Doctoral Dissertations

Keywords and Phrases

Failure analysis; Hot pressing; Ultra-high temperature ceramics

Abstract

"Research presented in this dissertation focused on the mechanical behavior of ZrB₂ based ceramic at elevated temperatures. Flexure strength, fracture toughness, and elastic modulus were measured at temperatures up to 2300ºC for three compositions: monolithic ZrB₂ (Z); ZrB₂ - 30 vol% SiC - 2 vol% B₄ C (ZS); and ZrB₂ - 10 vol% ZrC (ZC). In argon, Z, ZS, and ZC had strengths of 210 (at 2300ºC), 260 (at 2200ºC), and 295 MPa (at 2300ºC), the highest temperatures tested for each composition. Fractography was used extensively to characterize the strength limiting flaws as a function of temperature. Strength of ZS in argon was controlled by the SiC cluster size up to 1800ºC, and the formation of B-O-C-N phases that bridged SiC clusters above 2000ºC. For ZC, surface flaws introduced during specimen preparation were the source of critical flaws in the material up to 1400ºC, sub-critical crack growth of surface flaws between 1600 and 2000ºC, and microvoid coalescence above 2000ºC.

It was also shown that thermal annealing at either 1400, 1500, or 1600ºC improves the strength and modulus of ZS at temperatures between 800ºC and 1600ºC. Heat treatment at 1400ºC for 10 hours produced the largest improvement in strength, 430 MPa at 1600ºC versus 380 MPa for the as processed material. As a whole, the research pointed to several key microstructural features currently limiting the mechanical properties at the highest temperatures. In particular, removal of unfavorable secondary phases, and improved control over microstructure, should be promising methods to improve the elevated temperature properties of ZrB₂ ceramics."--Abstract, page iv.

Advisor(s)

Hilmas, Greg

Committee Member(s)

Fahrenholtz, William
Smith, Jeffrey D.
Miller, F. Scott, 1956-
Chandrashekhara, K.

Department(s)

Materials Science and Engineering

Degree Name

Ph. D. in Ceramic Engineering

Sponsor(s)

United States. Air Force. Office of Scientific Research

Publisher

Missouri University of Science and Technology

Publication Date

Spring 2014

Journal article titles appearing in thesis/dissertation

  • Strength of zirconium diboride to 2300ºC
  • Mechanical behavior of zirconium diboride-silicon carbide ceramics at elevated temperatures in air
  • Mechanical behavior of zirconium diboride-silicon carbide ceramics up to 2200ºC
  • Elevated temperature strength enhancement of ZrB₂-30 vol% SiC ceramics by post-sintering thermal annealing
  • Ultra-high temperature strength, toughness and modulus of a zirconium diboride-zirconium carbide ceramic
  • Building an ultra-high-temperature mechanical testing system

Pagination

xix, 259 pages

Note about bibliography

Includes bibliographical references.

Rights

© 2014 Eric William Neuman, All rights reserved.

Document Type

Dissertation - Open Access

File Type

text

Language

English

Subject Headings

Ceramic materials -- Mechanical properties
Ceramics -- Thermal properties
Zirconium -- Thermal properties
Borides -- Thermal properties

Thesis Number

T 10465

Electronic OCLC #

882484118

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