Multiscale corrosion of zirconium carbide, carbon, and CF/ZRC under extreme environments

Konnik, Matt T.

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https://hdl.handle.net/2142/127368 Copy

Description

Title

Multiscale corrosion of zirconium carbide, carbon, and CF/ZRC under extreme environments

Author(s)

Konnik, Matt T.

Issue Date

2024-11-26

Director of Research (if dissertation) or Advisor (if thesis)

• Stephani, Kelly A
• Panerai, Francesco

Doctoral Committee Chair(s)

• Stephani, Kelly A
• Panerai, Francesco

Committee Member(s)

• Elliott, Greg
• Panesi, Marco
• Sankaran, R. Mohan

Department of Study

Mechanical Sci & Engineering

Discipline

Mechanical Engineering

Degree Granting Institution

University of Illinois at Urbana-Champaign

Degree Name

Ph.D.

Degree Level

Dissertation

Keyword(s)

• high temperature
• ultra-high temperature
• corrosion
• dry corrosion
• materials
• ceramic
• carbon
• carbide
• oxide
• nitride
• zirconium carbide
• zirconia
• carbon fibers
• oxidation
• nitridation
• composite
• thermal plasma
• inductively coupled plasma
• spectroscopy
• microstructure
• extreme environment
• thermal transport
• thermal protection systems
• defects

Abstract

The development of materials capable of withstanding extreme environments is critical for fields such as aerospace, energy, and defense, where conventional materials often fail. In the context of high-temperature air environments, such as those seen in hypersonics, highly reactive gas species, such as oxygen, are a primary mechanism by which most protection system materials degrade during service. This ultimately leads to changes in structure, which in turn alter properties, necessitating a fundamental understanding of ultra-high temperature corrosion processes and consequences to appropriately design, predict, and innovate protective materials. To that end, this dissertation focuses on driving mechanisms and structure-property relationships associated with oxidative corrosion in ultra-high temperature environments for hypersonic thermal protection system materials, including zirconium carbide (ZrC), disordered carbons, and carbon fiber/zirconium carbide (Cf/ZrC) composites. Initial analysis focused on the ultra-high temperature oxidation behavior of hot-pressed substoichiometric zirconium carbide in a highly controlled test environment. Investigations were performed using isothermal flow-tube furnace experiments at temperatures ranging from 1000 to 1600 °C. Auxiliary gas composition influence on the oxidation behavior was studied by introducing oxygen to substrates held under either pure argon or nitrogen environments, creating two distinct material sets for comparison. During furnace ramp-up, prior to isothermal oxygen exposure, nitrogen was found to infiltrate the substrate resulting in ZrCxNy (carbonitride) formation which provided superior oxidation resistance to the as-received ZrC0.63. Ex situ investigation of ceramic-oxide interfacial regions revealed the presence of carbon precipitate in both material sets at treatment temperatures of up to 1400 °C, along with the presence of an ZrCxOy (oxycarbide) system, providing supporting evidence for a two-step oxidation mechanism. At sufficiently high-test temperatures, resulting scale formations for the N2/O2 test specimens were found to be less porous than the Ar/O2 counterparts, with a higher degree of cubic-/tetragonal-ZrO2 crystallites present at room temperature attributed to nitrogen incorporation into the anion sublattice of ZrO2. In more application-relevant conditions, inductively coupled air plasma (ICP) was used to simulate stagnation point heating seen in hypersonic flight environments. Zirconium carbide specimens were subjected to high-enthalpy air flow at surface temperatures between 1850 and 2525 °C. Corrosion was found to progress linearly and quasi-linearly in time. Electron microscopy resolved scale crack formations to be the preferred method of surface gas exchange at lower surface temperatures with a shift to porosity at higher temperatures. Roughness and autocorrelation lengths of resulting scale formations were found to be similar between specimens, but with a distinct increase resulting from higher power exposure indicating a potential kinetic roughening effect. Total hemispherical reflectance measurements were used to determine room-temperature emittance and optical bandgap, while supporting diffraction and Raman profiles correlate differences in these optical properties to the presence of nitrogen and potential carbonate species. Scale porosity was observed to decrease with increasing test temperatures, while gradients formed at higher temperatures, attributed to shifting in dominance of transport effects. Raman microscopy indicated aggregate reaction-limited corrosion processes, though the most extreme conditions saw transport influence on long timescales. XPS identified bulk scale reaction products as oxides and ternary oxynitrides. Scale-carbide interfaces included oxynitrides, oxycarbides, carbonitrides, along with carbon precipitates at lower temperatures. Plasma dwell time significantly influenced the local electron density of in-depth zirconium, possibly due to oxygen vacancy accumulation mediated by high temperatures and free electrons. Thermal transport in carbon fibers and amorphous carbon was investigated through equilibrium molecular dynamics simulations, revealing key insights relevant to ablative thermal protection systems and ceramic matrix composites. Pristine carbon fibers displayed orthotropic conductivities around 3 W·m−1·K−1, while amorphous carbon showed isotropic behavior with conductivity of 1.8 W·m−1·K−1. The Green-Kubo relation was used to extract ensemble averaged heat currents, allowing statistically significant analysis of defect impacts. Impurities from manufacturing introduced a small but significant reduction in conductivity, while oxygen, whether distributed through the bulk or as an oxide layer, reduced conductivity by up to 50% in pristine fibers and 40% in amorphous carbon. Etch pitting also lowered thermal conductivity significantly, suggesting early consideration of pitting effects is necessary. However, the inherent disorder in these systems blunted the impact of defects compared to crystalline materials like graphene, where phonon-defect scattering is more pronounced. This disorder, even in pristine states, leads to intrinsic scattering mechanisms, reducing the overall sensitivity to defects. The Cf/ZrC system was examined under various ultra-high temperature conditions, including flow-tube furnace, oxyacetylene flame, and stagnation point heating in thermal air plasma, providing key insights into its corrosion behavior. This work elucidates major environment-structure-property characteristics of zirconium carbide, disordered carbons, and Cf/ZrC subject to ultra-high temperature air, focusing on lacking areas of the current body of literature. The findings presented in this work prove to advance appropriate selection, design, prediction, and innovation efforts by identifying key corrosion mechanisms, quantifying structure, and offering potential pathways for improving oxidation resistance and thermal performance in extreme environments.

Graduation Semester

2024-12

Type of Resource

Thesis

Handle URL

https://hdl.handle.net/2142/127368

Copyright and License Information

Copyright 2024 Matthew T. Konnik

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