Nucleation in Solid Metallic Solutions with Steep Composition Gradients

技术概要：当金属间相通过元素的扩散混合形成时，陡峭的化学梯度可以抑制成核，通常导致非平衡或亚稳相的形成。所提出的努力适用于实验和计算工具，以增加我们的理解这些陡峭的成分梯度内的固态成核。更具体地说，纳米量热法、原位DTEM、原位TEM和临界浓度梯度理论的独特组合用于识别和预测在缓慢（10^1 K/s）和快速加热速率（10^5 K/s）下，在模型层状材料系统（Ni-Al）中首先形成哪些相以及在什么温度下形成。Ni-Al样品将沉积在具有双层厚度（10至150 nm）和平均组成（0.1至0.9）的范围的纳米量热计上。此外，输入的浓度梯度模型将得到加强，以提高预测通过计算相关阶段的界面能，并通过量化的速率和路径的相互扩散的Ni-Al双层样品。有了这些增强的手，加热速率，双层厚度，和平均组合物将改变实验和计算，以评估这种浓度梯度模型的有效性，在预测哪个阶段首先成核。非专业总结：拟议的努力旨在提高我们对固体部件（如金属和陶瓷保护涂层，多孔材料和MEMS器件）制造过程中化合物如何形成的理解。将使用独特的实验和计算工具，并进行一系列实验，以评估临界浓度梯度模型预测第一阶段成核的能力。 改进我们的模型和对成核的理解将有助于未来的研究人员为包括航空航天、汽车和微电子在内的各种行业开发改进的材料。PI将涉及至少一名来自巴尔的摩西部高中的女高中生。这名高中生将与一名博士生合作完成这个项目，该博士生已经指导过霍普金斯的本科生。 暑期工资将通过拟议的预算为学生提供。PI还计划在本学年招收一名本科生参加该项目，并将努力招收妇女和少数民族等代表性不足的群体。最后，PI将促进霍普金斯校区的创业活动，通过他指导的领导力教育中心监督博士生和博士后的专业发展模块的引入。 他还将利用自己的创业经验，通过帮助发展孵化器和创业文化，在校园内促进类似的努力。

TECHNICAL SUMMARY: When intermetallic phases form through diffusional mixing of elements steep chemical gradients can inhibit nucleation, often leading to the formation of nonequilibrium or metastable phases. The proposed effort applies experimental and computational tools to increase our understanding of solid-state nucleation within these steep composition gradients. More specifically, a unique combination of nanocalorimetry, in situ DTEM, in situ TEM, and critical concentration gradient theory is used to identify and predict which phases form first and at what temperatures in a model, layered material system (Ni-Al) under both slow (10^1 K/s) and fast heating rates (10^5 K/s). The Ni-Al samples will be deposited on nanocalorimeters with a range of bilayer thicknesses (10 to 150 nm) and average compositions (0.1 to 0.9). In addition, inputs to the concentration gradient model will be enhanced to improve predictions by calculating interface energies for the relevant phases and by quantifying the rates and paths of interdiffusion in the Ni-Al bilayer samples. With these enhancements in hand, heating rate, bilayer thickness, and average composition will be varied experimentally and computationally to assess the effectiveness of this concentration gradient model in predicting which phase nucleates first. NON-TECHHNICAL SUMMARY: The proposed effort is designed to enhance our understanding of how compounds form during the fabrication of solid components such as metallic and ceramic protective coatings, porous materials and MEMS devices. Unique experimental and computational tools will be used and a series of experiments will be performed to assess the ability of a critical concentration gradient model to predict the first phase to nucleate. Improving our models and understanding of nucleation will help future researchers develop improved materials for a variety of industries including aerospace, automobile and microelectronics. The PI will involve at least one female high school student from Western High School in Baltimore. The high school student will be teamed with a PhD student on this project, who has already mentored undergraduate students at Hopkins. Summer salary will be provided for the student through the proposed budget. The PI also plans to recruit one undergraduate student to join the project during the school year and efforts will be made to recruit under-represented groups such as women and minorities. Lastly, the PI will promote entrepreneurial activities on the Hopkins Campus by overseeing the introduction of professional development modules for PhD students and Postdocs through the Center for Leadership Education that he directs. He will also draw on his own entrepreneurial experience to promote similar efforts on campus by helping to grow an incubator and an entrepreneurial culture.