THERMAL AND MECHANICAL PROPERTIES OF NOVEL CARBIDE MATERIALS

<p>"This research focuses on studying the thermal and mechanical properties of novel carbide materials at room and elevated temperatures. The novel carbide materials investigated include zeta phase tantalum carbide (ζ-Ta₄C_3-x) and a high entropy (Ta,Hf,Nb,Zr)C carbide. The electrical resistivity and thermal conductivity of zeta phase tantalum carbide (~96 wt.%) were measured as 160 ± 4.2 μΩ-cm and 9.6 W/m•K. These are higher and lower (respectively) than for cubic tantalum carbide, most likely due to planes of carbon vacancies present in the ζ-Ta₄C_3-x crystal structure. The thermal conductivity of (Ta,Hf,Nb,Zr)C was lower than any of its carbide constituents with values ranging from 10.7 W/m•K at room temperature to 39.9 W/m•K at 2000°C. The electrical resistivity was higher than any of the carbide constituents ranging from 80.9 μΩ•cm at room temperature to 114.1 μΩ•cm at 800 °C. The electron contribution to thermal conductivity increased with temperature, and the phonon contribution was unaffected by temperature. The strength and fracture toughness of tantalum carbide ceramics (~75 wt.% ζ-Ta₄C_3-x) were 710 ± 36.5 MPa and 10.2 ± 0.4 MPa· m1/2 at room temperature and decreased to 180 ± 19.7 MPa and 4.7 ± 0.1 MPa· m1/2 at 1600°C. The high aspect ratio grains (along the long axis) appeared to be the critical flaw. A brittle to ductile transition was observed between 1400°C and 1600°C. The ductility was attributed to deformation via kinking and delamination observed in the microstructure at room temperature. ζ-Ta₄C_3-x was observed to be machinable with traditional tools such as a hacksaw, drill bit, and end mill. The machinability is attributed to cleaving of grains along weakly bonded planes and prevention of crack propagation into the bulk ceramic"--Abstract, p. iv</p>

Name thesis:degree_name

Ph. D. in Ceramic Engineering

Grantor

Missouri University of Science and Technology

Author dc:creator

• Schwind, Evan Charles

• High Entropy Carbide
• Mechanical Properties
• Tantalum Carbide
• Thermal Properties
• Ultra-High Temperature Ceramics
• Zeta Phase
• Ceramic Materials
• Engineering

Repository record dc:identifier

https://scholarsmine.mst.edu/doctoral_dissertations/3185

OAI identifier oai:identifier

oai:scholarsmine.mst.edu:doctoral_dissertations-4190