, and tungsten, and their alloys. These are the refractory metals currently reveiveing the most attention for aerospace applications, and are therefore the materials considered in this survey. The report is organized into three main sections, titled ''Fabrication'', ''Microstructure and Alloying'', and ''Interstitial Impurities''. The data presented were selected as those which best illustrate the topics discussed. Descriptions of the metaljurgical principles involved are included. Suggestions for optimizing mechanical properties by controlling metallurgical structure are made where possible. (Author).

Download or read book Abnormal grain growth in metals written by James Dennis and published by . This book was released on 2008 with total page 290 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Properties of Refractory Metals written by Walter D. Wilkinson and published by . This book was released on 1969 with total page 380 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Refractory Metals and Alloys IV written by Robert Isaac Jaffee and published by . This book was released on 1969 with total page 802 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Recrystallization and Grain Growth in Metals written by P. Cotterill and published by John Wiley & Sons. This book was released on 1976 with total page 424 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Monte Carlo Potts Investigation of the Role of Sparse Recrystallization in Dynamic Abnormal Grain Growth written by Alan Scott Williamson and published by . This book was released on 2015 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: Dynamic Abnormal Grain Growth (DAGG) is a type of abnormal grain growth discovered in Molybdenum that occurs during dynamic straining at medium homologous temperatures. Specifics about DAGG initiation and propagation are dependent on the processing conditions experienced by the material. The mechanism responsible for DAGG has yet to be identified. Proposed is a theory is for explaining DAGG, through the nucleation and growth of a sparse number of recrystallized grains DAGG is achieved. These recrystallized grains could grow abnormally using their strain energy driving force advantage. This theory is investigated numerically by modeling dynamic recrystallization using the Monte Carlo Potts method. Dynamic recrystallization is modeled using a combination of dynamic straining, nucleation of recrystallized grains and grain growth. Dynamic recrystallization is studied to answer whether sparse recrystallization is possible, if sparse recrystallization can cause abnormal grain growth and under what conditions sparse recrystallization is accomplished. Viable sparse recrystallization can be achieved and will cause DAGG-like behavior through the nucleation and rapid growth of a single recrystallized grain. The conditions to achieve sparse recrystallization are examined using the relationship recrystallization has with strain energy and microstructure parameters. Results show that a critical strain energy is needed to allow viable nucleation of recrystallized grains. The value of the critical strain energy is the equivalent of 6 grain boundary segments of non-dimensional (n.d.) energy. The inclusion of external solid-vapor surfaces can reduce the critical strain energy to 5 n.d. Strain energy also directly influences the rate of nucleation. By minimizing strain energy, while keeping it is above the critical value, nucleation can be suppressed enough to allow sparse recrystallization. The microstructure will also influence recrystallization. The grain size of the microstructure is found to behave inversely to the strain energy, where large grain sizes promote sparse recrystallization. Large grain sizes reduce the availability of nucleation sites and the creation of new nucleation sites. Non-ideal microstructural features can reduce the availability of nucleation sites when anisotropic grain boundary energy, or nano-sized pinning particles are incorporated.

Download or read book An Investigation of Abnormal Grain Growth in High Speed Steel written by Andreas Andersen and published by . This book was released on 1951 with total page 28 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Scientific and Technical Aerospace Reports written by and published by . This book was released on 1987 with total page 1124 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Metals Abstracts written by and published by . This book was released on 1996 with total page 732 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Chemical Abstracts written by and published by . This book was released on 2002 with total page 2726 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Nuclear Science Abstracts written by and published by . This book was released on 1974 with total page 1014 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book ASM Handbook written by ASM International. Handbook Committee and published by ASM International(OH). This book was released on 2000 with total page 1242 pages. Available in PDF, EPUB and Kindle. Book excerpt: This index eliminates that need to search through multiple back-of-the-book indexes to find where a subject is addressed. The A-to-Z listing will help users find important handbook content in volumes where they may not have thought to look.

Download or read book Rapidly Quenched Metals III written by B. Cantor and published by . This book was released on 1978 with total page 504 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Metals Abstracts Index written by and published by . This book was released on 1995 with total page 1596 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Handbook of Nanoscience Engineering and Technology written by William A. Goddard III and published by CRC Press. This book was released on 2002-10-29 with total page 830 pages. Available in PDF, EPUB and Kindle. Book excerpt: Nanotechnology, science, and engineering spearhead the 21st century revolution that is leading to fundamental breakthroughs in the way materials, devices, and systems are understood, designed, made, and used. With contributions from a host of world-class experts and pioneers in the field, this handbook sets forth the fundamentals of nanoelectromechanical systems (NEMS), studies their fabrication, and explores some of their most promising applications. It provides comprehensive information and references for nanoscale structures, devices, and systems, molecular technology and nanoelectromechanical theory, and promises to become a standard reference for the field.