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论文题目： Deformation mechanism of fine structure and its quantitative relationship with quasi-static mechanical properties in near β-typeTi-4.5Mo-5.1Al-1.8Zr-1.1Sn-2.5Cr-2.9Zn alloy

发表时间：Available online 14 September 2021

发表期刊： Progress in Natural Science: Materials International [ 点击下载PDF ]

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Fig. 6 shows the microstructures of the β_T regions in the completely heat-treated specimens. In 880 °C AC specimen, the thickness of acicular α_s was about 0.13 μm, and the inter-particle spacing of α_s was about 0.11 μm, as shown in Fig. 6(a). However, the thickness values of αs in the 920 °C AC specimen and the 920 °C WQ specimen were 0.081 μm and 0.056 μm, respectively, and the corresponding inter-particle spacing values of α_s were 0.072 μm and 0.049 μm, as shown in Fig. 6(b) and (c).

Fig. 6. Magnified microstructures of the completely heat-treated specimens. (a) 880 °C AC specimen, (b)920 °C AC specimen and (c) 920 °C WQ specimen.

The microstructure observation was carried out on the regions near and far from the fracture line of the failure specimen, and the TEM images are shown in Fig. 9.Fig. 9(a) shows the TEM morphology of the region far from the fracture line. Fig. 9(a1) is the high magnification view showing the microstructure of the intersection of α_p and β matrix, and Fig. 9(a2) and Fig. 9(a3) are the selected area diffraction patterns (SADP) of circles a2 and a3 in Fig. 9(a), respectively. In the slight deformation region shown in Fig. 9(a) and (a1), the accumulated dislocations at the intersection of α_p and β matrix were observed, while in the β matrix separated by acicular α_s, only a small amount or no dislocations nucleated. This indicates that softer α_p deformed firstly at the initial stage of deformation, which is consistent with the report by Zhu et al. [23]. Fig. 9(b) shows the TEM morphology of the region near the fracture line, in which Fig. 9(b1) is the high magnification view showing the microstructure of the intersection of α_p and β matrix, and Fig. 9(b2) and Fig. 9(b3) are SADP of circles b2 and b3 in Fig. 9(b), respectively. In the severe deformation region shown in Fig. 9(b) and (b1), a large number of dislocations were accumulated in α_p and β matrix. This indicates that with the increase of deformation, α_p further deformed and the deformation of the β matrix separated by α_s was also activated. However, no dislocation was observed in acicular α_s, which indicates that the harder acicular α_s was not involved in the deformation.

Fig. 9. TEM images of the failure specimen. (a) Far from the fracture line and (b) near the fracture line.

The schematic illustration of the deformation process of the fine structure containing lamellar α_p and acicular α_s is shown in Fig. 10. At the initial stage of deformation shown in Fig. 10(a), the plastic deformation mainly occurred in softer α_p. With the increase of deformation, the hardened layers composed of accumulated dislocations formed at α_p boundaries, which is similar to the composite-like materials consisting of interiors with low flow stress and hardened layers of grain boundaries [32,33]. At this time, the hardened α_p activated the deformation of β matrix, as shown in Fig. 10(b). During the subsequent deformation, the hardened α_p and β matrix separated by acicular α_s continued to deform, as shown in Fig. 10(c).

Fig. 10. Schematic illustration of the deformation process of the fine structure. (a) The microstructure at the initial stage of deformation, (b) the hardened α_p activating the deformation of β matrix and (c) the compatible plastic deformation in high strain.