Doctoral Dissertations

Keywords and Phrases

borides; carbides; ceramics; oxidation; properties; sintering

Abstract

"The study explores the pressure less sintering (PS) and chemical compatibility of ZrB2-30 vol.%SiC produced by additive manufacturing (AM) with CO2. The oxidation kinetics and scale microstructures were compared for ZrB2-SiC made by hot pressing (HP) and by AM coupled with PS. All specimens exhibited parabolic oxidation kinetics. The difference in oxidation behavior becomes evident at temperatures of 1100-1400°C (200-900h). Oxidation rates increased as grain size increased. Similar oxide scale morphologies were observed in both CO2 and air, with an outer borosilicate layer and an inner porous ZrO2 layer containing partially oxidized SiC particles and residual borosilicate products. In air, oxide scale thicknesses were roughly double those in CO2 at all temperatures. Activation energies for oxidation were found to be 140 ± 20 kJ/mol in air and 110 ± 20 kJ/mol in CO2, suggesting comparable rate-limiting diffusion. Evolution of microstructure, densification, and grain coarsening, during the PS of AM-ZrB2-SiC have been studied. The apparent activation energy for sintering was determined to be 940±70 kJ/mol, suggesting lattice diffusion as the dominant sintering mechanism. The grain growth exponent was n=2 of both ZrB2 and SiC, indicating diffusion-controlled coarsening. The activation energies of grain growth were the same for ZrB2 and SiC, implying the same coarsening mechanisms. Vicker’s hardness (20 GPa) and Young’s modulus (480±20 GPa) were similar to HP specimens; however, the flexural strength (270±42 MPa) was lower than HP counterparts by a factor of 2-3 due to the presence of large pores introduced in AM process" -- Abstract, p. iv

Advisor(s)

Lipke, David W.

Committee Member(s)

Fahrenholtz, William
O'Malley, Ronald J.
Watts, Jeremy Lee, 1980-
Leu, M. C. (Ming-Chuan)

Department(s)

Materials Science and Engineering

Degree Name

Ph. D. in Ceramic Engineering

Publisher

Missouri University of Science and Technology

Publication Date

Summer 2024

Pagination

xv, 124 pages

Note about bibliography

Includes_bibliographical_references_(pages 51, 81, 106 & 115-122)

Rights

©2024 Marharyta Lakusta , All Rights Reserved

Document Type

Dissertation - Open Access

File Type

text

Language

English

Thesis Number

T 12391

Download

Share

 
COinS