Doctoral Dissertations

Keywords and Phrases

Diboride; Fusion welding; Ultra high temperature ceramics

Abstract

"Plasma and pulsed plasma arc welding (PAW and PPAW) processes were used to fusion weld ZrB2 containing 20 vol% ZrC. Varying welding parameters resulted in changes in weld pool shape and size, and the size of ZrB2 grains within the fusion zone. For PAW processes that resulted in a keyhole fusion zone (full penetration), the arc to workpiece power transfer efficiency was estimated to be 2 grain lengths were observed to decrease between binary PAW FZs (~1 mm in length), and binary PPAW FZs (~0.8 mm in length), and an increasing aspect ratio for ZrB2 grains in PPAW welds (up to 40:1) compared to PAW ZrB2 grain aspect ratios (up to 25:1) revealed that growth of ZrB2 was hindered in PPAW FZs. Grain growth was also observed to decrease with decreasing arc power. A high arc power resulted in high growth rates of ZrB2 and a textured FZ, lower arc power FZs did not exhibit texture. A high current plasma arc (222 A) was used to increase the temperature of the weld pool, such that ZrB2 growth would follow the arc thermal gradient. ZrB2 growth occurred in the basal plane, giving grains a plate-like structure, where grain thickness increased by ledge growth. ZrB2 grain sizes within the FZ were observed to affect the strength of weldments. PM flexure strengths were measured to be ~660 MPa and strengths were observed to drop to ~140 MPa for PAW weldments and ~170 MPa for PPAW weldments. Diffusion of C into the melt pool was observed to hinder ZrB2 grain growth significantly (~150 µm maximum ZrB2 grain size), and the average flexure strength of a ZrB2-ZrC-C weldments was ~250 MPa."--Abstract, page iv.

Advisor(s)

Hilmas, Greg
Fahrenholtz, William

Committee Member(s)

Smith, Jeffrey D.
Asle Zaeem, Mohsen
Switzer, Jay A., 1950-

Department(s)

Materials Science and Engineering

Degree Name

Ph. D. in Ceramic Engineering

Sponsor(s)

United States. Air Force. Office of Scientific Research

Comments

This research was funded by the Air Force Office of Scientific Research, grant number FA9550-12-C-0060.

Publisher

Missouri University of Science and Technology

Publication Date

Spring 2015

Journal article titles appearing in thesis/dissertation

  • Plasma arc welding of ZrB2-20 vol% ZrC ceramics
  • Mechanical behavior and applications of arc welded ceramics
  • Growth of ZrB2 in plasma arc welded ZrB2-20 vol% ZrC
  • Plasma arc welding of TiB2-20 vol% TiC

Pagination

xv, 183 pages

Note about bibliography

Includes bibliographic references.

Rights

© 2015 Derek Scott King, All rights reserved.

Document Type

Dissertation - Open Access

File Type

text

Language

English

Subject Headings

Plasma arc weldingCeramicsHeat resistant materialsCarbides

Thesis Number

T 10717

Electronic OCLC #

913397356

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