University of Illinois Urbana-Champaign

An in-situ x-ray diffraction study of decomposition kinetics in a nickel-12.5 at.\% aluminum alloy

Marsh, Charles P.

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https://hdl.handle.net/2142/22509

Description

Title
An in-situ x-ray diffraction study of decomposition kinetics in a nickel-12.5 at.\% aluminum alloy
Author(s)
Marsh, Charles P.
Issue Date
1989
Department of Study
  • Engineering, Metallurgy
  • Engineering, Materials Science
Discipline
  • Engineering, Metallurgy
  • Engineering, Materials Science
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
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.
Type of Resource
text
Permalink
http://hdl.handle.net/2142/22509
Copyright and License Information
Copyright 1989 Marsh, Charles P.

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