Ti-22Al-25Nb (at.%)合金O相层片高温变形动态球化行为

Dynamic globularization behavior of O-phase lamellae in Ti-22Al-25Nb (at.%) alloy during deformation at elevated temperatures

摘要:

为阐明 Ti2AlNb基合金高温变形过程中O相层片的球化机制及模型,研究了Ti-22Al-25Nb(at.%)合金在(O+B2)和(α2+O+B2)相区压缩变形行为及显微组织演变规律。结果表明,合金的软化行为与O相层片动态球化、45°方向剪切变形失稳及裂纹萌生有关。O相层片在较低温度和较高应变速率下难以球化是由于原子具有较低的扩散速率和较短的扩散时间。O相层片的球化机制主要为层片扭结和剪断,本质上属于动态再结晶行为。建立了合金高温变形本构关系,并计算了变形激活能为831 kJ?mol^(-1) ；对O相层片球化的动力学过程进行了研究,其动力学行为受变形条件影响很大,遵循阿夫拉米曲线方程。

Abstract:

To clarify the globularization mechanism and model of the O-phase lamellae of Ti2AlNb-based alloys during deformation at elevated temperatures, the hot deformation behavior and microstructure evolution of Ti-22Al-25Nb (at.%) alloy during hot compression deformation in (α2+O+B2) region were investigated. The results showed that the flow softening is relevant to the dynamic globularization of O-phase lamellae and the flow instability including 45° shear deformation, 45° shear cracking and micro-cracks. The deformation constitutive model based on the exponential law was established and the deformation activation energy was calculated to be 831 kJ?mol-1. The globularization of O-phase lamellae is hard to occur at low temperatures or at high strain rates due to slow diffusion rate or insufficient diffusion time. The main globularization mechanism is the kink and shear of the O-phase lamellae, which is confirmed to be a dynamic recrystallization behavior. The dynamic globularization kinetics was also studied, which is sensitive to deformation conditions including deformation temperatures and strain rates and follows an Avrami type sigmoid equation.