The effects of thermal aging in Cu-Al-Ni and Cu-Al-Be shape memory alloys

The metastable ß-phases of shape memory alloys are very sensitive to the effects of thermal aging before and after transformation. These thermal behaviours cause to considerable variations on the stability of austenite and martensite phase, the morphological structure of alloys, transformation temperatures hardness and the other transformation parameters.In this study, the effect of thermal aging on Cu-11.6 Al-0.42 Be, Cu- 13.5 Al-4 Ni vand Cu-13.0 Al- 4 Ni alloys were investigated by using differantial scanning calorimetry (DSC), X-ray piece diffraction, measurement of micro hardness and metallographic observations.The transformation temperatures, lattice parameters and hardness of the aged samples, which were aged nearly 50 °C above the austenite finish temperature of samples, cooled from ß-phase region. Besides this, it was investigated that there are variations in enthalpy and entropy.In microscopic investigation, martensite structures, self-accommodating martensite plates groups and precipitate phases were found.KeyWords: CuAlBe and CuAlNi shape memory alloys, martensitic transformation, aging effects,transformation temperatures, vickers hardness.