Masters Theses

Abstract

"Two titanium alloys have been characterized using transmission and scanning electron microscopy, X-ray diffraction, and optical metallography techniques. Both of these alloys were rapidly solidified by melt spinning, the resulting ribbons pulverized, and the powders then extruded into cylindrical billets. The alloys are based on the compositions Ti-21.3Al- 9 Nb-0.6-Mo-2.6V and Ti-13.2Al-2.6Nb-0.5Mo-0.9V-0.5Zr-3.1B in atomic percent. The first alloy was examined in both the as-extruded condition and in the annealed condition (looo0c for 12 hours). The second alloy was examined in the as-extruded condition only.

For the first alloy, the as-extruded microstructure consisted of a B2 matrix with alpha-2 particles at the grain boundaries; the orthorhombic phase was found only at the periphery of the alpha-2 particles. The B2 phase had begun to decompose to the equilibrium alpha-2. Small acicular precipitates in the interior of the B2 grains were identified as alpha-2. Annealing produced a microstructure of primary alpha-2 and alpha-2/beta in a Widmanstatten structure. The Nb, V, and Mo, all beta-stabilizing elements, partitioned to the B2 phase in the as-extruded specimen, while the Widmanstatten structure contained a significantly larger fraction of the three elements. The alpha-2 composition changed very little between the as-extruded and annealed specimens. The texture in the B2/beta phase consisted of {110} planes aligned perpendicular to the extrusion axis, with a cylindrical texture also present consisting of the {211} and {200} planes. The alpha-2 texture consisted mainly of the {0002} planes aligned perpendicular to the extrusion axis.

The second alloy was found to contain a possible metastable Ti2B phase. Electron diffraction was used to identify the borides, which were present in two different size distributions. Calculated patterns were used to help distinguish between Ti2B and the more common orthorhombic TiB. The boride particles are thought to have formed in the melt and by a solid-state precipitation reaction"--Abstract p. iv

Advisor(s)

Joseph William Newkirk

Committee Member(s)

Donald R. Askeland
Richard D. Hagni

Department(s)

Materials Science and Engineering

Degree Name

M.S. in Metallurgical Engineering

Publisher

University of Missouri--Rolla

Publication Date

Spring 1990

Pagination

xii, 85 pages

Note about bibliography

includes bibliographical references (pages 83-84)

Rights

© 1990 Danny Joe Edwards, All rights reserved.

Document Type

Thesis - Open Access

File Type

text

Language

English

Thesis Number

T 6008

Print OCLC #

22426493

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