Deformation Defects Characterization in Short-range Ordered CrCoNi using Fast Electron Detectors and 4D-STEM
Deformation Defects Characterization in Short-range Ordered CrCoNi using Fast Electron Detectors and 4D-STEM
复制标题
使用快速电子探测器和 4D-STEM 表征短程有序 CrCoNi 的变形缺陷
DOI：
10.1093/micmic/ozad067.113
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发表时间：
2023
影响因子：
2.8
通讯作者：
Zuo, Jian-Min
中科院分区：
文献类型：
--
作者：
Yin, Kaijun;Hsiao, Haw-Wen;Feng, Rui;Liaw, Peter K;Zuo, Jian-Min
CrCoNi是一种具有单相面心立方（FCC）结构的中熵合金（MEA），由于其具有高强度和高延展性[1]以及短程有序（SRO）效应等优点，受到了研究者的广泛研究[2,3]。CrCoNi优异的力学性能归因于新的变形机制，如层错（SFs）、纳米孪晶（NTs）、剪切带等的形成[4,5]。晶体缺陷一般是用电子显微镜成像的。然而，晶体变形的短程序效应还没有完全被理解。变形缺陷的表征传统上是使用透射电镜内部的衍射对比成像进行的。最近，弱光束暗场扫描透射电子显微镜（WB-DF STEM）被用于表征CrCoNi中的解离位错，并确定两个平行SFs之间的距离[7,8]。WB-DF STEM允许直接区分肖克利部分位错，从而测量两个部分之间的堆积断层宽度。然而，WB-DF成像和这些sf的识别和计数都是耗时的过程，这是变形分析的主要瓶颈。另一个挑战是，这种分析通常局限于孤立的位错和严重变形的区域，很难分析。本文介绍了一种基于电子漫射散射倒谱分析的缺陷成像方法。这种直接电子探测器具有高动态范围和快速读数，为高空间分辨率表征[9]提供了大的衍射数据集。通过比较区域差倒谱（dCp）[10]与STEM实时空间图像，对变形CrCoNi样品中SFs和NTs的局部晶体缺陷进行了成像和分析。到目前为止，我们已经成功地获得了一个大的晶格缺陷数据集及其相应的衍射和倒谱图。直接电子图像和倒谱模式之间的相关性使单个SF和nt之间的分离成为可能。通过总结不同CrCoNi样品在外加热退火前后层错宽度的局部变化，可以看出层错能（SFE）的分布，以及SRO的影响。原子分辨率STEM成像进一步证明了SRO的存在。这些鼓舞人心的结果为自动表征SRO的存在和类别以及它们与位错的相互作用，导致平面缺陷的形成提供了可能性。本报告将总结目前为止我们在CrCoNi b[11]的新型变形机制方面的研究进展。
CrCoNi, a Medium-Entropy Alloy (MEA) with a single-phase face-centered-cubic (FCC) structure, has been extensively studied by researchers since it has shown great advantages of high strength and great ductility [1], as well as the short-range ordering (SRO) effects [2, 3]. The exceptional mechanical properties of CrCoNi have been attributed to novel deformation mechanisms such as the formation of stacking faults (SFs), nanotwins (NTs), shear bands, etc [4, 5]. Crystalline defects in general are imaged by electron microscopy. However, short-range order effects on crystal deformation have not been fully understood. Characterization of deformation defects is traditionally carried out using diffraction contrast imaging performed inside a TEM [6]. More recently, weak-beam dark-field scanning transmission electron microscopy (WB-DF STEM) has been used to characterize the dissociated dislocations in CrCoNi and identify the distance between two parallel SFs [7, 8]. WB-DF STEM allows Shockley partial dislocations to be directly distinguished and thus a measurement of the stacking fault width between the two partials. However, both WB-DF imaging and the identification and counting of these SFs are time consuming processes, which is a major bottleneck for deformation analysis. The other challenge is that such analysis in generally limited to isolated dislocations and regions heavily deformed are difficult to analyze.Here, we introduce a novel defect imaging method based on the cepstral analysis of electron diffuse scattering using an Electron Microscope Pixel Array Detector (EMPAD) detector. This direct electron detector has a high dynamic range and fast readout, providing large diffraction datasets for high spatial resolution characterization [9]. By comparing regional difference cepstrums (dCp)[10] with real-space images from STEM, the local crystal defects of SFs and NTs are imaged and analyzed in deformed CrCoNi samples. By far, we have successfully obtained a large dataset of lattice defects and their corresponding diffraction and cepstral patterns. Correlation between direct electron images and cepstral patterns enable a separation between single SF and NTs. By summarizing the local variations of stacking fault width in different CrCoNi samples before and after additional thermal annealing, we could show the distribution of stacking fault energy (SFE), and the impact of SRO. The presence of SRO is further evidenced by atomic resolution STEM imaging. These inspiring results open the possibility of the auto characterization of the presence and the category of SRO and their interactions with dislocations, leading to the formation of planar defects. This talk will summarize our progress so far on the novel deformation mechanisms in CrCoNi [11].