Cubic and hexagonal single-crystal elastic constants of a cobalt-nickel alloy

A cubic single crystal of cobalt-32-wt% nickel was transformed to a hexagonal single crystal by cooling a uniaxially prestressed specimen. Evidence that the transformed specimen is a hexagonal single crystal was obtained by Laue x-ray photographs, surface markings, analysis of the magnitude of sound-wave velocities and the symmetry of their polarizations, and the magnetic field dependence of the attenuation of certain modes. The complete sets of second-order and third-order elastic constants of both the cubic and hexagonal phases were measured. These constants were used to calculate the change in enthalpy upon transformation, and the stacking-fault energy. The results are in good agreement with available thermodynamic data.