Determination of strain fields in porous shape memory alloys using micro-computed tomography

ABSTRACT Shape memory alloys (SMAs) belong to ‘intelligent’ material s since the metal alloy can change its macroscopic shape as the result of the temperature-induced, reversible martensite-austenite phase transition. SMAs are often applied for medical applications such as stents, hinge-less instruments, artificial muscles, and dental braces. Rapid prototyping techniques, including selective laser melting (SLM), allow fabricating complex porous SMA microstructures. In the present study, the macroscopic shape change s of the SMA test structures fabricated by SLM have been investigated by means of micro computed tomography (µCT ). For this purpose, the SM A structures are placed in to the heating stage of the µCT system SkyScan 1172™ (SkyScan, Kontich, Belgium) to acquire three-dimensional datasets above and below the transition temperature, i.e. at room temperature and at about 80 °C, respectivel y. The two datasets were registered on the basis of an affine registration algorithm with nine independent parameters – three for the translation, three for the rotation and three for the scaling in orthogonal directions. Essentially, the scaling parameters characterize the macroscopic deformation of the SMA structure of interest. Furthermore, applying the non-rigid registration algorithm, the three-dimensional strain field of the SMA structure on the micrometer scale co mes to light. The strain fields obtained will serve for the optimization of the SLM-process and, more important, of the design of the complex shaped SMA structures for tissue engineering and medical implants. Keywords: Shape memory alloy, selective laser melting, micro computed tomography, heating stage, registration, strain field