Doctoral Dissertations

Keywords and Phrases

Hot pressing

Abstract

"A systematic study on densification behavior of TaC by hot pressing over a range of temperatures from 1900°C to 2400°C revealed the microstructural development as a function of hot pressing temperature. Grain growth started around 2350°C while the relative density reached 95%. Grain growth became rapid at 2400°C and resulted in entrapped porosity which prevented further densification. The addition of a small amount (0.36 wt% to 0.78 wt%) of an oxide reducing additive, such as B₄C and/or C, significantly enhanced the densification of TaC, achieving 98% relative density at 2200°C. However, the onset temperature for rapid grain growth was also reduced. The competition between densification and grain growth inhibited the achievement of full density. Grain growth was pinned by adding excess B₄C. Near full density was obtained for TaC with 1 or 2 wt% B₄C additions by hot pressing at 2100°C without observable grain growth. However, it was found that grain growth was pinned by the new phases including TaB₂ and C (instead of B₄C) formed by the reaction between TaC and B₄C. The achievement of near full density allowed for mechanical property measurements.

The formation of refractory TaB₂ in the TaC-B₄C system has raised the interest in studying the densification and mechanical properties of TaC-TaB₂ composites. However, the mechanical properties of TaB₂ have not been reported in the literature and a considerable amount of discrepancy exists. Therefore, a study of the basic mechanical properties of TaB₂ was also completed. Phase pure TaB₂ was synthesized by reducing Ta₂O₅ using B₄C and graphite at 1600°C, having an average particle size of 0.4 µm. The TaB₂ was hot pressed to 98% relative density at 2100°C with an average grain size of 5.3 µm. Mechanical properties were measured on hot pressed TaB₂"--Abstract, page iv.

Advisor(s)

Hilmas, Greg
Fahrenholtz, William

Committee Member(s)

Smith, Jeffrey D.
Huebner, Wayne
Waddill, George Daniel

Department(s)

Materials Science and Engineering

Degree Name

Ph. D. in Ceramic Engineering

Sponsor(s)

U.S. Army Space and Missile Defense Command

Comments

Funded by the U.S. Army Space and Missile Defense Command grant number DASG60-03-l-OO 11.

Publisher

Missouri University of Science and Technology

Publication Date

Summer 2008

Journal article titles appearing in thesis/dissertation

  • Crystal structure and bonding of transition metal carbides
  • Densification and mechanical properties of TaC-based ceramics
  • Synthesis, densification, and mechanical properties of TaB₂
  • Densification, mechanical properties, and oxidation resistance of TaC-TaB₂

Pagination

xv, 124 pages

Note about bibliography

Includes bibliographical references.

Rights

© 2008 Xiaohong Zhang, All rights reserved.

Document Type

Dissertation - Restricted Access

File Type

text

Language

English

Subject Headings

BoridesCarbidesCeramic materials -- Mechanical propertiesTantalum

Thesis Number

T 9469

Print OCLC #

606910075

Electronic OCLC #

905917959

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