Grain boundary studies in ordered intermetallic compound Ni3 Al
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Theoretical and experimental studies of grain boundary structures were carried out to understand the grain boundary properties of Ni₃Al. Using various techniques of transmission electron microscopy, the geometry of grain boundaries was determined from a number of grain boundaries to obtain a distribution of grain boundary types in Ni₃Al. Five macroscopic parameters, including a misorientation between two grains and a grain boundary plane orientation, were considered in the grain boundary type. A distribution of grain boundary types in ductile Ni₃Al contained more low Σ boundaries than brittle Ni₃Al. In a distribution of grain boundary plane orientations, the trend of having high density plane of coincident sites was maintained on low Σ boundaries up to Σ = 9 and random orientations of grain boundary planes became dominant after Σ = 11. In ductile Ni₃Al, grain boundary accommodations of dislocations in the vicinity of grain boundaries were found, which were not shown in brittle Ni₃Al. Using CBED techniques, symmetry information of a single crystal was obtained. However, an extension to bicrystals was not successful. In order to study the possible disordering and segregation near grain boundaries, two different atomistic computer simulations, namely, molecular statics simulation and two dimensional lattice gas model, were carried out. Both results showed a similar trend of disordering near the grain boundary regardless of grain boundary composition and atomic interaction energy assumptions. However, segregation behavior near grain boundaries showed strong influences from grain boundary compositions and atomic interaction energy assumptions.
- Doctoral Dissertations