Precipitation of Ni₄Ti₃ is effective in tuning martensitic transformations (MTs) in NiTi shape memory alloys (SMAs). However, several fundamental issues concerning the influence of Ni₄Ti₃ on MTs remain unclear. In this study, the microstructure evolution process during precipitation and its influence on B2→R MT are investigated using computer simulations based on the phase field method. In particular, the roles played by Ni concentration gradient in the B2 matrix and internal coherency stress fields associated with different precipitate microstructures are analyzed in detail. It is found that Ni concentration gradient in the B2 matrix created by Ni₄Ti₃ precipitates alters significantly local martensitic start temperature and the overall MT behavior, while the internal coherency stress field associated with the Ni₄Ti₃ precipitates dictates the structure of martensitic domains via variant selection. The latter effect makes it promising to develop Invar alloys via stress-ageing to tailor the precipitate microstructure. These findings provide fundamental insights into the mechanism controlling the MT behavior in precipitate-bearing SMAs and provide guidance for the design of thermomechanical treatment for desired precipitate microstructures and the corresponding MT behavior.

Ni ₄ Ti _3的沉淀可有效调节NiTi形状记忆合金（SMAs）中的马氏体相变（MTs）。然而，关于Ni ₄ Ti ₃对MT的影响的几个基本问​​题仍然不清楚。本研究利用基于相场法的计算机模拟研究了降水过程中的微观结构演变过程及其对B2→R MT的影响。特别是，详细分析了B2基质中Ni浓度梯度和与不同析出物微观结构相关的内部相干应力场的作用。发现Ni ₄ Ti ₃在B2基体中产生Ni浓度梯度Ni ₄ Ti ₃析出物的内部相干应力场通过变体选择决定了马氏体畴的结构，从而显着改变了局部马氏体起始温度和整体MT行为。后一种效应使其有望通过应力时效来开发Invar合金以调整析出物的微观结构。这些发现为控制含沉淀物SMA中MT行为的机理提供了基本的见识，并为所需的沉淀物微结构和相应的MT行为的热机械处理设计提供了指导。