Fundamental Mechanisms in Stress-Aided Variant Selection of Nanoscale Precipitation

非技术性SUMMARY镍基高温合金在高温下使用时具有高强度和耐腐蚀性。由于这些重要的特性，它们已被广泛应用于高性能内燃机，如燃气轮机、热电厂和核电站。为了在高温下获得优异的力学性能，沉淀强化技术被广泛应用于高温合金的强化。该计划将侧重于了解和控制镍基高温合金中析出物相对于合金母体的取向，即变体选择。还将研究在应力辅助时效过程中所选择的变量对力学性能的调制。从该计划中获得的见解将促进对强化机制的理解，并为相关行业提供新的指导，以提高合金的机械性能。该计划不仅将促进科学进步，而且由于对航空航天、热力和核工业的贡献，还将促进国家的繁荣和福利，在这些行业，高温燃气轮机组件的性能增强可以显著提高飞机发动机和发电厂的效率。此外，该奖项将鼓励工程领域的妇女和代表性不足的群体，并通过创造性的学习模块和研讨会等大学项目加强社区和外联活动。金属材料的力学性能与其内部组织密切相关。特别是，析出粒子的形态，包括它们的形状、取向和分布，对相分离合金的性能起着至关重要的作用。变型选择是指相对于合金基质形成特定的析出物取向。以镍基合金为例，研究了在形核和生长早期选择不同的共格纳米析出物的形成机制以及相应的调制力学性能。我们的目标是回答以下基本问题：-如何通过改变重要材料和工艺参数来控制变体选择的启动；-如何通过选择理想滑移系统处于优先方向的变体来实现各向异性强化？这项技术工作的特点是采用紧密结合的计算和实验方法来(1)阐明材料参数在形核和形变早期阶段的影响，(2)制备单晶样品，(3)研究拉伸和蠕变变形过程中的各向异性强化。由于镍基合金的广泛应用，该计划将重点放在镍基合金上。然而，阐明的基本机制适用于大多数含有一致沉淀的合金，例如新型耐火合金。该奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

NON-TECHNICAL SUMMARYNickel-based superalloys possess combined high strength and corrosion resistance during service at elevated temperatures. Due to these important characteristics, they have been widely used in high-performance combustion engines, such as gas turbines, thermal and nuclear power plants. In order to achieve superior mechanical properties at high temperatures, precipitation hardening has been widely employed to strengthen superalloys. This program will focus on understanding and controlling the orientation of precipitates with respect to the alloy matrix, i.e., variant selection, in a nickel-based superalloy. The modulated mechanical properties by selected variant during the stress-assisted aging process will be also investigated. Insights gained from the program will advance the understanding of strengthening mechanisms as well as provide related industries with new guidance to improve the mechanical properties of alloys. The program will not only promote the progress of science but will also advance the national prosperity, and welfare due to the contribution to the aerospace, thermal and nuclear industry, where the enhanced performance of high temperature gas turbine components can significantly increase the efficiency of aircraft engines and power plants. In addition, this award will encourage women and underrepresented groups in engineering and enhance community and outreach activities through creative learning modules and workshops among other university programs. TECHNICAL SUMMARYThe mechanical properties of metallic materials are closely related to their internal microstructure. In particular, the morphology of precipitate particles including their shape, orientation and distribution can critically determine the properties of phase-separated alloys. Variant selection refers to the formation of a particular precipitate orientation with respect to the alloy matrix. Using Ni-based alloys as an example, the formation mechanisms of variant selection of coherent nanometer-sized precipitates at the nucleation and early growth stage, and the corresponding modulated mechanical properties will be investigated. We aim to answer the following fundamental questions: -How can one control the initiation of variant selection through varying important materials and processing parameters; -How to achieve anisotropic strengthening by selecting variants of which the desirable slip systems are in the preferential direction? The technical effort is featured by a closely integrated computational and experimental approach to (1) clarify the effect of materials parameters in variant selection at the nucleation and early growth stage during thermomechanical treatment, (2) fabricate single-crystalline samples, and (3) investigate the anisotropic strengthening during tensile and creep deformation. This program will be focused on nickel-based alloys due to its wide-spread applications. However, the fundamental mechanism elucidated is applicable to most alloys that contain coherent precipitates, e.g., novel refractory alloys.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.