Atomic structure of interphase boundary enclosing bcc precipitate formed in fcc matrix in a Ni-Cr alloy

Journal Article · Tue Aug 01 04:00:00 EDT 1995 · Metallurgical Transactions, A

DOI:https://doi.org/10.1007/BF02670668· OSTI ID:109777

Furuhara, T; Wada, K; Maki, T ^[1]

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1. Kyoto Univ. (Japan)

The atomic structure of the interphase boundary enclosing body-centered cubic (bcc) lath-shape precipitates formed in the face-centered cubic (fcc) matrix of a Ni-45 mass pct Cr alloy was examined by means of conventional and high-resolution transmission electron microscopy (HRTEM). Growth ledges were observed on the broad faces of the laths. The growth ledge terrace (with the macroscopic habit plane {approximately}(112){sub fcc}//(23{bar 1}){sub bcc}) contains a regular array of structural ledges whose terrace is formed by the (111){sub fcc}//(110){sub bcc} planes. A structural ledge has an effective Burgers vector corresponding to an a/12[1{bar 2}1]{sub fcc} transformation dislocation in the fcc {yields} bcc transformation. The side facet (and presumably the growth ledge riser) of the bcc lath contains two distinct types of lattice dislocation accommodating transformation strains. One type is glissile dislocations, which exist on every six layers of parallel close-packed planes. These perfectly accommodate the shear strain caused by the stacking sequence change from fcc to bcc. The second set is sessile misfit dislocations ({approximately}10 nm apart) whose Burgers vector is a/3[111]{sub fcc} = a/2[110]{sub bcc}. These perfectly accommodate the dilatational strain along the direction normal to the parallel close-packed planes. These results demonstrate that the interphase boundaries enclosing the laths are all semicoherent. Nucleation and migration of growth ledges, which are controlled by diffusion of substitutional solute atoms, result in the virtual displacement of transformation dislocations accompanying the climb of sessile misfit dislocations and the glide of glissile dislocations simultaneously. Such a growth mode assures the retention of atomic site correspondence across the growing interface.

• OSTI ID: 109777
• Journal Information: Metallurgical Transactions, A, Journal Name: Metallurgical Transactions, A Journal Issue: 8 Vol. 26; ISSN 0360-2133; ISSN MTTABN
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
BURGERS VECTOR
CHROMIUM ALLOYS
CRYSTAL STRUCTURE
DIFFUSION
DISLOCATIONS
INTERFACES
INTERMETALLIC COMPOUNDS
MICROSTRUCTURE
NICKEL ALLOYS
NUCLEATION
PRECIPITATION
STRAINS
TRANSMISSION ELECTRON MICROSCOPY