Ultrafine-Grained TiAl-Based Alloys for High Temperature Applications

摘要：对纳米晶和超细晶材料的广泛研究表明，它们在没有加工缺陷的情况下具有令人印象深刻的强度和延展性。然而，这些材料在单相形式下的热稳定性和高温抗蠕变性是不利的。在这项工作中，提出了一种新的和创新的方法，其中这些性能可以通过创建一个高熔点的微观结构，由超细晶粒装饰纳米尺寸的超硬和稳定的颗粒来增强。本研究的目的是智能化设计Ti-Al-Nb-Cr-X（X = Mo，B）系中温轻合金用于航空发动机。结合室温韧性和高温强度将通过创建由超细晶粒的#61543;-TiAl相与纳米尺寸的#61555;-Nb 2Al颗粒有效地分布和在晶界处组成的显微组织来实现。#61543&;-TiAl相在室温下是不延展的，原因有几个，包括由于缺乏足够的滑移系统的活化而导致的局部变形。预期细化晶粒尺寸和合金化可使塑性变形均匀化，并通过改变局部应力状态和影响内在参数（例如结合）来降低#61543;#61472;相的断裂概率。超硬σ相的纳米晶体的存在与难熔金属的添加组合将允许实现高温相稳定性和抗蠕变性。国家的最先进的计算技术和智能，复杂和先进的实验方法将被用来达到拟议的工作的目标。非技术摘要：化石燃料的稀缺和航空旅行频率的增加，由于工业全球化的需求，需要经济上可行的高性能飞机。燃气涡轮机的性能可以通过提高燃气温度和减轻发动机重量来改善。材料限制是制造更高性能发动机的障碍之一。本研究成果将对社会产生影响，具有创造新的高温金属材料家族的前景。教育活动将包括研究生和本科生。一个不同的学生群体将参与这个项目，包括一个少数民族和一个女研究生。重点将放在本科生参与研究。本科生将通过两个不同的程序，即材料研究经验，在材料科学与工程（MSE）部门在佛罗里达大学的一个新的程序，并在MSE部门所需的本科高级论文课程参与。

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.