Complex Actuation Response of Functionally Graded High Temperature Shape Memory Alloys

Abstract Shape Memory Alloys (SMAs) are multifunctional materials with various properties useful for aerospace applications. Developments of Additive Manufacturing (AM) approaches for SMAs has allowed for greater customization in regards to the geometry of components. In addition to complex shapes, Functionally Graded (FG) SMAs are another possibility enabled by AM. In this work, FG NiTiHf produced via laser powder bed fusion is studied. The functional grading is achieved through tuning of the laser scanning parameters to selectively alter the alloy composition and thus the phase transformation properties. Thermome-chanical modeling is performed to better understand the behavior of the FG NiTiHf and inform aspects of its design. The NiTiHf properties are extremely sensitive to processing history, which can be highly inconsistent due to the large number of impactful factors in AM approaches. Thus, approximation techniques to account for material property variability in the constitutive models are explored. Furthermore, by the very nature of an FG sample, there may be too many compositions to feasibly characterize each individually. To address these points, an SMA constitutive model is first established for calibration of characterized samples. A generalized parameters calibration approach is then proposed to predict the thermomechanical response of compositionally similar alloys. The generalized parameters are informed by differential scanning calorimetry in an effort to minimize the experimental burden of full thermomechanical characterization. The predictive capabilities of the approach are assessed. Beyond use as a prediction tool for FG SMAs, the modeling presented in this work can be used for inverse design to determine requirements of constituent alloys for achieving desired behaviors.