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Summer 2008 Seminar
Friday, July 11 at 3:30 p.m., Room 184 Watts Hall
Benjamin Peterson
PhD Candidate advised by Dr. Hamish Fraser
Department of Materials Science and Engineering
The Ohio State University
A Combinatorial Approach to the Development of a Creep Resistant Beta Titanium Alloy
Abstract
Timetal 21S has been selected as a baseline for the development of a new high temperature beta titanium alloy. A combinatorial approach employing directed laser deposition of elemental powders has been used to produce a number of test coupons with controlled variations of composition. In addition to the variation of the baseline elements (Ti, Mo, Nb, Al and Si), the alloys contain varying amounts of neutral elements (Zr and Sn), beta-stabilizers (W) and dispersoid formers (B, C and Ge). Subsequently, the creep properties are assessed using an Instron ETMT instrument and represented by their minimum creep rates. The microstructures of the test coupons have been characterized using a range of techniques and have been quantified using rigorous stereological techniques to populate databases and subsequently train and test Bayesian Neural Network models for the prediction of creep properties. Additionally, advanced characterization techniques and computation tools are employed to aid in the identification of the creep rate-limiting microstructural features. For example, SEM and TEM studies show a critical dependence of the size of α-denuded β regions on the creep properties in these β-Ti alloys. The most important microstructural features (volume fraction α, α lath thickness and β mean free path) and alloying additions (Sn and Ge) have been identified and are discussed.
The electrothermal mechanical tester (ETMT), used to investigate creep properties in the work, has also been characterized and compared with traditional tensile and creep testing methods. Computational models incorporating heat transfer and electrostatics were used to investigate the temperature profiles that result from the interaction of joule heating, conductive cooling and radiative cooling in subscale Ti-6Al-4V samples at five current densities in the ETMT. The tensile properties, including YS, UTS, E and total elongation, of sub-scale specimens have been evaluated over a range of temperatures and a variation of microstructural features in α+β and β-processed Ti-6Al-4V using the ETMT and traditional methods. The creep properties for Timetal 21S, α+β and β-processed Ti-6242 are compared with legacy data and traditional means. It was found that the applied direct current increases the minimum creep rate.
Bio
Ben received his B.S. from Arizona State University in Materials Science and Engineering in 2004. He has been working towards his Ph.D. in Materials Science and Engineering under the guidance of Hamish Fraser since the summer of 2004.
