Effect of Texture on the Grain-Size-Dependent Functional Properties of NiTi Shape Memory Alloys and Texture Gradient Design: A Phase Field Study

Abstract

Texture is inevitably introduced during the manufacturing of most NiTi shape memory alloys (SMAs), and the textured nanocrystalline NiTi has been extensively employed in engineering. However, the effect of texture, and the joint effect of grain size (GS) and texture on the functional properties of NiTi SMAs and the corresponding microscopic mechanisms have not been clearly understood yet. In this work, based on the phase field method, the effect of texture on the GS-dependent functional properties of NiTi SMAs, including super-elasticity (SE), one-way shape memory effect (OWSME), and stress-assisted two-way shape memory effect (SATWSME), is investigated, and the corresponding microscopic mechanisms are revealed. Moreover, the samples with discrete geometrical gradients and/or texture gradients are designed to achieve graded functional properties. The simulation results indicate that the dependence of functional properties on texture is due to the effect of crystallographic orientation on martensite transformation and reorientation, which can lead to different inelastic strains. In the designed samples with texture gradients, the stress–strain responses of sheets with various textures are different, allowing for the coordination of overall deformation of the sample by combining such sheets, with varying inelastic deformation degrees. Thus, the overall response of the sample differs from that without texture gradient, leading to the achievement of graded functional properties. The simulation results and new findings in this work contribute to a deeper understanding of the effects of texture, GS, and their interaction on the functional properties of SMAs, and provide valuable reference for the design and development of SMA-based devices with desired functional properties.