Dynamic Abnormal Grain Growth and the Production of Single Crystals

1. DAGG is plastic strain dependent DAGG start end single crystal bicrystal Powder-metallurgy Mo specimens from several experiments are shown. Ductile recrystallized Mo demonstrated Mo polycrystal Crystal growth Polycrystal Mo polycrystal Single Crystal Tensile Direction Polycrystal Polycrystal DAGG Front Mo single crystal Mo single crystal Room-temperature bends Dynamic Abnormal Grain Growth and the Production of Single Crystals Eric M. Taleff, University of Texas at Austin, DMR 0605731 • Dynamic Abnormal Grain Growth (DAGG), which occurs by the application of critical plastic strain at elevated temperatures, is applied to a new material synthesis process for the production of large single crystals in the solid state. • Key Points: • Large single crystals, bicrystals and tricrystals have been grown in Mo by DAGG at 1540°C (0.63Tm) and higher temperatures. • The DAGG front is driven by plastic straining, which provides a means for controlling growth. • Advantages over static abnormal grain growth techniques, such as strain annealing, include dramatically lower temperature and the elimination of island grains. • Mo single crystals demonstrate room-temperature ductility not possible in recrystallized polycrystals. • DAGG has the potential to produce large single crystals in materials which undergo polymorphic transformations. • Collaborations: • Dan Thoma at Los Alamos National Laboratory: pursuing follow-on research into DAGG in uranium. • Participants: • Dr. James Ciulik (Post-doctoral fellow and co-inventor) • Jung-Kuei “Brian” Chang and Daniel Worthington (Graduate research assistant) • Andrea Pearlman, Nicholas Pedrazas, Christine Tower and Melissa Diekroeger (Undergraduate research assistants)

2. Dynamic Abnormal Grain Growth and the Production of Single Crystals Eric M. Taleff, University of Texas at Austin, DMR 0605731 • Broader Impacts • Research: • Large single crystals, bicrystals and tricrystals have been grown in Mo sheet by DAGG at 1540°C (0.63Tm) and higher temperatures. • The creep behavior of commercial-purity tungsten was characterized in the temperature range of 1500 to 1800°C (0.48to 0.56Tm). • Although DAGG was not observed during testing, it is anticipated that testing at higher temperatures may result in DAGG. • Our DAGG method has recently been used to produce large-grained uranium at Los Alamos National Laboratories. • Our DAGG method has recently been used to produce large-grained, high-purity iron specimens at UC Davis. • Education: • Two graduate students are involved in research under this grant. • Jung-Kuei “Brian” Chang is completing a doctoral degree and has observed abnormal grain growth in Al-Mg alloys. • Daniel Worthington is working toward a doctoral degree and has produced large-grained uranium at Los Alamos National Laboratories. • Four undergraduate students were involved in research under this grant. • Andrea Pearlman completed a bachelor's degree and conducted creep testing of tungsten in the temperature range of 1500 to 1800°C. • Nicholas Pedrazas is working toward a bachelor's degree and produced DAGG in molybdenum sheet at 1640°C and 1740°C and constructed a fixture to allow creep testing of Mo and W wire. • Melissa Diekroeger is working toward a bachelor's degree and constructed instrumentation to investigate solid-state crystal growth. • Christine Tower completed a bachelor's degree and produced a review of materials literature. • One post-doctoral fellow is involved in research under this grant. • Dr. James Ciulik is studying the growth of molybdenum single crystals in sheet and wire and is undertaking experiments to determine if DAGG can be produced in tungsten. • Outreach: • Research results have been presented at national conferences: • 1. Ciulik, J., and E. M. Taleff, "Dynamic Abnormal Grain Growth in Commercial-Purity Molybdenum," Proceedings of the 2006 International Conference on Tungsten, Refractory & Hardmetals VI, Orlando, FL, February 2006 • 2. Ciulik, J., and E. M. Taleff, “Effects of Microstructure on Creep Properties of Commercial-Purity Molybdenum," TMS 2006 Annual Meeting, March 12-16, 2006, San Antonio, TX • Research results have been published in peer-reviewed journals: • 1. J. Ciulik and E.M. Taleff, “Power-Law Creep of Powder-Metallurgy Grade Molybdenum Sheet,” Materials Science and Engineering A, Volume 463, Issues 1-2, p197-202 (2007)