Texture and grain neighborhood effects on Ni-Ti shape memory alloy performance

摘要

This work demonstrates how the statistical pseudoelastic performance of individual grains is affected by the local grain neighborhood in polycrystalline shape memory alloys (SMAs). This is achieved using a microstructural finite element (FE) model calibrated to homogenizedTi-50.9 at%Ni SMA. The results show a three-fold variation in the grain level axial transformation strain pT in randomly textured polycrystals, and a ～20-30% reduction in average p_T if plastically predeformed. A key outcome is a performance function to predict p_T of a grain, based on the orientations of the grain and its neighbors. Two key strategies to improve polycrystalline SMA performance areidentified. The first is to minimize the number of grain boundaries between high-and lowperforming grains: plate and bamboo geometries achieve this. The second is to employ high-symmetry orientation relationships between these grains. The results draw on recent experimental studies of grain level performance and provide a theoretical framework to interpret future diffraction tomography studies.