Further improvement of shape memory effect in a Co-6.8Al-6.3W alloy through aligned precipitates

Abstract To confirm the feasibility that the shape memory effect (SME) in the Co–Al-based alloys undergoing fcc⇌hcp martensitic transformation can be further improved by aligned precipitates, we investigated the intrusion of defects by high-temperature quenching or pre-deformation in a Co-6.8Al-6.3W alloy and their resulting precipitation behavior during aging. The results showed that the aligned β-CoAl precipitates could be induced after aging at 1073–1273 K in both the alloy water-quenched from 1523 K and the air-cooled alloy subjected to 5% pre-deformation at room temperature. The further SME enhancement was realized in both aged alloys containing many aligned precipitates. A high recovery strain of 4.3% was obtained in the water-quenched alloy aged at 1073 K. The directional stacking faults produced by water-quenching and the directional fcc/hcp phase interfaces produced by pre-deformation were responsible for the aligned β-CoAl precipitates. Moreover, a better SME was obtained in the water-quenched Co-6.8Al-6.3W alloy than in the air-cooled alloy because much more stacking faults were produced after water-quenching.