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Determination of Activation Energies and Modeling of Low Temperature Creep of Alpha, Alpha-Beta, and Beta Titanium Alloys Sreeramamurthy Ankem, Universiity of Maryland College Park, DMR 0513751. INTELLECTUAL MERIT.

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  1. Determination of Activation Energies and Modeling of Low Temperature Creep of Alpha, Alpha-Beta, and Beta Titanium AlloysSreeramamurthy Ankem, Universiity of Maryland College Park, DMR 0513751 INTELLECTUAL MERIT OVERVIEW Titanium alloys have many applications including aerospace, naval, biomedical, and nuclear. Often, titanium components are subject to loading for long periods of time at low temperatures. Titanium has long been known to creep, i.e.: time-dependent permanent deformation, at low temperatures. Therefore, it is important to understand the mechanisms of creep deformation to predict the mechanical reliability of the structures and to design advanced materials with improved creep resistance. APPROACH Mechanical Testing, TEM & SEM Microscopy, Crystallographic Modeling, and Modeling of deformation mechanisms based on thermodynamics and kinetics principles. TEM micrographs of twins from creep deformed α-Ti–1.6wt.% V at (a) 25°C, (b) 85°C, and (c) 205°C. RESULTS The effect of time-dependent twinning on low temperature (<0.25 * Tm) creep of an alpha-titanium alloy was analyzed. This analysis showed that time dependent twinning is an important deformation mechanism in the temperature range 25-205°C, at the later stages of creep deformation. This conclusion is based on the activation energies, which were found to increase with increasing creep strain. The initial low activation energies are consistent with primarily slip controlled deformation at the beginning and followed by both slip and time dependent deformation at later stages.

  2. Determination of Activation Energies and Modeling of Low Temperature Creep of Alpha, Alpha-Beta, and Beta Titanium AlloysSreeramamurthy Ankem, Universiity of Maryland College Park, DMR 0513751 BROADER IMPACTS EDUCATION One graduate student, Mr. Zane Wyatt, and one undergraduate student, Mr. Ryan Mulholland, were involved with research under this grant. • OUTREACH The outcomes of the research are being communicated to the professionals in the field and to the general public in the form of presentations and publications. Presentations and Publications in 2008 include: • “The Role of Deformation Twinning on Creep of Titanium Alloys”, S. Ankem and P.G. Oberson, Presented at “The 6th Pacific Rim International Conference on Advanced Materials and Processing”, November 5-9, 2007, Jeiu Island, Korea. • Invited Keynote Presentation “Recent Advances in Twinning”, S. Ankem and P.G. Oberson, Presented at the “International Symposium on Plasticity”, January 3-8, 2008, Kona, Hawaii. • 2008 TMS Annual Meeting, March, 2008, “The Role of Interstitials on Slow Twin Growth in Alpha and Beta Titanium.” P.G. Oberson and S. Ankem. • “The Role of Deformation Twinning on Creep of Titanium Alloys”, S. Ankem and P.G. Oberson, Materials Science Forum, Vols. 561-565, 2007, 121-126. • “The effect of time-dependent twinning on low temperature (<0.25 * Tm) creep of an alpha-titanium alloy”, P.G. Oberson and S. Ankem, Accepted for publication June 2008 in International Journal of Plasticity.

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