Alloy Plate

Alloy Plate made from the shape-memory and superelastic alloy Nitinol, a roughly equiatomic alloy of Ni and Ti, employs numerous processing techniques, e.g. tube drawing, plate rolling, etc., and heat treatment processes in order to modify the microstructure, transformation temperatures, and mechanical properties.  These procedures can lead to texturing (crystallographic alignment) of the material.  There are a few, mainly qualitative, reports of textures in Nitinol sheets and plates1-8 but no information for textures of tubes.  Since Nitinol derives its unique nonlinear and anisotropic mechanical behavior from stress-induced martensitic transformations, where the resulting strains are affected by crystallographic orientation, it is clear that texture can have a marked influence on its mechanical properties.  Indeed, Gall and Sehitoglu9 have concluded that texture, and consequently variants of martensite active during the transformation, are the source of the compression-tension asymmetry of Nitinol.  Furthermore, Vaidyanathan et al. 10 have concluded that texturing can occur in Nitinol when martensite is stress-induced from austenite via such compression loading.  Texture can have a critical effect in modeling the constitutive behavior of the alloy, as shown in Figure 111 where the assumption of the correct texture is shown to markedly influence the finite-element predictions of the equivalent stress-equivalent strain curve for Nitinol under combined tensile and torsional loading and unloading.