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We have measured the adiabatic elastic constants of two Cu-Al-Ni martensitic alloys using ultrasonic methods and we have compared the results to recent neutron-scattering experiments. It is shown that the elastic behavior of Cu-Al-Ni alloys follows the same trends exhibited by other Cu-based alloys; in particular, the TA2 long-wavelength acoustic modes are softer than all other modes.

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Brief Reports are accounts of completed research which, while meeting the usual Physical Review standards of scientific quality, do not warrant regular articles A. Brief Report may be no longer than four printed pages and must be accompanied by an abstract. The same publication schedule as for regular articles is followed, and page proofs are sent to authors To quantify the vibrational anharmonicity of the long-wavelength acoustic modes of bcc Cu74 ]A123 )Be& 8 near its martensitic transition temperature M, (261 K), the hydrostatic pressure derivatives (BC»/BP)p =0 of the elastic stiffness moduli have been measured. The Griineisen parameters at 268 K (just above M, ), especially of longitudinal modes, which become smaller than those of the shear modes, are quite different from those at 295 K: the anharmonicity changes markedly in the vicinity of the transition. Similar trends are noted for Cu«&A112 7Zn, o 8. Experimental data near M, are used to estimate cubic invariants in the strain order parameters in a Landau formalism.Many metals, including bcc Cu-based alloys, undergo a first-order martensitic transition from a high-temperature bcc phase to a close-packed structure on lowering the temperature.