Deformation mechanisms in rapidly solidified aluminum alloys
Legzdina, Daira
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https://hdl.handle.net/2142/22045
Description
Title
Deformation mechanisms in rapidly solidified aluminum alloys
Author(s)
Legzdina, Daira
Issue Date
1989
Doctoral Committee Chair(s)
Fraser, Hamish L.
Department of Study
Materials Science and Engineering
Discipline
Metallurgical Engineering
Degree Granting Institution
University of Illinois at Urbana-Champaign
Degree Name
Ph.D.
Degree Level
Dissertation
Keyword(s)
Engineering, Metallurgy
Engineering, Materials Science
Language
eng
Abstract
The deformation mechanisms of four rapidly solidified (RS) and hot extruded aluminum alloys were investigated. Al-8.8Fe-3.7Ce (all compositions in wt%) and Al-8.9Fe-6.9Ce alloys produced from RS powders and two Al-8Fe-2Mo alloys one produced from RS ribbons and the other from powders, respectively, were creep tested in the temperature range 250$\sp\circ$C to 350$\sp\circ$C over a range of stresses from 15 to 250 MPa.
The Al-8.8Fe-3.7Ce alloy exhibited a diffusional creep region at low stresses and a power law creep region as the stress increased beyond a given transition stress. Coble creep was the deformation mechanism in the diffusional creep region and the strain rates were determined by the size of the RS particulate. In the power law region the creep rates could be predicted by the Sherby and Lin equation.
To investigate the influence of the thermal degradation on the creep behavior of the Al-Fe-Ce alloys both alloys were heat-treated for 165 hours at 450$\sp\circ$C, 500$\sp\circ$C and 550$\sp\circ$C, respectively, and creep tested at 300$\sp\circ$C. Both a diffusional and a power law region was observed for both alloys and all heat-treatment temperatures. An increase in the diffusional creep rates was observed for the heat-treated alloys instead of the expected decrease, confirming that the grain size of the material does not determine the creep rates in the diffusional creep region.
The Al-8Fe-2Mo ribbon extrusion exhibited a diffusional region at low stresses and a power law region at higher stresses. In the diffusional regime the strain rates were determined by the size of the RS particulate. When the data in the power law regime was plotted as normalized stress versus normalized strain, the Al-8Fe-2Mo data did not exhibit a single slope. The diffusional creep region was totally suppressed in the Al-8Fe-2Mo powder alloy, an observation that is in contrast with the behavior of all other alloys tested in this work. (Abstract shortened with permission of author.)
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