Masters Theses

Keywords and Phrases

Gamma titanium aluminide

Abstract

"A powder metallurgy route based on hot isostatic pressing (HIPing) of tape-cast monotapes was investigated for the direct fabrication of dense thin sheets of gamma titanium aluminide (γ-TiAl). Sheets of γ-TiAl can be produced by rolling cast ingots or powder metallurgy plates but the process requires considerable thermomechanical treatment, making it expensive. In the present work, γ-TiAl powder was tape-cast to form a sheet (thickness = 500-700 μm). Insertion of the tape-cast sheet into a HIP can, binder removal in situ by thermal decomposition, HIPing for 15 min at 1100°C and 130 MPa, and decanning by a dissolution and oxidation process produced a dense sheet with a thickness of 250-300 μm. The research involved process optimization, chemical analysis, hardness testing, microstructural analysis, and microstructural manipulation by thermal annealing. The carbon content in the dense sheet was 0.13 wt.%, which was only 0.035 wt.% higher than that of the starting powder, but the oxygen content (0.44 wt.%) was significantly higher, presumably introduced during the oxidation stage of decanning. The hardness measured using Vickers microindentation technique was 384 ± 9 HV. Polarized light microscopy revealed that the dense sheet consisted of a fine-grained microstructure (average grain size ~ 3 μm) but also contains a few isolated larger grains (~ 20 μm). Microstructure analysis showed that the primarily metastable microstructure of the rapidly solidified starting powder transformed to the equilibrium near-γ microstructure during HIPing. The fine-grained microstructure of the HIPed sheet seems to have resulted from the fine, uniform structure of the atomized powder. Thermal annealing at 1175 and 1250°C for up to 1 hour, in flowing argon, produced limited grain growth but no discernable change in the near-γ microstructure. As-HIPed sheets heated to 1325 and 1375°C had a duplex microstructure with lamellar grains (~ 25 μm) near the surface. The surface effects were likely caused by oxidation. Removal of the oxidized surface layer (~ 25-50 μm thick) is likely to result in a sheet with uniform microstructure"--Abstract, page iii.

Advisor(s)

Rahaman, M. N., 1950-

Committee Member(s)

Van Aken, David C.
Mishra, Rajiv S.
Dutton, Rollie E.

Department(s)

Materials Science and Engineering

Degree Name

M.S. in Ceramic Engineering

Comments

This work was funded by TOPS DO Contract Number 0032 with the Air Force Research Laboratory, Materials and Manufacturing Directorate, Wright-Patterson Air Force Base, OH.

Publisher

University of Missouri--Rolla

Publication Date

Spring 2005

Pagination

x, 64 pages

Note about bibliography

Includes bibliographical references (pages 60-63).

Rights

© 2005 Alicia Gayle Adams, All rights reserved.

Document Type

Thesis - Restricted Access

File Type

text

Language

English

Subject Headings

Titanium alloys -- Heat treatmentIsostatic pressingSlip casting

Thesis Number

T 8780

Print OCLC #

62783780

Electronic OCLC #

1089948249

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