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 Title: An in-situ x-ray diffraction study of decomposition kinetics in a nickel-12.5 at.\% aluminum alloy Author(s): Marsh, Charles P. Department / Program: Engineering, MetallurgyEngineering, Materials Science Discipline: Engineering, MetallurgyEngineering, Materials Science Degree Granting Institution: University of Illinois at Urbana-Champaign Degree: Ph.D. Genre: Dissertation Subject(s): Engineering, Metallurgy Engineering, Materials Science Abstract: An in-situ study of the phase decomposition or precipitation reaction of a supersaturated solid solution single crystal of Ni-12.5 at.% Al alloy was performed for moderately high temperatures. The superlattice peaks caused by the coarsening reaction of the Ni$\sb3$Al phase were continuously monitored over time using wide angle x-ray diffraction. The Sherrer formula was used to calculate the average particle size. Higher order peaks were checked for broadening caused by strain and no significant effect was found. The integrated intensity from the superlattice peaks was also measured and was related to the total volume fraction of the second phase as the microstructure evolved. Interpreting the data using the diffusion-controlled coarsening theory of Lifshitz and Slyozov, both the diffusion coefficient and the interfacial energy between the matrix and precipitates were experimentally determined for temperatures in the range of 550 to 700$\sp\circ$C. In addition, for two temperatures the coarsening rate was found to be different for two crystallographic directions. This difference is suggested to be related to the precipitate morphology change from sphere to cuboid evidenced in many Ni-base alloys. In addition the correlated arrangement of the precipitates was qualitatively measured by using small angle neutron scattering at different times during the decomposition and was found to be definitely present at the beginning of coarsening. It is also suggested that the 500$\sp\circ$C data of this work as well as the observed low temperature excess diffusion can be explained by an ordering process which occurs before the classical coarsening decomposition process becomes dominant. Issue Date: 1989 Type: Text Language: English URI: http://hdl.handle.net/2142/22509 Rights Information: Copyright 1989 Marsh, Charles P. Date Available in IDEALS: 2011-05-07 Identifier in Online Catalog: AAI9010951 OCLC Identifier: (UMI)AAI9010951
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