The Formation of Dispersions of Rare Earth Oxides in Titanium Alloys Using Rapid Solidification Processing
Konitzer, Douglas Gerard
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https://hdl.handle.net/2142/71811
Description
Title
The Formation of Dispersions of Rare Earth Oxides in Titanium Alloys Using Rapid Solidification Processing
Author(s)
Konitzer, Douglas Gerard
Issue Date
1984
Department of Study
Metallurgy and Mining Engineering
Discipline
Metallurgical Engineering
Degree Granting Institution
University of Illinois at Urbana-Champaign
Degree Name
Ph.D.
Degree Level
Dissertation
Keyword(s)
Engineering, Metallurgy
Abstract
Rapid solidification processing (RSP) has been used to produce extended solid solutions of rare earth elements and O in Ti, and some of its alloys. RSP has been effected by laser surface melting and the resulting microstructures have been characterized using the various techniques associated with analytical transmission electron microscopy. Heat treatment, typically 10 h at (TURN)1000 K results in the formation of an ultrafine dispersion of rare earth oxides. In the case of Er(,2)O(,3), the particles are (TURN)8.20 nm in diameter with a mean interparticle spacing of 120 nm. Considerable effort has been placed on the unambiguous identification of these small second phase particles. Convergent beam electron diffraction has been used to determine the point and space groups of these precipitates and the results are consistent with these being m3 and Ia3, respectively, which are identical with those of the rare earth oxides Y(,2)O(,3), Er(,2)O(,3). The orientation relationships (OR) exhibited by these oxide particles have been studied. Two such OR's are observed; the first is described by
An analysis of the sharing of symmetry between the second phase and matrix according to the first OR leads to the deduction that the intersection group is (')3, and this is consistent with the shape, hexagonal prisms, adopted by these particles. The second OR does not lend itself so easily to such an analysis; here the intersection is (')1, and the expected shape is a pinacoid (platelet). The reasons for this are discussed.
The coarsening equations have been modified for the special case of Er(,2)O(,3) particles in a Ti matrix. The resulting forms have been used to predict the coarsening behavior of the dispersions produced in this work. It is found that two cases must be considered. First, if the composition of the alloy contains an excess amount of Er, the particles exhibit remarkable stability up to the (beta)-transus. Above this temperature, the coarsening rate increases markedly. The second case involves a slight excess of O, and it is found that the stability of the particles is extremely improved up to temperatures in excess of (TURN)1200 K. These predictions have been verified by experiment.
Some preliminary measurements of the improvement in mechanical properties have been made. In a specimen tested for failure, it was found that there was a marked increase in mechanical strength.
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