包覆轧制TC4细晶板材组织性能演化规律

Effect of Clad Rolling Process on Microstructure and Properties Evolution of Fine-Grain TC4 Alloy Sheet

摘要:

研究了初始组织为α′马氏体的TC4合金板材在两相区降温包覆轧制及热处理过程中的组织/织构演化规律，分析了晶粒尺寸、位错密度及织构对合金强度及强度各向异性的影响。结果表明：合金β淬火后可获得多尺度、多变体细针状α′马氏体组织。两相区包覆轧制可显著细化晶粒，形成平均尺寸约0.89 μm的超细晶组织与＜ 0001 ＞//ND的B型织构。然而轧态组织呈现细小等轴再结晶晶粒与尺寸较大的变形晶粒组成的混晶组织。板材退火过程中发生静态再结晶（SRX），组织均匀性提高。同时，退火处理不改变板材的织构类型，且Basal型织构强度略有增强。强Basal型织构使得合金的柱面＜a＞滑移的施密特因子在TD和RD 2个方向趋于接近，导致横纵向力学性能差异降低。随着退火温度的升高，板材强度降低，其源于晶粒尺寸增加与位错密度降低的协同作用。研究表明，利用两相区包覆轧制/退火工艺可成功制备出横纵向强度差异小的细晶TC4合金板材，板材平均晶粒尺寸约2 μm。为航空航天高性能钛合金制备提供理论基础与技术支撑。

Abstract:

The microstructure evolution of TC4 alloy plates with α martensitic as primary microstructure in dual-phase region during clad rolling and annealing were investigated. The relationship between microstructure evolution (grain size, texture) and strength of the alloy was discussed. The results show that β-quenched alloy exhibits fine lamellae α′ martensite which displays multi-scale and multi-variant distribution. The grain of β-quenched alloy is significantly refined with average grain size of 0.89 μm and <0001>//ND of Basal texture forms after two-phase cross rolling. However, a mixed structure, consisting of fine recrystallized grains and coarse deformed grains, is observed. During annealing process, the rolled samples undergo continuous static recrystallization, resulting in the formation of fine equiaxed grain (approximately 1.86 μm at 720 ℃). Meanwhile, annealing treatment do not change the texture type, while the intensity of Basal texture is slightly enhanced. The strong Basal texture makes the Schmidt factor of prismatic <a> slip close to each other along the direction of TD and RD, which results in the decrease in strength difference between transverse and longitudinal direction. The strength of the sheet decreases with the increase in annealing temperature, which is due to the synergistic effect of the increase in grain size and the decrease in dislocation density. The result shows that the fine grained TC4 alloy with Basal texture can be fabricated by using α+β phase cross rolling and annealing, which provides a theoretical basis and technical support for the preparation of fine-grain titanium alloy plates for aerospace applications.