Uniaxial stress dependence of the [[zeta][zeta]0]-TA[sub 2] phonon branch in Ni[sub 60]Al[sub 40]
- Brookhaven National Lab., Upton, NY (United States). Dept. of Physics
There have been extensive experimental and theoretical studies of martensite transformations (MT) in metallic alloys. Much of the work has concentrated on precursor or premartensite effects prior to the actual phase transformation. Although the understanding has not yet converged, it is generally agreed that the strain fluctuations in the parent lattice are crucial for the occurrence of a MT. Many studies have focused on Ni[sub x]Al[sub 1[minus]x] alloys, which undergo a MT for 60 < x < 64 from a CsCl structure parent ([beta]) phase to a low temperature martensite phase at transition temperature T[sub M]. For T > T[sub M], a strongly temperature dependent phonon anomaly and temperature dependent diffuse scattering are observed by neutron scattering. In Ni[sub 62.5]Al[sub 37.5], an anomaly exists in the [[zeta][zeta]0]-TA[sub 2] phonon branch at [zeta] ca 1/6 which becomes more pronounced as the temperature is reduced toward T[sub M] ca 85 K. At the same [zeta] value, an elastic diffuse central peak is found near room temperature, whose intensity increases as temperature decreases, and reaches a maximum around T[sub M]. Below T[sub M], a new 7M martensite structure appears with Bragg peaks occurring near [zeta] = 1/7. Studies of precursor phenomena in Ni[sub 62.5]Al[sub 37.5] have demonstrated that applying uniaxial stress on Ni[sub x]Al[sub 1[minus]x] alloys could trigger'' a MT at higher temperature due to the martensite nucleation processes. In Ni[sub 62.5]Al[sub 37.5], the martensite transition temperature increases linearly from 85--300 K when a uniaxial stress was applied from 0--150 MPa. For x = 60 no MT occurs. This seems to be near the lower limit of composition where a MT occurs. The authors explore the possibility of inducing a MT in Ni[sub 60]Al[sub 40] by applying a uniaxial stress. They focus on the uniaxial stress dependence of the [[zeta][zeta]0]-TA[sub 2] phonon mode and the associated elastic diffuse scattering as a function of applied stresses.
- DOE Contract Number:
- AC02-76CH00016
- OSTI ID:
- 7289478
- Journal Information:
- Scripta Metallurgica et Materialia; (United States), Vol. 31:2; ISSN 0956-716X
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
ALUMINIUM ALLOYS
CRYSTAL-PHASE TRANSFORMATIONS
NICKEL BASE ALLOYS
CRYSTAL LATTICES
INELASTIC SCATTERING
MEASURING METHODS
NEUTRONS
PHONONS
TEMPERATURE DEPENDENCE
ALLOYS
BARYONS
CRYSTAL STRUCTURE
ELEMENTARY PARTICLES
FERMIONS
HADRONS
NICKEL ALLOYS
NUCLEONS
PHASE TRANSFORMATIONS
QUASI PARTICLES
SCATTERING
360102* - Metals & Alloys- Structure & Phase Studies