MARTENSITIC TRANSFORMATION AND METALLURGICAL STUDY OF LOW TEMPERATURE Cu-Al-Be TERNARY ALLOY

Abstract

Abstract:The present study on a Cu-Al-Be alloy has given the following characteristics: the addition of small concentration of beryllium to the eutectoidal alloy close to Cu3Al leads to a sharp decrease of the martensitic transformation temperatures. At the same time the composition corresponding to the maximum stability of the beta phase does not change significantly. The eutectoidal temperature is lowered, but the temperature of beta solution treatment remains the same. Moreover there is no change in the nature of the martensitic transformation (DO3 t ,

Aging behavior in Cu–Al–Be shape memory alloy

“…[4][5][6] Among Cu-based shape memory alloys, Cu-Al-Be is the one that has been developed more recently and is unique because of its adaptability for high as well as low temperature actuator applications. 7 Indeed, this potentiality is the result of the drastic effect of a small addition of Be to the Cu-Al system, which strongly reduces the martensitic transition temperature and leaves practically unaltered the low temperature limit of stability of the ␤ phase ͑eutectoid point͒, as well as the order-disorder transition line. 6,7 Above room temperature, aging effects represent a serious limitation on the actual applications of shape memory alloys.…”

“…7 Indeed, this potentiality is the result of the drastic effect of a small addition of Be to the Cu-Al system, which strongly reduces the martensitic transition temperature and leaves practically unaltered the low temperature limit of stability of the ␤ phase ͑eutectoid point͒, as well as the order-disorder transition line. 6,7 Above room temperature, aging effects represent a serious limitation on the actual applications of shape memory alloys. 8 In several Cu-based alloys, such as the Cu-Zn-Al and Cu-Al-Ni systems, these effects have been extensively studied and are well understood in terms of ordering processes.…”

Low-lying phonon dispersion curves ofD03Cu3Mañosa1, Zarestky2, Bullock3 et al. 1999Phys. Rev. B

“…The conventional unit cell contains eight bcc cells and the lattice parameter is doubled. The addition of a small amount of beryllium to the stoichiometric Cu 3 Al does not modify significantly the position of the eutectoid point in the equilibrium phase diagram, 5 and the order-disorder transition temperature of this ternary alloy is only weakly dependent on the Be. As we already pointed out, on the other hand, the martensitic transition temperature is very sensitive to the Be concentration.…”

What Determines the Martensitic Transition Temperature in Alloys ?

“…The effect is much larger than conceivable from estimated consequences of changes in the electronic effects, in the inter ato111ic forces, in atomic radii or as a result of atomic ordering. In the complicated alloys, as for example Ni,Til-, [I] and CusAIBe, [2] a dramatic change in Ms is observed for x = 0.5 and E c 0. In these interesting systems probably all the mentioned effects play a role, but still it is hard to understand the strong influence on M,.…”