Ti-5A1-5Mo-5V-3Cr-1Zr近β钛合金在不同α/β界面取向条件下的针状α亚结构形成与破碎行为

Sub-structure Formation and Fragmentation of Acicular α Phase at the Different Orientation of α/β interface in Ti-5A1-5Mo-5V-3Cr-1Zr near β Titanium Alloy

摘要:

对初始针状α组织的Ti-5A1-5Mo-5V-3Cr-1Zr近β钛合金在750~775 ℃、10_-3~10_-1 s_-1下热压缩,研究针状α的微观破碎行为。结果表明,随着应变量的增加,针状α经历了旋转位移、部分破碎、完全破碎成等轴形貌的演变阶段。在针状α破碎过程中,当相邻α和β之间符合Burgers取向关系时,β基体内位错通过α/β界面滑移传递切入α内,形成高密度位错,并演化成亚晶结构。当不符合Burgers取向关系时,β基体位错容易在一些取向差异较大的α/β界面塞积、出现局部应力集中,导致在对应针状α内形成局部剪切带相关的亚结构。随后,β基体沿亚结构界面契入针状α内,最终导致针状α相分离破碎。提升温度会加剧β基体动态回复,位错密度大幅下降,不利于在针状α内形成亚结构；提升变形速率使得变形时间大幅缩短,针状α内形成高密度位错、进而转变成亚结构等微观过程无法充分进行,因此均会降低针状α的破碎程度。

Abstract:

Ti-5A1-5Mo-5V-3Cr-1Zr near β titanium alloy containing the initial acicular α was hot compressed at 750~775 ℃ and 10-3~10_-1 s_-1, in which the fragmentation behavior of acicular α was investigated. With the increasing of strain, the acicular α undergoes the rotation displacement, partial fragmentation up to transform to the equiaxial morphology completely. During the fragmentation of acicular α, when the Burgers orientation relationship exists between neighbor α and β phases, the dislocations in β matrix are easy to enter into the neighbor acicular α through slip transmission at α/β interface, followed by the formation of high-density dislocations and then transforming to the sub-microstructures in acicular α. In case of no Burgers orientation relationship between neighbor α and β phases, the dislocations pile up at some α/β interface with the large orientation discrepancy. The as-resulted local stress concentration causes the formation of sub-microstructures composing of local shear bands in acicular α. Sequentially, β matrix hedges into the acicular α along the interfaces among sub-microstructures, leading to the fragmentation of acicular α. The increasing of temperature promotes the dynamic β recovery and then decreases the dislocation density, which doesn’t benefit the formation of sub-microstructures in acicular α. The increasing of strain rate decreases the deformation time, which suggests that the formation of high-density dislocations and then transformation to the sub-microstructures may not perform sufficiently in acicular α. As a result, the increasing of temperature and strain rate both delay the fragmentation of acicular α.