Shape memory alloys exhibit superelasticity when they are deformed in a temperature range where the thermoelastic martensite forms on application of a strain. The martensite persists upon removal of the applied strain, and the alloy recovers the original shape on heating over the reverse-transformation temperature after removing the strain. The -phase CuZnAl alloys have -type superlattice in the parent case, and M9R or M18R martensites occur on quenching the alloys from the homogenization temperature. The basal plane of martensite is exposed to hexagonal distortion with martensitic transformation as well as the monoclinic distortion in the crystal structure, and splittings are observed in some selected diffraction-peak pairs due to the differences in atom sizes in lattice points. These pairs have a great importance as ordering criteria and satisfy a special relation between Miller indices. The present text reports the variation of the differences in interplane spacings (⌬d ) between some selected planes upon the further aging at room temperature at which alloys are fully martensitic. The decrease of ⌬d during the aging implies that the monoclinic distortion decreases. The mass increases are caused by the oxidation upon heating the alloys at high temperatures close to the betatizing temperature at free atmosphere.
Macroscopic, structural and morphological features of shape memory CuZnAl alloys were examined by elongation parameter measurement, X-ray diffraction and optical metallography. It has been seen that shape initiating temperature (T z ) is greater than austenite start temperature (A s ). According to the X-ray diffraction, it has been defined that transformation happened from austenite phase to martensite phase as L2 1 → M 18R and martensite crystal lattice has been in monoclinic structure. In metallographic observations the grain structures were observed, then plate martensites, V-type martensite structures, twin-like bands, precipitation phases were found. In addition, it has been observed that α-sediment phase has occurred in specimens with ageing at austenitic phase condition.
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