A non-invariant plane model for the interface in CuAlNi single crystal shape memory alloys

A non-invariant plane model for the austenite-martensitic (A-M) interface in CuAlNi single crystal shape memory alloys (SMAs) is proposed in this paper. The model is based on the crystallography of martensitic transformation and the recent uniaxial tensile Moire tests on Cu-14\%Al-4.12\%Ni (wt\%) single crystals, The two types of specimens used have the same tensile axis orientation but have different transition temperatures. One exhibits Shape Memory Effect (SME) and the other exhibits Superelasticity (SE). In the case of SME, the plane invariant nature of the A-M interface is well verified by the Moire test. On the contrary, the A-M interface in the case of SE was identified to be a non-invariant plane. A crystallography-based model is proposed to explain the formation of this non-plane-invariant A-M interface in SE and is used to predict the resultant interface structure and the transformation strain of the stress-induced beta(1)-->beta'(1) transformation in CuAlNi. The comparison between the theoretical calculations and the experimental results support the proposed model. (C) 2000 Elsevier Science Ltd. All rights reserved