In situ Formation of Refractory Carbide Coatings with Protective Magneli Phases

University Of North Texas, Denton TX

Investigators

Abstract

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).