Unusual reversible twinning modes and giant superelastic strains in FeNiCoAlNb single crystals

The superelastic response of the Fe41Ni28Co17Al11.5Nb2.5 (at. %) single crystals oriented along the [001] direction was investigated in tension at various temperatures after aging at 973 K for 0.5 h. The aging treatment led to the formation of ordered gamma' particles with particle sizes of less than 3 nm. Abnormally large reversible strain of up to 15.3% was observed at 77 K, the highest ever reported for an iron-based shape memory alloys. It has been revealed that this giant superelastic strain, significantly higher than the theoretical transformation strain, is associated with gamma-alpha' martensitic transformation and elastic mechanical twinning of < 011 >{110} type. (C) 2016 Elsevier Ltd. All rights reserved.