In situ Formation of Refractory Carbide Coatings with Protective Magneli Phases

该奖项的研究目标是了解陶瓷涂层(过渡金属氧化物和原位形成的碳化物)中的缺陷结构如何决定碳基复合材料和泡沫等多孔固体的热/氧化和摩擦/磨损性能的机制。具体地说，该项目将探索(A)间隙碳化物和氧化物相(如ZrC和ZrO2)如何提供对碳的耐热和抗氧化性，以及(B)润滑性纳米晶层状陶瓷(如高基本堆积故障密度的氧化锌)和低晶体剪切、缺氧的Magnéli相(如TiO2x)如何减轻摩擦和磨损。结合经典的分子动力学模拟和从头算密度泛函理论计算，研究了C/ZrC/ZrO2的界面行为，并表征了层状低结晶剪切陶瓷涂层的缺陷化学、热力学性质和机械/摩擦学行为。这项研究将有助于回答两个重要问题：(1)涂层系统能否处理具有热力学和动力学稳定性的氧化物和碳化物相及界面？(2)这些相的缺陷结构(平面层错和空位/间隙)如何在提供足够的硬度和弹性模量的同时适应界面剪切？如果成功，本研究的结果也可以应用于其他原位形成间隙碳化物相的耐火氧化物涂层，并对其产生更广泛的影响。预计航空航天和其他工业用碳基复合材料和泡沫的使用温度将进一步提高，因为这些保护涂层只需最低限度的加工，并在使用过程中进行原位修改，以改善机械和摩擦学性能。研究生的教育活动将包括实验和建模组件，旨在了解碳化物和氧化物形成的基本热化学机制以及它们的氧化、热和高温性质。此外，本科生将通过高级设计项目积极参与这项研究。该项目将向参加德克萨斯州州长学校的高二学生介绍陶瓷科学和表面工程研究，德克萨斯州长学校是北卡罗来纳大学的夏季学术增收夏令营。更广泛的影响也将通过向NSF资助的致力于摩擦的网络基础设施：原子级摩擦研究和教育协同中心(RESH)的贡献来实现。

The research objective of this award is to understand the mechanisms of how defect structure in ceramic coatings (transition metal oxides and in situ formed carbides) determines the thermal/oxidative and friction/wear properties in cellular solids, such as carbon-based composites and foams. Specifically, this project will explore (a) how interstitial carbide and oxide phases, such as ZrC and ZrO2, provide thermal and oxidation resistance to carbon, and (b) how lubricious, nanocrystalline layered ceramics, such as high basal stacking fault density ZnO, and low crystallographic shear, oxygen deficient Magnéli phases, such as TiO2-x, mitigate friction and wear. In conjunction, classical molecular dynamics simulations and ab initio Density Functional Theory calculations will be implemented to study the interfacial behavior of C/ZrC/ZrO2 as well as to characterize the defect chemistry, thermodynamic properties, and mechanical/tribological behavior of the layered, low crystallographic shear ceramic coatings. This research will help answer two important questions: (1) Can the coating systems be processed with thermodynamically and kinetically stable oxide and carbide phases and interfaces? (2) How will the defect structure (planar stacking faults and vacancies/interstitials) of these phases be able to accommodate interfacial shear while providing sufficient hardness and elastic modulus?If successful, the results of this research could also be applied and have broader impact to other refractory oxide coatings that form in situ interstitial carbide phases. Further enhancement in operating temperatures of carbon-based composites and foams for aerospace and other industries is expected with these protective coatings that require minimal processing and undergo in situ modifications during use to improve mechanical and tribological properties. Educational activities for graduate students will involve experimental and modeling components aimed to understand the fundamental thermochemical mechanisms of carbide and oxide formation and their oxidative, thermal and high temperature properties. Additionally, undergraduate students will be actively involved in this research through senior design projects. The project will introduce ceramic science and surface engineering research to high school sophomores attending the Texas Governor's School, a summer academic enrichment camp at UNT. Broader impact will also be realized through contributions to an NSF-funded cyberinfrastructure dedicated to friction: Atomic-scale Friction Research and Education Synergy Hub (AFRESH).