Porous NiTi shape memory alloys (SMA) have been developed into important biomedical and damping materials. However, the effect of pore on the martensitic microstructure evolution, functional properties, and plastic deformation has not been fully clear yet. In this work, to reveal the functional properties including superelasticity (SE), elastocaloric effect (eCE), one-way shape memory effect (OWSME), and stress-assisted two-way shape memory effect (SATWSME), as well as plastic deformation of porous NiTi SMAs, the polycrystalline SMA system is considered as a composite containing the grain-interior (GI) and grain-boundary (GB) phases, a thermo-mechanically coupled, grain-size-dependent and crystal-plasticity-based phase field model is proposed for the GI phase, and an elasto-viscoplastic constitutive model is established for the GB phase. The effects of porosity, pore diameter, pore aspect ratio, pore orientation, and pore distribution, as well as the interaction between pore and grain size, are comprehensively revealed and discussed. The simulations demonstrate that the pores cause a heterogeneous stress field, and the interaction among pores and that between pores and grain boundaries can enhance such heterogeneity, which can promote the initiation of martensitic transformation and reorientation. Moreover, the geometrical constraints caused by the pores can significantly affect the morphology and evolution of martensite microstructures. However, due to the diverse microstructure evolutions during SE, OWSME, and SATWSME, their interactions with the pores are quite different, resulting in various dependencies of each functional property and plastic deformation on the pore, and such dependencies are strongly influenced by porosity, pore diameter, pore aspect ratio, pore orientation, and pore distribution. The simulated results in this work are helpful to comprehensively and deeply understand the pore effect and its microscopic mechanism.

中文翻译：

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孔隙对 NiTi 形状记忆合金变形行为的影响：基于晶体塑性的相场建模

多孔镍钛形状记忆合金（SMA）已发展成为重要的生物医学和阻尼材料。然而，孔隙对马氏体微观结构演变、功能性能和塑性变形的影响尚未完全清楚。在这项工作中，揭示了包括超弹性（SE）、弹热效应（eCE）、单向形状记忆效应（OWSME）和应力辅助双向形状记忆效应（SATWSME）以及塑性变形在内的功能特性对于多孔 NiTi SMA，多晶 SMA 系统被认为是包含晶粒内部 (GI) 和晶界 (GB) 相的复合材料，这是一种热机械耦合、晶粒尺寸相关且基于晶体塑性的相场提出了GI相的模型，并建立了GB相的弹粘塑性本构模型。全面揭示和讨论了孔隙率、孔径、孔隙纵横比、孔隙取向和孔隙分布的影响，以及孔隙与晶粒尺寸之间的相互作用。模拟结果表明，孔隙引起不均匀应力场，孔隙之间以及孔隙与晶界之间的相互作用可以增强这种不均匀性，从而促进马氏体相变和再取向的引发。此外，由孔隙引起的几何约束可以显着影响马氏体微观结构的形态和演化。然而，由于SE、OWSME和SATWSME期间的微观结构演化不同，它们与孔隙的相互作用有很大不同，导致每种功能性质和塑性变形对孔隙的依赖性不同，并且这种依赖性受到孔隙率、孔隙率的强烈影响。直径、孔纵横比、孔方向和孔分布。本工作的模拟结果有助于全面、深入地理解孔隙效应及其微观机制。