Neutron-scattering study of premartensitic behavior in Ni-Al alloys

Phonon dispersion curves for the 110 -110 TA2 branch in Ni(x)Al(100-x) x = 50-65 reveal a pronounced minimum whose position in q space is composition dependent but whose frequency does not change appreciably with temperature. In the same q range, substantial elastic scattering also appears which is associated with localized embryos of a low-temperature phase. The diffuse scattering from the elastic displacement field about these embryos is highly anisotropic, giving rise to the striated strain contrast (tweed) in the electron microscope image. A common electronic origin of these effects is proposed. (Author)