Doctoral Dissertations

Keywords and Phrases

borides; carbides; fusion welding; joining

Abstract

"This research focuses on the joining of ultra-high temperature ceramics to either themselves or refractory metals/alloys via fusion welding and the mechanical strength of produced joints. The ceramics studied consisted of compositions within a diboride-carbide-carbide ternary system while metals studied consisted of molybdenum and a molybdenum alloy. SiC-ZrB2-ZrC ceramics on a binary join between pure SiC and the ternary eutectic composition were found to be weldable when SiC content was below ~57.5 vol%. Compositions above 57.5 vol% SiC were unweldable based on pitting and off-gassing behavior. Welded strength of ceramics was ~180-300 MPa in the SiC-ZrB2-ZrC ternary eutectic composition, ~180-220 MPa in the SiC-ZrB2 binary eutectic composition, and ~130-180 MPa in a 60 vol% SiC – 40 vol% ZrB2 composition at room and elevated tempeatures. Welded strength was limited by pore size within the fusion zones. Thermal conductivity and electrical resistivity of parent materials in metal-ceramic welds were investigated to determine their effect on weldability. Welds were formed between molybdenum, or a molybdenum alloy, and ceramic compositions on a binary join between nominally pure ZrB2 and the SiC-ZrB2-ZrC ternary eutectic composition. Neither thermal conductivity nor electrical resistivity was found to affect weldability; however, melting temperature of ceramic coupons affected overall weld symmetry and penetration. Welded strength of joints between a molybdenum alloy and a 70 vol% ZrB2 – 19.5 vol% SiC – 10.5 vol% ZrC ceramic were ~10-100 MPa and failed due to the pores and cracks within produced samples. Removal of SiC from ceramics was found to reduce porosity and cracking in fusion zones"--Abstract, p. iv

Advisor(s)

Watts, Jeremy Lee, 1980-

Committee Member(s)

Fahrenholtz, William
Hilmas, Greg
Smith, Jeffrey D.
Chandrashekhara, K.

Department(s)

Materials Science and Engineering

Degree Name

Ph. D. in Ceramic Engineering

Publisher

Missouri University of Science and Technology

Publication Date

Spring 2022

Pagination

xiv, 190 pages

Note about bibliography

Includes_bibliographical_references_(pages 178-189)

Rights

© 2022 Jecee Jarman, All Rights Reserved

Document Type

Dissertation - Open Access

File Type

text

Language

English

Thesis Number

T 12228

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