Elastic Behaviour in the β_1 Phase Region of Au_<52.5-x>Ag_xCd_<47.5> Thermoelastic Alloys

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A phase relation in Au _<52.5-x>Ag_xCd_<47.5> Pseudobinary alloys was studied, in which the transition temperatures of Heusler-type ordering and of thermoelastic martensitic transition were measured as a function of Ag content. It is of interest that (1) in the case of Heusler-ordering obtained by slow-cooling from the β_1 region, the To (=1/2(M_s+A_s) temperature gradually decreased with the increase of Ag content and exhibited a minimum at about 29 at% Ag, and then a maximum at about 35 at% Ag, and (2) in the case of CsCl-ordering. To showed a minimum at about 35 at% Ag and then a maximum at about 47 at% Ag. Temperature dependence of the elastic constants (ultrasonic velocities) and ultrasonic attenuations was measured by the ultrasonic pulse-echo method in the premartensitic temperature range near M_s by using single crystals. From these elastic constants data, the temperature dependence of the Debye characteristic temperature θ_T was calculated in the temperature range above M_s. Remarkable elastic softening and its large attenuation of C'=1/2(C_<11>-C_<12>), corresponding to the (110) [110]_<bcc> shear, were found in the temperature range fairly above M_s.
東北大学の論文