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.

由初生α相(α _p )和针状次生α相(α _s )组成的精细结构对准静态力学性能的变形机制尚不十分清楚。主要争议集中在 α _p在机械行为中的作用。本文采用透射电子显微镜(TEM)观察了热处理后的近β型Ti-4.5Mo-5.1Al-1.8Zr-1.1Sn-2.5Cr-2.9Zn合金在拉伸试验后的显微组织。结果表明，在轻微变形区域，位错聚集在α _p和β 基体相交处，相隔α _s, 而只有少数位错在 β 矩阵中成核。在严重变形区，在α _p和β 基体中均观察到大量位错。可以推断，α _p先变形，然后激活了β基体的变形，即α _p的厚度和α _s的颗粒间距在变形过程中起主导作用。屈服强度与显微组织参数之间的定量关系与这一推论是一致的。通过调整固溶处理参数和随后的时效处理，获得了三种精细组织，并确定了相应的力学性能。此外，屈服强度可以用数学模型σ _y  = 756.4 + 135.6/ h _p ^1/2 + 32.2/ d _s ^{1/2 来描述}，其中h _p和d _s是 α _p和α _s的粒子间距， 分别。