Plummer Gabriel, Mendelev Mikhail I, Benafan Othmane, Lawson John W
KBR Inc., Intelligent Systems Division, NASA Ames Research Center, Moffett Field, CA 94035, United States of America.
Intelligent Systems Division, NASA Ames Research Center, Moffett Field, CA 94035, United States of America.
J Phys Condens Matter. 2023 Sep 13;35(49). doi: 10.1088/1361-648X/acf6a3.
Martensitic transformations in shape memory alloys are often accompanied by thermal hysteresis, and engineering this property is of prime scientific interest. The martensitic transformation can be characterized as thermoelastic, where the extent of the transformation is determined by a balance between thermodynamic driving force and stored elastic energy. Here we used molecular dynamics simulations of the NiTi alloy to explore hysteresis-inducing mechanisms and thermoelastic behavior by progressively increasing microstructural constraints from single crystals to bi-crystals to polycrystals. In defect-free single crystals, the austenite-martensite interface moves unimpeded with a high velocity. In bi-crystals, grain boundaries act as significant obstacles to the transformation and produce hysteresis by requiring additional nucleation events. In polycrystals, the transformation is further limited by the thermoelastic balance. The stored elastic energy can be converted to mechanisms of non-elastic strain accommodation, which also produce hysteresis. We further demonstrated that the thermoelastic behavior can be controlled by adjusting microstructural constraints.
形状记忆合金中的马氏体相变通常伴随着热滞现象，研究并操控这一特性具有重要的科学意义。马氏体相变具有热弹性特征，其转变程度由热力学驱动力与储存的弹性能之间的平衡决定。在此，我们通过对镍钛合金进行分子动力学模拟，逐步增加微观结构约束条件（从单晶到双晶再到多晶），来探究热滞诱导机制和热弹性行为。在无缺陷的单晶中，奥氏体 - 马氏体界面高速无阻地移动。在双晶中，晶界成为相变的重大障碍，通过要求额外的形核事件产生热滞。在多晶中，相变进一步受到热弹性平衡的限制。储存的弹性能可转化为非弹性应变调节机制，这也会产生热滞。我们还进一步证明，热弹性行为可通过调整微观结构约束来控制。
