CAREER: Understanding the Role of Nanoprecipitates in Advanced Metastable Titanium Alloys

在材料科学中，强度是衡量材料承受载荷或承载重量而不失效的能力。另外，延展性是衡量材料弯曲、拉伸或扩散而不碎成碎片的能力。通常，材料强度的增加会导致延展性的降低，反之亦然。该项目支持钛合金设计的基础研究，通过精心定制合金的元素组成来克服这种典型的强度与延展性之间的权衡。这种精心的剪裁控制着金属的特定部分如何在原子水平上排列，以具有特定的化学成分和排列，从而增加材料的强度，同时又不降低材料的整体弯曲或拉伸能力。这种类型的设计被称为亚稳态工程。本项目研究具有相同元素组成和原子结构的钛合金零件如何随着温度和化学成分的变化而变化，以及它们如何在各种情况下变形。为了探索这种行为，使用尖端设备进行实时和“事后”研究，以发现局部化学，不同环境和金属中纳米尺寸的非常小的颗粒之间的联系，这些颗粒最近才在钛中发现。在这个项目中建立的基础知识提高了设计轻质钛合金的能力，同时具有高强度和高延展性。亚稳态钛合金由于其高强度重量比、吸收冲击的能力、耐化学变质和与生物应用的兼容性，是航空航天、汽车、生物医学和化学工业的理想选择。例如，相对于这些行业中的一个，这些合金的改进可以帮助提高飞机的燃油效率，减少燃料消耗，降低碳排放，最终有利于环境。该项目还为K-12夏令营的学生开发教育模块，并为内华达大学里诺分校的本科生和研究生开发实验室体验。这两组活动都以高倍显微镜为特色，为里诺当地社区的学生提供了接触科学和技术的机会，同时也为妇女和代表性不足的少数民族提供了学习材料科学的机会，以培养未来的科学人才。本项目旨在通过研究亚稳钛合金的微观组织演变和变形，提出一种称为亚稳工程的新型合金设计策略。该项目将确定最近发现的正交纳米沉淀O ' （O '）在钛及其合金的空间受限相变中的关键作用。采用先进的非原位和原位表征技术，研究了三种具体现象：(i)合金成分与O '纳米析出物之间的关系；（ii） O′在细化析出相组织中的作用；(3) O′在调节马氏体相变中的作用。使用扫描电子显微镜、透射电子显微镜、扫描透射电子显微镜和原子探针层析成像进行多尺度原位和原位实验表征。本研究为实现高强度、高延展性的钛亚稳态合金提供了可能。教育模块和推广活动的重点是电子显微镜创造性地吸引学生K-12，本科和研究生水平的学习。教育模块和活动通过遥控透射电子显微镜和便携式桌面扫描电子显微镜来增强，以捕捉广泛的兴趣，并使所有人都接触到有意义的科学。这些教育活动为邻近社区的学生提供了前所未有的实时科学知识，并为内华达大学里诺分校的学生提供了一种实用的方法，通过接触他们所在机构的高级特性，提高他们的课堂教学水平。所有的活动都有助于培养未来的STEM劳动力，培养各年龄段学生对材料科学的兴趣。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

NON-TECHNICAL SUMMARYIn materials science, strength is the measure of a material’s ability to bear a load or carry weight without failing. Alternatively, ductility is a measure of a material’s ability to bend, stretch or spread without breaking into pieces. Often, increasing the strength of a material results in a decrease of ductility and vice versa. This project supports fundamental research focused on the design of Titanium alloys that overcome this typical strength-to-ductility trade-off by carefully tailoring the elemental make-up of said alloys. This careful tailoring controls how specific parts of the metal are arranged on an atomic level to have a certain chemical composition and arrangement that increases the material’s strength without reducing the material’s overall ability to bend or stretch. This type of design is known as metastability engineering. This project investigates how parts of Titanium alloys having the same elemental makeup and atomic structure change with both temperature and chemical composition and how they deform under various circumstances. To explore this behavior, real-time and “after the fact” studies are performed using cutting edge equipment to discover connections between local chemistry, different environments and very small particles in the metal that are nanometers in size and have only recently been discovered in Titanium. The fundamental knowledge established in this project advances the ability to design lightweight Titanium alloys with both high strength and high ductility. Metastable titanium alloys are desirable for aerospace, automobile, bio-medical and chemical industries, due to their high strength-to-weight ratio, ability to absorb impact, resistance to chemical deterioration and compatibility with biological applications. As an example, relative to just one of these industries, improvements to these alloys can help to increase aircraft fuel efficiency, reduce fuel consumption, lower carbon emissions and ultimately, benefit the environment. This project also develops education modules for students in a K-12 Summer Camp as well as lab experiences for undergraduate and graduate students at the University of Nevada Reno. Both sets of activities feature high powered microscopes providing students from local Reno communities exposure to science and technology while also providing opportunities for women and underrepresented minorities to learn materials science for the purpose of developing the future scientific workforce.TECHNICAL SUMMARYThis project aims to advance a novel alloy designing strategy known as metastability engineering, by studying microstructural evolution and deformation in metastable Titanium alloys. The project will identify the critical role of the recently discovered, orthorhombic nano-precipitate, O prime (O’) in the spatially confined phase transformations of Titanium and its alloys. Advanced ex-situ and in-situ characterization techniques are employed to explore three specific phenomena: (i) The relationship between alloy composition and O’ nano-precipitates; (ii) The role of O’ in refining precipitate microstructure; and (iii) the role of O’ in regulating martensitic transformations. Multiscale ex- and in-situ experimental characterization using scanning electron microscopy, transmission electron microscopy, scanning transmission electron microscopy and atom probe tomography are used. This research progresses the ability to realize metastable alloys of Titanium having both high strength and high ductility. Education modules and outreach activities focused on electron microscopy creatively engage students in K-12, undergraduate and graduate level study. The education modules and activities are enhanced by a remote-controlled transmission electron microscope and a portable desktop scanning electron microscope to capture a wide range of interests and expose all to meaningful science. These education activities provide students in the neighboring community unprecedented access to science in real-time and offers to the student body at the University of Nevada, Reno a practical means of enhancing their in-class instruction with exposure to advanced characterization being performed at their institution. All activities assist with developing a future STEM workforce by generating interest in materials science to students at all ages.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.