Invariant line strain and needle-precipitate growth directions in Fe-Cu
A detailed theory of precipitate needle growth based on the invariant line hypothesis is presented for f.c.c. and b.c.c. alloy systems. The basic concept that coherent needle axes lie on cones of unextended lines is applied to semicoherent needles and it is shown that loss of coherency and growth is possible only for those needles lying at the intersection of a cone of unextended lines with a matrix slip plane. For these needles shear dislocation loops can relieve the coherency stresses. Owing to the different slip geometries (561) needle directions clustered around (110) directions are predicted for b.c.c. Cr precipitate needles in an f.c.c. Cu matrix and (557) and (656) directions clustered around (111) for the inverse case of f.c.c. Cu in b.c.c. Fe. Precise experimental measurements on both the alloy systems are in excellent agreement with the predictions. Differences observed in the incidence of (557) and (656) needles in Fe-Cu are related to the relative efficiency of the available matrix slip systems in providing transformation strain relief. It is concluded that the two factors that govern the precipitate crystallography are strain minimization and crystallographic strain relief.
- Research Organization:
- Materials and Molecular Research Division, Lawrence Berkeley Laboratory, University of California, Berkeley, CA
- OSTI ID:
- 5038558
- Journal Information:
- Acta Metall.; (United States), Journal Name: Acta Metall.; (United States) Vol. 32:5; ISSN AMETA
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
360102* -- Metals & Alloys-- Structure & Phase Studies
ALLOY SYSTEMS
ALLOYS
BCC LATTICES
BINARY ALLOY SYSTEMS
COPPER ALLOYS
CRYSTAL DEFECTS
CRYSTAL GROWTH
CRYSTAL LATTICES
CRYSTAL STRUCTURE
CRYSTAL-PHASE TRANSFORMATIONS
CRYSTALLOGRAPHY
CUBIC LATTICES
DISLOCATIONS
FCC LATTICES
IRON ALLOYS
LINE DEFECTS
METALLURGY
PHASE TRANSFORMATIONS
PHYSICAL METALLURGY
SHEAR
SLIP
STRAINS
STRESSES