The influence of texture on the shape-memory effect in polycrystals

Abstract

AbstractÐA model is developed to show that texture is a crucial factor in determining the shape-memory e ect in polycrystals. In particular, it is established that texture is the reason why the strains recoverable in Ti±Ni are so much larger than those in Cu-based shape-memory alloys in rolled, extruded and drawn specimens. Further, it is shown that both these materials recover relatively small strains in sputter-deposited thin ®lms due to unfavorable texture. It is found that even the qualitative behavior of combined tension± torsion can critically depend on the texture. The results are in good agreement with experimental observations. Finally, textures are suggested for improved shape-memory e ect. #

Stress-Induced Phase Transformations in Shape-Memory Polycrystals

“…On the other hand, Bhattacharya and Kohn [4] had argued in the context of the shape-memory effect that the constant strain ansatz provides a reasonable indication of the extent of transformation. This was also shown to be consistent with diverse experimental observations [3,23] and numerical simulations [7]. Their idea roughly is that the poorly oriented grains saturate quickly to form a network that prevents further transformation.…”

Laser annealing of amorphous NiTi shape memory alloy thin films to locally induce shape memory properties

“…It is important to evaluate the crystallographic texture of laser annealed NiTi films because the recoverable strain depends on the texture of the films [18] and because strong textures may lead to anisotropic shape memory behavior [19,20], making the design and fabrication of actuators more challenging. A typical {110} pole figure measured by X-ray diffraction is shown in Fig.…”

Textural Evolution by Multiple Steps of Marforming in Ti-Rich Ni-Ti Shape Memory Alloy

“…Several studies are dedicated to understand the influence of the texture on thermomechanical response of the SMAs [8][9][10][11][12][13][14][15][16][17]. Thermal cycling and mechanical working are found to develop specific texture in metals and alloys.…”

“…The texture is found to give rise to anisotropy in transformation recovery strain [10]. NiTi SMA in austenitic field has a bcc type texture [13,14]: -fiber I <110>||RD ({001}<110>-{112}<110>-{111}<110>), -fiber II <110>||RD ({111}<110>-{110}<110>), fiber <111>||ND ({111}<110>-{111}<112>), and -fiber <100>||RD ({001}<100>-{011}<100>). The calculated lattice correspondence between parent phase and martensite using the notation of the correspondence variant from Miyazaki, where {110}<110> parent phase variant corresponds to {111}<211> and {002}<002> martensite variants; and {111}<110> parent phase corresponds to {210}<211> and {210}<002> [8].…”