Bottom-up Synthesis of Nanocrystalline Intermetallic Coatings with Controlled Microstructures

由金属合金制成的涂层广泛应用于从机床到汽车、飞机和火力发电厂等行业。这些涂层增加了耐磨性、耐腐蚀性和抗氧化性，并提高了结构和功能部件的性能。因此，定制金属合金涂层性能的能力将显著提高汽车和飞机发动机、切削工具、发电厂涡轮机和管道的效率和寿命。该奖项支持旨在控制金属合金涂层微观结构（小尺度晶体的大小、形状和分布）的基础研究。由于机械、化学和热性能与微观结构密切相关，因此pi可以根据不同的应用调整涂层的性能。研究活动与教育和推广工作相结合，包括本科生指导计划，高中生科学演示以及材料合成和表征研究生培训。目前使用化学或物理沉积方法合成金属合金涂层的方法对微观结构的控制能力有限。该项目旨在开发一种新的自下而上的工艺，利用物理气相沉积合成具有定制微结构的金属间化合物涂层。该项目的中心假设是，通过在生长过程中有条不紊地播种纳米晶体，非晶金属间涂层可以在随后的适当温度退火过程中可控地结晶。该项目将阐明这一过程的基本物理原理，并通过合成和表征具有可控晶粒尺寸、长径比和空间分布的纳米结构铝化钛（TiAl）涂层来证明其实际可行性。此外，利用原位透射电子显微镜和x射线衍射实验研究合成TiAl涂层的微观组织演变、稳定性和力学行为，以了解其结晶动力学和结构-性能关系。

Coatings made of metallic alloys are used in a wide range of industries from machine tools to automobiles, aircraft and thermal power plants. These coatings increase resistance to wear, corrosion and oxidation and enhance the performance of structural and functional components to which they are applied. Thus, the ability to tailor the properties of metallic alloy coatings would lead to significant improvements in the efficiency and lifetime of automobile and aircraft engines, cutting tools and power plant turbines and tubings. This award supports fundamental research that aims to control the microstructure (size, shape and distribution of small-scale crystallites) of metallic alloy coatings. Since the mechanical, chemical and thermal properties are intimately connected to the microstructure, this would allow the PIs to tune the properties of the coatings for various applications. The research activity is integrated with education and outreach efforts that include a mentoring program for undergraduates, scientific demonstrations for high school students and training of graduate students in materials synthesis and characterization. Current methods to synthesize metallic alloy coatings using either chemical or physical deposition processes provide only limited capability for controlling the microstructure. This project aims to develop a new bottom-up process to synthesize intermetallic coatings with tailored microstructures using physical vapor deposition. The central hypothesis of the project is that by methodically seeding nanocrystals during the growth process, amorphous intermetallic coatings can be controllably crystallized during subsequent annealing at the appropriate temperature. The project will elucidate the fundamental physics of this process and demonstrate its practical viability by synthesizing and characterizing nanostructured titanium aluminide (TiAl) coatings with controlled grain size, aspect ratio and spatial distribution. In addition, microstructural evolution, stability and mechanical behavior of the synthesized TiAl coatings will be investigated using in situ transmission electron microscopy and X-ray diffraction experiments to understand the crystallization kinetics and structure-property relationships.