铱单晶脆性与晶格动力学失稳相关性的多尺度模拟研究

Iridium (Ir) single crystal exhibits an anomalous brittle transgranular cleavage after a period of plastic deformation at ambient temperature. Most previous studies have focused on the effects of various dislocation mechanisms and impurity segregation at grain boundary on the brittleness of Ir, but there has not been a perfect theory to satisfactorily explain its brittleness, still waits for further study. Recent studies indicate that the anomalous brittleness of Ir may associate with its special lattice dynamics instability. This inspires us to explore the underlying mechanism of the brittle fracture of Ir in the viewpoint of lattice dynamics instability. For this purpose, the following three respects will be involved in this project: Firstly, a constitutive relationship and a Lattice Dynamics Finite-Element multiscale Method (LDFEM) will be constructed for modeling the deformation of Ir single crystal. On this basis, Multiscale modeling of uniaxial tension/compression, nanoindentation and micropillar compression of Ir single crystal will be performed by LDFEM; The simulation results will be combining with corresponding nanoindentation and micro-compression experiments, and comparatively analyze the mechanisms of lattice dynamics instability and microscopic deformation of Ir single crystal, to reveal the intrinsic relationship between the brittleness of Ir. The proposed studies will not only provide a new way for studying the brittleness of Ir, but also help drive the growth and application of multiscale material modeling.

铱单晶在室温下经过一定的塑性变形后发生脆性穿晶解理。关于铱脆性机理的前期研究多从晶界杂质和位错机制入手，至今依然没有形成统一的认识，还有待深入研究。近来研究表明，铱的反常脆性可能与其特殊的晶格动力学失稳有关。这启发我们从晶格动力学失稳的角度去探寻铱的脆性机理。为此，本项目拟开展三个方面的研究：首先构建铱单晶变形的力学本构关系和晶格动力学有限元(LDFEM)多尺度模拟方法；在此基础上开展铱单晶拉伸/压缩、纳米压痕和微柱压缩变形的多尺度模拟研究；开展纳米压痕和微柱压缩实验，结合多尺度模拟结果对比分析铱单晶的晶格动力学失稳与微观变形机理，揭示铱单晶脆性与晶格动力学失稳的关联性。项目研究不仅为探寻铱的反常脆性机理提供新的研究思路，也有利于多尺度材料模拟方法的发展和应用。

本项目针对铱单晶反常脆性及其晶格动力学稳定性开展了理论和实验研究。通过项目实施，构建了铱单晶的超弹性本构关系，发展了一种适用于稀贵及有色金属材料的多尺度串行材料模拟方法。采用该方法研究了铱单晶的弹塑性变形机制，探究铱单晶纳米压痕晶体结构失稳及初始塑性变形过程的位错形成及演化机制，并深入揭示铱单晶位错激活及结构演化的原因。开展铱单晶微柱压缩实验，揭示了铱单晶微柱压缩尺寸效应，阐明了铱单晶塑性变形以{111}<110>位错为主要滑移机制。拓展研究了Ir/Ir3Nb界面机制及杂质元素的影响规律，探讨了高温高压对Ir3Nb弹性、塑性、晶格动力学及热力学性质的影响。研究结果对理解Ir单晶反常脆性、弹塑性转变、Ir/Ir3Nb界面机制及Ir基合金脆性的相关研究有重要的理论参考价值。