Wang Zifan, Chen Jingwei, Kocich Radim, Tardif Samuel, Dolbnya Igor P, Kunčická Lenka, Micha Jean-Sébastien, Liogas Konstantinos, Magdysyuk Oxana V, Szurman Ivo, Korsunsky Alexander M
MBLEM, Department of Engineering Science, University of Oxford, Oxford OX1 3PJ, U.K.
Faculty of Mechanical Engineering, Brno University of Technology, Technická 2896/2, Brno 61669, Czech Republic.
ACS Appl Mater Interfaces. 2022 Jul 13;14(27):31396-31410. doi: 10.1021/acsami.2c05939. Epub 2022 Jun 27.
To explore an effective route of customizing the superelasticity (SE) of NiTi shape memory alloys via modifying the grain structure, binary NiTi (wt) alloys were fabricated in as-cast, hot swaged, and hot-rolled conditions, presenting contrasting grain sizes and grain boundary types. synchrotron X-ray Laue microdiffraction and synchrotron X-ray powder diffraction techniques were employed to unravel the underlying grain structure mechanisms that cause the diversity of SE performance among the three materials. The evolution of lattice rotation, strain field, and phase transformation has been revealed at the micro- and mesoscale, and the effect of grain structure on SE performance has been quantified. It was found that (i) the NiTi and NiTi precipitates are similar among the three materials in terms of morphology, size, and orientation distribution; (ii) phase transformation happens preferentially near high-angle grain boundary (HAGB) yet randomly in low-angle grain boundary (LAGB) structures; (iii) the smaller the grain size, the higher the phase transformation nucleation kinetics, and the lower the propagation kinetics; (iv) stress concentration happens near HAGBs, while no obvious stress concentration can be observed in the LAGB grain structure during loading; (v) the statistical distribution of strain in the three materials becomes asymmetric during loading; (vi) three grain lattice rotation modes are identified and termed for the first time, namely, multi-extension rotation, rigid rotation, and nondispersive rotation; and (vii) the texture evolution of B2 austenite and B19' martensite is not strongly dependent on the grain structure.
为了探索通过改变晶粒结构来定制镍钛形状记忆合金超弹性（SE）的有效途径，制备了铸态、热锻造和热轧条件下的二元NiTi（重量）合金，呈现出不同的晶粒尺寸和晶界类型。采用同步辐射X射线劳厄微衍射和同步辐射X射线粉末衍射技术，揭示了导致这三种材料SE性能差异的潜在晶粒结构机制。在微观和中观尺度上揭示了晶格旋转、应变场和相变的演变，并对晶粒结构对SE性能的影响进行了量化。结果发现：（i）三种材料中的NiTi和NiTi析出物在形态、尺寸和取向分布方面相似；（ii）相变优先发生在高角度晶界（HAGB）附近，而在低角度晶界（LAGB）结构中随机发生；（iii）晶粒尺寸越小，相变形核动力学越高，传播动力学越低；（iv）应力集中发生在HAGB附近，而在加载过程中LAGB晶粒结构中未观察到明显的应力集中；（v）三种材料在加载过程中应变的统计分布变得不对称；（vi）首次识别并命名了三种晶粒晶格旋转模式，即多扩展旋转、刚性旋转和非分散旋转；（vii）B2奥氏体和B19'马氏体的织构演变与晶粒结构没有强烈的依赖关系。
