Ultrafine-Grained TiAl-Based Alloys for High Temperature Applications

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TECHICAL SUMMARY:The extensive research in nanocrystalline and ultrafine-grained materials has revealed that they have impressive combination of strength and ductility in the absence of processing defects. However, the thermal stability and high temperature creep resistance of these materials in single phase form are unfavorable. In this work, a new and innovative approach in which these properties can be enhanced by creating a high melting point microstructure consisting of ultrafine grains decorated with nanosize ultra-hard and stable particles is proposed. The objective of this research is to intelligently design ultrahigh temperature light alloys based on the Ti-Al-Nb-Cr-X (X = Mo, B) system for applications in engines used in aviation. The combined room temperature toughness and high temperature strength will be achieved by creating a microstructure consisting of ultrafine-grained -TiAl phase with nano-size -Nb2Al particles distributed effectively and at grain boundaries. The -TiAl phase is not ductile at room temperature for several reasons, including localized deformation owing to the lack of activation of enough slip systems. Refining the grain size and alloying are anticipated to homogenize plastic deformation and reduce the probability of fracture of the phase through modifying the local stress state and affecting intrinsic parameters such as bonding. The presence of the nanocrystals of the ultra-hard sigma phase combined with the additions of refractory metals will allow achieving high temperature phase stability and creep resistance. State-of-the-art computational techniques and intelligent, sophisticated and advanced experimental methods will be employed to reach the goals of the proposed work.NON-TECHNICAL SUMMARY:The scarcity of fossil fuels and the increase in air travel frequency owing to the demands of industrial globalization require economically feasible high-performance aircraft. The performance of gas turbine engines can be improved by increasing the gas temperature and decreasing the weight of the engine. Material limitations are among the road blocks to building engines with higher performance levels. The results of this research will impact the society with the prospect of creating a new family of high temperature metallic materials. The education activities will include both graduate and undergraduate students. A diverse group of students will be involved in this project, including one minority and one female graduate student. Emphasis will be placed on the involvement of undergraduate students in research. The undergraduate students will be involved through two different programs, namely Research Experience in Materials, a new program at the Materials Science and Engineering (MSE) Department at the University of Florida, and the required Undergraduate Senior Thesis course in the MSE department.