厚板热轧开坯Ti-44Al-5Nb-1Mo-(V, B)合金的显微组织及热变形能力

Effects of Primary Hot-Rolling Process on the Microstructure and Deformability of Ti-44Al-5Nb-1Mo-2V-0.2B Alloys

摘要:

采用Marc有限元模拟软件对Ti-44Al-5Nb-1Mo-2V-0.2B合金的厚板热轧开坯过程进行模拟,建立了三维热力耦合有限元模型,分析了轧制过程中TiAl合金不同位置的温度、等效应力和等效应变等,重点关注了沿厚板厚度方向的等效塑性应变分布特征。基于模拟结果,对Ti-44Al-5Nb-1Mo-2V-0.2B合金进行了厚板热轧开坯,考察了板材沿厚度方向的显微组织演变规律及开坯工艺对其热变形能力的影响。结果表明,开坯板材的显微组织主要由少量的残余片层和细小的B2、γ和α2多相混合组织组成,由板材边缘至心部的等效塑性应变逐渐升高,这使组织中残余片层的含量由板材边缘至心部逐渐降低,板材心部的组织会发生较大程度的流变软化。基于厚板热轧开坯工艺对显微组织的影响规律,初步确定了Ti-44Al-5Nb-1Mo-2V-0.2B合金的薄板制备工艺。在该合金的板材制备工序中,随着板材厚度的降低,应适当增加回炉次数或延长回炉时间,并减小轧制变形量,以降低板材心部至边缘的温度和应变分布梯度,同时,在轧制工序后期,可通过提高轧制温度实现显微组织进一步细化。

Abstract:

In this work, the hot rolling process of Ti-44Al-5Nb-1Mo-2V-0.2B thick plates was simulated using the Marc finite element simulation software. A three-dimensional thermomechanical coupled finite element model was established to analyze the temperature, equivalent stress, and equivalent strain at various positions of the TiAl alloy during rolling, with a particular focus on the distribution characteristics of equivalent plastic strain along the thickness direction of the thick plates. Subsequently, the hot-pack rolling of the Ti-44Al-5Nb-1Mo-2V-0.2B alloy was performed based on the simulation results. The investigation encompassed the evolution of the microstructure along the thickness direction of the TiAl alloy and the impact of the primary rolling on its thermal deformation capacity. The obtained results reveal that the microstructure of the primary rolled sheets predominantly comprises a small amount of residual laminae and fine mixed phases consisting of B2, γ, and α2. The equivalent plastic strain increases gradually from the edge to the center of the sheets, leading to the significant softening of the microstructure in the center of the sheets. This effect induces a corresponding decrease in the residual laminae content from the edge to the center. Consequently, the preparation process for the Ti-44Al-5Nb-1Mo-2V-0.2B alloy was determined based on the influence of the hot rolling process on the microstructure. During the rolling process, as the sheet thickness decreases, it is advisable to appropriately increase the number of reheating cycles or extend the reheating time and simultaneously reduce the amount of rolling deformation. This approach helps minimize the temperature and strain distribution gradient from the core to the edge of the sheets. Additionally, in the later stages of the rolling process, further refinement of the microstructure can be achieved by raising the rolling temperature.