The plastic deformation of alloys based on aluminum titanide
Lofvander, Jan Per Axel
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Permalink
https://hdl.handle.net/2142/20756
Description
Title
The plastic deformation of alloys based on aluminum titanide
Author(s)
Lofvander, Jan Per Axel
Issue Date
1989
Doctoral Committee Chair(s)
Fraser, Hamish L.
Department of Study
Materials Science and Engineering
Discipline
Materials Engineering
Degree Granting Institution
University of Illinois at Urbana-Champaign
Degree Name
Ph.D.
Degree Level
Dissertation
Keyword(s)
Engineering, Metallurgy
Language
eng
Abstract
The thermal stability of a dispersion of rare-earth oxide particles in Ti and Ti$\sb3$Al matrices has been considered analytically and determined experimentally. The solubility product for the formation of erbia (Er$\sb2$O$\sb{3)}$ in a Ti matrix has been calculated using known thermodynamic data which allows the concentration terms in the Lifshitz, Slyozov and Wagner coarsening equation to be calculated. Predictions show that a dispersion will exhibit a greater thermal stability when in a matrix with an excess concentration of oxygen (with respect to that necessary to form the stoichiometric Er$\sb2$O$\sb3$) compared with an excess concentration of erbium. The diffusivity of Er in Ti$\sb3$Al has been approximated on the basis of known thermodynamic and elastic data. This result has been used to estimate the thermal stability of erbia in Ti$\sb3$Al. A model has been developed which describes accelerated Ostwald ripening at moving interfaces. Isothermal and isochronal annealing experiments have been executed on rapidly solidified materials with results which are consistent with the presented predictions.
Four different Ti$\sb3$Al alloys have been produced by centrifugal atomization, namely Ti$\sb3$Al 0.7Er, Ti$\sb3$Al 2.5Nb, Ti$\sb3$Al 5Nb and Ti$\sb3$Al 11Nb (at.%) which have been characterized in the as-rapidly solidified and consolidated (by HIP) condition. A previously unreported Ti-Er-O phase has been identified and characterized using SAD, EDS, EELS and AUGER microanalysis techniques.
The four alloys named above have been deformed in compression to $\approx$3% strain at room temperature and 650$\sp\circ$C, and the resulting deformation microstructures have been analyzed and the Burgers vector determined by TEM contrast experiments. Stereographic analyses have been used to completely characterize slip systems in the deformed material. These results have been interpreted on the basis of a model of anisotropic charge distribution around atoms in sheets containing only Ti atoms in Ti$\sb3$Al.
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