Date of Award
Electrical and Computer Engineering
Engineering, Materials Science.
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The study of the effect of Be on precipitation in Al-3%Cu alloy is focussed on the clustering process, GP zone formation, and the (theta)' (--->) (theta) transformation. An accelerated hardening is observed in the Al-3%Cu-0.1%Be alloy (weight percent) as compared to Al-3%Cu, when aged at room temperature and at 110(DEGREES)C. TEM analysis shows that GP zones are not present in Al-3%Cu-0.1%Be alloy aged to the hardness plateau, indicating that the faster hardening is not due to GP zone formation. A clustering process, in which clusters of Cu and Be atoms with vacancies are formed around dislocation lines, is proposed to explain the delay in GP zone formation and the observed rapid hardening. The (theta)' and (theta) precipitation in the alloys is investigated using a resistivity technique, and the precipitation can be described by Avrami type equation. Similar activation energies and 'n' constants indicate that the addition of Be does not alter the growth mechanism of (theta)' and (theta). A faster and earlier (theta)' (--->) (theta) transition in Al-3%Cu-0.1%Be alloy is established using both TEM and resistivity techniques. The higher 'k' values of the Avrami equation and the larger (theta) particle density observed initially in Al-3%Cu-0.1%Be alloy, suggest that Be increases the nucleation rate of (theta) phase. Strain energy for the formation of incoherent (theta) precipitate was calculated and found to be higher when Be is incorporated in the (theta) phase. The nucleation entropy of (theta) was estimated using the appropriate sequence of reactions. For (theta) phase with Be, substantially larger (absolute) entropy change was obtained, indicating that the observed higher nucleation rate of (theta) phase (with Be) is in agreement with the nucleation entropy theory.Dept. of Electrical and Computer Engineering. Paper copy at Leddy Library: Theses & Major Papers - Basement, West Bldg. / Call Number: Thesis1986 .K376. Source: Dissertation Abstracts International, Volume: 47-05, Section: B, page: 2111. Thesis (Ph.D.)--University of Windsor (Canada), 1986.
KAROV, J., "ROLE OF NUCLEATION ENTROPY IN PRECIPITATION IN ALUMINUM-COPPER ALLOY." (1986). Electronic Theses and Dissertations. 3364.