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论文题目： A new dynamic recrystallization mechanism in adiabatic shear band of an α/ β dual phase titanium alloy: Composition redistribution

发表时间：Available online 5 September 2021

刊源：Scripta Materialia 206 (2022) 114229 [ 点击下载PDF ]

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The microstructure and three-dimensional composition distri- bution of the transition region (the micro-deformation region between the ASB central region and the undeformed region, which reflects the parent microstructure and the atom distributions at a certain degree) are shown in Fig. 1 . Fig. 1 (a) indicates the TEM microstructure of the tip specimen, which shows that inhomoge- neous dislocations are distributed in the tip specimen. In fact, due to the quite different element contents between α phase and β phase, most dislocations are distributed in the GB of α phase and β phase. The 5 at. % Mo isosurface of the tip is shown in Fig. 1 (b). It indicates that the tip exhibits obvious Mo segregation and is composed of Mo-poor regions and Mo-rich regions with lamellar features. Moreover, the Mo-poor regions and Mo-rich regions distribute almost parallel to each other, separating the tip into six regions marked by symbols of G1-G6. Fig. 1 (c)-(h) exhibits the spatial distribution characteristics of Ti, Al, Cr, Zr, Mo and Sn. As shown in Fig. 1 (e) and (g), the poor regions of Mo and Cr are clearly distinguished by the arrows. However, significant difference of spatial distribution of Zr and Sn is not observed from Fig. 1 (f) and (h).

Fig. 1. The microstructure and composition distribution of the transition region. (a) TEM microstructure, (b) 5 at. % Mo isosurface, (c)-(h) three-dimensional composition distribution of alloying elements, and (i) one-dimensional concentration profile along the direction of blue column in (b).

The microstructure of the ASB central region is shown in Fig. 2 , in which Fig. 2 (a) and (b) are the dark field and bright field im- ages, respectively. It indicates that there are a lot of ultra-fine α and β grains in ASBs, as shown by the short white arrows. Accord- ing to the annular diffraction pattern in Fig. 2 (b), these ultra-fine grains are determined as DRX grains ( α_DRX and β_DRX ). Moreover, by comparing the characteristics of the bright regions in Fig. 2 (a) with that of the dark regions in Fig. 2 (b), it can be found that most of the dark regions in the viewing regions are due to the accumulated dislocations which distributed in the interface of DRX and deformed grains, as shown by the long white arrows. While in some local regions, the dark regions in Fig. 2 (b) may be induced by the diffraction contrast, as marked by the yellow dotted lines, because no corresponding bright regions are observed at the same locations in Fig. 2 (a).

Fig. 2. The microstructure in the ASB central region. (a) The dark field image, (b) the bright field image.

The microstructure and three-dimensional composition distribution of the ASB central region are shown in Fig. 3 . Fig. 3 (a) indicates the TEM microstructure of the tip specimen, in which most of the dark regions are due to the high density dislocations, while a small part of the dark regions are due to the diffraction contrast. By comparing the composition distribution of 5 at. % Mo isosurface with the TEM microstructure, the tip specimen can be separated into different sub-regions marked by symbols of G1-G7, as shown in Fig. 3 (b). Moreover, Mo segregation is also observed in ASBs, and the distribution characteristics of the accumulated dislocations are substantially consistent with that of the Mo segregation. Moreover, as shown in Fig. 3 (e) and (g), Mo and Cr show the similar segregation characteristics.

Fig. 3. The microstructure and composition distribution of the ASB central region. (a) TEM microstructure, (b) 5 at. % Mo isosurface, and (c)-(h) three-dimensional composition distribution of alloying elements.