A COMPARATIVE-STUDY OF THE POST-QUENCH BEHAVIOR OF CU-AL-BE AND CU-ZN-AL SHAPE-MEMORY ALLOYS

This paper reports a comparative investigation of the effect of quench ing on the Cu-Al-Be and Cu-Zn-Al shape memory alloys by the use of sev eral experimental techniques. In a first stage, the order-disorder tra nsitions in these alloys have been characterized by means of modulated calorimetry. Results have proved that the A2 reversible arrow DO3 tra nsition in Cu-Al-Be is first order with a latent heat of 1160 J/mol; t he B2 reversible arrow L2(1) transition in Cu-Zn-Al is second order, a nd a peak in the specific-heal vs temperature curve has been observed. Secondly, the post-quench behaviour of these alloys, when subjected t o some of the typical heat treatments used to stabilize the beta phase , has also been studied by means of neutron diffraction, positron anni hilation and highly sensitive calorimetry. A different post-quench tim e evolution of the martensitic transition temperatures has been found for the two alloys. For Cu-Al-Be: this evolution has been shown to be correlated with positron annihilation data, while, for Cu-Zn-Al; a cor relation with neutron diffraction data has been established. These res ults show that the measured shifts in the transition temperatures indu ced by a quench are mostly due to an excess of vacancies in the case o f Cu-Al-Be, and to an incomplete degree of L2(1) atomic order in Cu-Zn -Al. (C) 1998 Acta Metallurgica Inc.