Cluster structure in amorphous Ti-Ni-Cu alloys subjected to high-pressure torsion deformation
Cluster structure in amorphous Ti-Ni-Cu alloys subjected to high-pressure torsion deformation
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DOI：
10.1016/j.jallcom.2018.03.357
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发表时间：
2018-06-15
影响因子：
6.2
通讯作者：
Valiev, R. Z.
中科院分区：
文献类型：
--
作者：
Gunderov, D. V.;Boltynjuk, E. V.;Valiev, R. Z.
用透射电子显微镜和扫描电子显微镜研究了Ti50Ni25Cu25非晶态Ti50Ni25Cu25合金在20℃和150℃高温高压扭转(HPT)后，在平面方向和横截面方向上的内部结构演变特征。在平面方向上，STEM HAADF观察到了亮度对比度为20 nm的区域。我们假设它们是“无定形纳米团簇”。在暗场电子显微镜图像中，许多区域显示了纳米晶(尺寸约为5 nm)，这是应变诱导纳米晶化的结果。在STEM HAADF图像中，可以看到由明亮的边界分隔的纳米团簇(尺寸约为20 nm)。在HPT处理后的片层横截面方向上发现了多组剪切带(SBS)。应变诱导纳米晶化直接在剪切带中形成纳米晶。在SBS周围的非晶相中也观察到了非晶态纳米团簇。在剪切带周围首次发现了非晶态纳米团簇的形成。用原子力显微镜(AFM)研究了离子抛光制备的薄膜的表面形貌。AFM显示了HPT处理状态下的空心状表面形貌，在透射电子显微镜图像中表现为纳米团簇对比度。这种空洞状的表面形貌可以用HPT处理状态下的刻蚀过程的特殊性来解释。通过拉伸试验测定了熔体快淬态Ti50Ni25Cu25在铸态和HPT处理后的脆性断裂。然而，与初始状态相比，受HPT的样品的断口表面的明显变化对应于局部延性的增加。(C)2018爱思唯尔B.V.保留所有权利。
The features of the internal structure's evolution of melt-spun (MS) amorphous Ti50Ni25Cu25 alloy samples subjected to high-pressure torsion (HPT) at 20 and 150 degrees C were revealed by TEM and STEM - in the planar direction and the cross-sectional direction of the HPT-processed disc-shaped samples.In STEM HAADF observations in the planar direction, areas with brightness contrast with a size of 20 nm are revealed. We assume them to be "amorphous nanoclusters". In dark-field TEM images, in many areas nanocrystals (with sizes about 5 nm) are revealed, resulting from strain-induced nanocrystallization. In STEM HAADF images, there can be seen nanoclusters (with sizes about 20 nm) separated by bright boundaries. Groups of shear bands (SBs) are revealed on the cross-sectional directions on lamellae cut from the HPT-processed samples. Nanocrystals form directly in the shear bands as a result of strain-induced nanocrystallization. Amorphous nanoclusters are also observed in the amorphous phase surrounding the SBs. Formation of the amorphous nanocluster in the areas surrounding the shear bands has been discovered for the first time. Atomic force microscopy (AFM) was used to study the surface morphology of foils prepared by ion polishing from the initial amorphous ribbons and HPT-processed samples. A hollows-like surface morphology in the HPT-processed state is revealed by AFM, which is reflected as nanocluster contrast in TEM images. The hollows-like surface morphology could be explained by the specifics of etching processes in the HPT-processed state. Brittle fracture of melt-spun Ti50Ni25Cu25 in the as-cast state and after HPT processing is determined during tensile tests. However, observable changes in the fracture surfaces correspond to an increased local ductility in samples subjected to HPT, in comparison with the initial state. (C) 2018 Elsevier B.V. All rights reserved.