Deformation mechanism of fine structure and its quantitative relationship with quasi-static mechanical properties in near β-type Ti-4.5Mo-5.1Al-1.8Zr-1.1Sn-2.5Cr −2.9Zn alloy

The deformation mechanism of the fine structure composed of primary α phase (α_p) and acicular secondary α phase (α_s) on quasi-static mechanical properties is still not very clear. The main controversy is focused on the role of α_p in the mechanical behavior. In this paper, the microstructure of the heat-treated near β-type Ti-4.5Mo-5.1Al-1.8Zr-1.1Sn-2.5Cr-2.9Zn alloy after tensile tests was observed by transmission electron microscopy (TEM). And the results showed that in the slight deformation region the dislocations were accumulated at the intersection of α_p and β matrix separated by α_s, while only a few dislocations nucleated in β matrix. In the severe deformation region, a large quantity of dislocations in both α_p and β matrix were observed. It can be inferred that α_p deformed firstly and then activated the deformation of β matrix, that is, the thickness of α_p and the inter-particle spacing of α_s played a dominant role in the deformation process. The quantitative relationship between the yield strength and the microstructure parameters is consistent with this inference. By adjusting the solution treatment parameters and the subsequent aging treatment, three fine structures were obtained, and the corresponding mechanical properties were determined. Furthermore, the yield strength can be described by the mathematical model σ_y ​= ​756.4 ​+ ​135.6/h_p^1/2 +32.2/d_s^1/2, where h_p and d_s are the thickness of α_p and the inter-particle spacing of α_s, respectively.