Thermomechanical Behaviour of Monocrystalline Cu-Al-Be Shape Memory Alloys and Determination of the Metastable Phase Diagram

Abstract

Stress-stain behaviour of monocrystalline Cu-Al-Be alloy was investigated by uniaxial tensile tests in a temperature range between -70 o C and +160 o C. Four kinds of typical behaviours were examined in this study. Main interest was the determination of the -T diagram obtained from the -e curves. This metastable phase diagram is comparable to the Cu-Al-Ni one. Isothermal mechanical cycling was made at 6% strain up to 1500 cycles. As a result, a deterioration of the superelastic behaviour was found. A thermal flash allows to partially recover this behaviour. Rupture tests performed at a temperature above 120 o C have shown the critical stress above which either brittle fracture of α' martensite occurs or plastic deformation of β phase takes place. Finally, comparative tests have been made between a single crystal, a polycrystal with small grains and a polycrystal with columnar structure (bamboo-type)