Texture development and transformation strain of a cold-rolled Ti50-Ni45-Cu5 alloy

Shape memory alloys (SMAs) are finding increased use as functional materials in the aerospace, energy and medical industries 1 J. van Humbeeck, Shape Memory Materials and Phenomena—Fundamental Aspects and Applications, p. 3771, vol. 246, MRS, Pittsburgh, PA (1992).(1), (2) and (3). Shape memory behaviour is based on the recovery of large amounts of induced strain upon heating and/or unloading. This transformation strain is a result of the reversible growth of certain favoured martensite variants during martensite transformation and/or stressing [4] and [5]. For single crystal SMAs, the favoured variants are those which result in the maximum transformation strain for a specific orientation. This has been well established for several common single crystal SMAs such as TiNi, CuZnAl and CuAlNi [4] and [6]. For polycrystalline SMAs, it is not clear which variants are favoured. Anisotropic behaviour in SMAs has been interpreted based on the anisotropy data of single crystal materials using the concept of the selection of favoured martensite variants. This has met with only limited success in work on NiTi alloys due to the lack of information about which variants are formed [7] and [8]. An investigation of the anisotropic behaviour of textured SMAs was thus conducted in order to determine which martensite variants develop during thermal cycling of a commercial TiNiCu SMA. The relationship between the observed variant development, changes in texture and anisotropic shape memory behaviour are discussed in light of models using the concept of favoured martensite variants.