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Title

MESOSCALE DEFORMATION IN A 9310 STEEL AND 2139 ALUMINUM ALLOY

Creator

Snyder, David

Date

2012-09-10, 2012-12

Description

As technology continues to develop, the need for materials with superior structural performance grows. In recent years, the design of such...
Show moreAs technology continues to develop, the need for materials with superior structural performance grows. In recent years, the design of such high integrity alloys has led to a need for a more fundamental understanding of the deformation response of materials under various loading conditions. In this study, the deformation response of two high performance, high stacking fault metallic alloys are investigated. It has long been known that deformation in high stacking fault metals is a complex process of dislocation interactions that vary substantially with the loading conditions of strain, strain rate and temperature, as well as the chemistry and processing history of the alloy. The flow behavior and recrystallization response of a 9310 steel alloy deformed in the ferrite temperature range were studied in this work. Samples were compressed under various conditions of strain, strain rate and temperature using a Gleeble thermo-mechanical simulator. Deformation was characterized by both qualitative and quantitative means, using standard microscopy, electron backscatter diffraction (EBSD) analysis and flow stress modeling. The results indicate that deformation is primarily accommodated through dynamic recovery in sub-grain formation. EBSD analysis shows a continuous increase in sub-grain boundary misorientation with increasing strain, ultimately producing recrystallized grains from the sub-grains at high strains. This suggests that a sub-grain rotation recrystallization mechanism predominates in this temperature range. Demonstrated trends include a decreasing mean dynamically recrystallized grain size with increasing strain and Zener-Hollomon parameter, and an increasing recrystallized fraction with increasing strain. Another high stacking fault metal that has garnered a great deal of attention for its possible high performance structural applications is the 2139 aluminum alloy. In this study, the effect of chemistry and strain on the deformation response of the alloy system is investigated. 2139 aluminum is a very complex alloy, with multiple strengthening phases and mechanisms contributing to its overall high structural integrity compared to other aluminum alloys in its class. While the structural performance and TEM-scale deformation behavior of this alloy have been extensively analyzed, grain-scale microstructural features of deformation have not been well characterized. In addition, the contributions of each strengthening mechanism in the alloy are not well established. To characterize the deformation response of the alloy, alloys of various chemistries were produced and subjected to room temperature compression testing, in order to isolate and establish the effects of the major strengthening mechanisms on the overall behavior. Through electron backscatter diffraction analysis, the microstructural features of deformation generated in the alloys under these conditions were characterized, and the evolution and distribution of strain on a grain-scale was analyzed. Differences in deformation behavior with alloy chemistry were established by tracking differences in the evolution of lattice rotations with strain in the several alloys. It was determined that, for alloys subjected to artificial aging, the refinement in scale and distribution of the precipitate structure represents the greatest decrease in the development of lattice rotations with strain. This represents a first study into the room temperature, grain-scale deformation response of a heavily alloyed aluminum alloy, and the effect of alloy chemistry and precipitate structure on the deformation behavior of a 2139 aluminum alloy. As a preface to this study, a thorough review of the current state of literature on the deformation response of aluminum alloys was compiled as well.
M.S. in Materials Science and Engineering, December 2012
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