Electron microscopy and neutron scattering studies of premartensitic behavior in ordered Ni-Al US 2 phase
High-resolution electron microscopy and elastic and inelastic neutron scattering examinations of the US 2 (B2) phase of Ni/sub 62. 5/Al/sub 37.5/ show a direct relationship between the evolution of premartensitic structural configurations and anamalous changes in lattice dynamical behavior as the US 2 cools toward its martensitic transformation temperature, M/sub s/. The resulting microstructure is a fine-scale mosaic assembly of nonuniformly distorted and modulated domains, in which /l brace/110/r brace/<110> shear-plus-shuffle displacements five rise to the /l brace/110/r brace/B2 micromodulations of /approximately/1.3 nm wavelength. These displacements are derived from the unusually low energy of the 4 /minus/ TA2 phonon mode and its anomalous temperature-dependent incomplete softening at /zeta/ = O (viz., the elastic constant C') and at /zeta/ approx. 0.16. The domains (''dressed embryos'' in Yamada's terminology) are viewed as the precursors to nucleation of the product 7R(52) martensite; the way this transformation process is facilitated, however, is still a problem to be solved. 36 refs., 6 figs.
- Research Organization:
- Brookhaven National Lab., Upton, NY (USA)
- DOE Contract Number:
- AC02-76CH00016; W-7405-ENG-48
- OSTI ID:
- 6479051
- Report Number(s):
- BNL-41957; CONF-880529-8; ON: DE89005645
- Resource Relation:
- Conference: MRS international meeting on advanced materials, Tokyo, Japan, 30 May 1988; Other Information: Portions of this document are illegible in microfiche products
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
SUPERCONDUCTIVITY AND SUPERFLUIDITY
36 MATERIALS SCIENCE
NICKEL BASE ALLOYS
PHASE TRANSFORMATIONS
ALUMINIUM ALLOYS
CRYSTAL STRUCTURE
ELASTIC SCATTERING
ELECTRON MICROSCOPY
INELASTIC SCATTERING
MARTENSITE
MICROSTRUCTURE
NEUTRON DIFFRACTION
TEMPERATURE DEPENDENCE
ALLOYS
CARBON ADDITIONS
COHERENT SCATTERING
DIFFRACTION
IRON ALLOYS
MICROSCOPY
NICKEL ALLOYS
SCATTERING
656002* - Condensed Matter Physics- General Techniques in Condensed Matter- (1987-)
360102 - Metals & Alloys- Structure & Phase Studies