Doctoral Dissertations

Abstract

"Research presented in this dissertation focused on the production of ZrB₂-SiC composites and their characterization; in particular their mechanical properties and thermally generated residual stresses. Thermally generated stresses were measured using Raman spectroscopy as well as both neutron and x-ray diffraction. For 70 vol% ZrB₂ - 30 vol% SiC composites neutron diffraction revealed that the SiC phase was under ~880 MPa compressive stress and the ZrB₂ phase was under ~450 MPa tension at room temperature. It was also discovered that stresses began to accumulate at ~1400 ⁰C upon cooling from the processing temperature (1900 ⁰C -2000 ⁰C). Raman spectroscopy and x-ray diffractions agreed well with one another and showed the stresses in the SiC phase on the surface of the samples to be ~350 MPa; lower than that in the bulk as measured by neutron diffraction. It has also been shown that annealing composites at temperatures below 1400 ⁰C, particularly while under pressure can partially relieve these stresses leading to increases in mechanical strength of as much as 30%. The role of the particle size of the SiC phase was also investigated. For SiC particle sizes smaller than 11.5 µm, the failure strengths of the composites followed a 1/c1/2 type relationship as predicted by Griffith. Above that particle size however, strength, modulus, and hardness all decreased rapidly. It was discovered that for SiC particle sizes larger than 11.5 µm microcracking occurred resulting in the decrease of the measured mechanical properties"--Abstract, page iv.

Advisor(s)

Hilmas, Greg

Committee Member(s)

Bohannan, Eric W., 1969-
Brow, Richard K.
Fahrenholtz, William
Dharani, Lokeswarappa R.

Department(s)

Materials Science and Engineering

Degree Name

Ph. D. in Materials Science and Engineering

Sponsor(s)

United States. Air Force. Office of Scientific Research

Publisher

Missouri University of Science and Technology

Publication Date

Summer 2011

Journal article titles appearing in thesis/dissertation

  • Stress measurements in ZrB₂-SiC composites using Raman spectroscopy and neutron diffraction
  • Measurement of thermal residual stresses in ZrB₂-SiC composites
  • Mechanical characterization of ZrB₂-Sic composites with varying SiC particle sizes
  • Mechanical characterization of annealed ZrB₂-SiC composites

Pagination

xv, 187 pages

Note about bibliography

Includes bibliographical references.

Rights

© 2011 Jeremy Lee Watts, All rights reserved.

Document Type

Dissertation - Open Access

File Type

text

Language

English

Library of Congress Subject Headings

Annealing of crystals
Ceramics -- Mechanical properties
Residual stresses -- Measurement

Thesis Number

T 9788

Print OCLC #

775789870

Electronic OCLC #

752505161

Share

 
COinS