Yield surfaces of shape memory alloys and their applications

The "yield" (transformation start stress in stress induced martensitic transformation) surfaces of shape memory alloys (SMAs) are investigated. It is assumed that the driving energy (or driving force) for phase transformation is approximately a constant. By using the lattice structure and correspondence of a SMA in phase transformation, the "yield" surfaces of the following polycrystalline SMAs are calculated: NiTi, NiAl, CuZnGa, and CuAlNi. It is also found that all these "yield" surfaces can be described roughly by a general formula. In this formula, the parameters can be decided by using the "yield" stresses of a particular SMA in uni-axial tension and compression. The "yield" surface of NiTi is compared with the experimental results reported in the literature. The possibility of applying such a "yield" surface in predicting the behavior of a SMA under other stress conditions based on the tensile result is also studied. (C) 1999 Acta Metallurgica Inc. Published by Elsevier Science Ltd. All rights reserved.