Processing, microstructure, and mechanical properties of zirconium diboride-molybdenum disilicide ceramics and dual composite architectures

<p>"This research had two objectives: characterization of processing-microstructure-mechanical property relationships of conventional ZrB₂-MoSi₂ ceramics at room temperature (RT) and 1500⁰C in air, and fabrication of ZrB₂-MoSi₂ dual composite architectures (DCAs) for use near 1500⁰C. Elastic moduli, fracture toughness, and flexure strength were measured at RT and 1500⁰C for 15 ZrB₂-MoSi₂ ceramics hot pressed using fine, medium, or coarse ZrB₂ starting powder with 5-70 vol.% MoSi₂, referred to as FX, MX, and CX respectively where X is the nominal MoSi₂ content. MoSi₂ decomposed during sintering, resulting in microstructures with ZrB₂ cores and (Zr_1-xMo_x)B₂ shells via surface and grain boundary diffusion. Flexure strength at RT (700-800 MPa for FX, 560-720 MPa for MX, and 440-590 MPa for CX) was controlled by the maximum ZrB₂ grain size, and toughness (2.7-3.9 MPa·m^1/2) did not trend with MoSi₂ content. At 1500⁰C toughness increased with MoSi₂ content and ZrB₂ grain size, and strength of FX and MX was controlled by oxidation damage at 1500⁰C. Strength of CX followed the opposite trend, with C10 exhibiting a strength of ~600 MPa.</p><p>Four ZrB₂-MoSi₂ DCAs were fabricated by dispersing granules of selected ZrB₂-MoSi₂ compositions in matrices of different ZrB₂-MoSi₂ compositions. Strength limitation at 1500⁰C by differential oxidation of granules and matrix was resolved by compositional adjustment, but microcracking due to granule-matrix CTE mismatch limited strength to ~140 MPa at RT and ~360 MPa at 1500⁰C. The granule-matrix interface did not deflect cracks, and the toughness at 1500⁰C was 6.1-6.9 MPa·m^1/2, similar to that of conventional ZrB₂-MoSi₂ ceramics. CTE matching via addition of a third phase and use of a weak granule-matrix interface are recommended areas of focus for future development of high-temperature DCAs"--Abstract, page iv.</p>

Name thesis:degree_name

Ph. D. in Materials Science and Engineering

Grantor

Missouri University of Science and Technology

Author dc:creator

• Grohsmeyer, Ryan Joseph

• High-Temperature Ceramics
• Mechanical Properties
• Microstructure
• Molybdenum Disilicide
• Processing
• Zirconium Diboride
• Energy Systems
• Materials Science and Engineering

Repository record dc:identifier

https://scholarsmine.mst.edu/doctoral_dissertations/2561

OAI identifier oai:identifier

oai:scholarsmine.mst.edu:doctoral_dissertations-3566