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Formation and Morphology of Kurnakov Type D022 Compound in Disordered fcc γ-(Ni, Fe) Matrix Alloys
Published online by Cambridge University Press: 26 February 2011
Abstract
Formation and morphology of D022 compound Ni3V in γ-fcc alloys were investigated as a model case in order to understand fundamentals for microstructure control of new class of austenitic steels strengthened by Kurnakov-type GCP intermetallic compound. The formation process of the D022 phase in γ matrix varies, depending on the composition and heat treatment temperature, and precipitation of D022 takes place at temperature above T0 in the γ+D022 two phase region. The morphology of coherent precipitates of the D022 compound is sensitive to misfit strains against matrix and can be controlled by alloying addition. The habit planes between the two phases become irrational, parallel to both directions of the invariant line and an a-axis of D022, since the lattice misfit becomes negative along a-axis (δa) and positive along c-axis (δc) of the D022. The calculation based on the lattice invariant theory as well as experimental results clearly demonstrate that the misfit strain ratio δc/δa is a dominant factor to determine the habit plane. In addition, the shape of D022 phase, either prism or plate, depends strongly on the magnitude of |δa|. These findings will extend to Ni-Fe-Nb-V quaternary system, by partial replacement of Ni with Fe and that of V with Nb.
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- Copyright © Materials Research Society 2005