Further Improvement of Shape Memory Effect in a Co-6.8Al-6.3W Alloy Through Aligned Precipitates

To confirm the feasibility that the shape memory effect (SME) in the Co-Al-based alloys undergoing fcc reversible arrow 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-6.3Walloy and their resulting precipitation behavior during aging. The results showed that the aligned beta-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 beta-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. (C) 2020 Elsevier B.V. All rights reserved.