Ti-55钛合金板材的超塑性变形及组织演变

Superplastic Deformation and Microstructure Evolution of Ti-55 Alloy Sheet

研究了Ti-55钛合金板材在应变速率为8.30×10^(-4)～1.32×10^(-2)s^(-1)、变形温度885～935℃条件下的超塑性拉伸变形行为和显微组织演化。结果表明:细晶Ti-55钛合金板材表现出良好的超塑性,在温度925℃和应变速率为6.64×10^(-3)s^(-1)条件下,最大延伸率可达987%,即使在1.32×10^(-2)s^(-1)的高应变速率条件下也获得了872%的断裂延伸率。在应变速率不变的条件下,变形温度的升高,动态再结晶程度增大,有利于细小等轴的α相晶粒发生相转变。变形速率的不断降低,α相晶粒容易聚集并长大,α相含量减少,β相含量增加,材料塑性反而有所下降。此外,在超塑性变形的过程中,变形区域晶粒长大速度要大于夹头区域,随着变形程度的增大,α相的含量也随之减少,Ti-55材料的变形能够促使晶粒的聚合长大和α相的相转变。

The superplastic deformation and microstlucture evolution at different temperatures （885 -935 ℃ ） and strain rates （8.30 ×10-4 - 1.32 × 10-2 s-1 ） were investigated. The results showed that the fine-grained Ti-55 alloy sheet exhibited good super- plastic deformation performance. The maximum elongation of 987% could be achieved at 925 ℃ and 6.64× 10 -3 s i , and the high e- longation of 872% could be obtained at a high strain rate of 1.32 × 10 2 s-1. At the same strain rate, with the increasing deformation temperature, the extent of dynamic recrystallization increased and the volume fraction of α phase decreased, which promoted α phase transformation. Meanwhile, the primary α phase grains could be refined. At the same superplastic tension temperature, the primary phase grains could coarsen and the content of β phase increased with the strain rate decreasing. Additionally, the coarsening degree of α phase grains in the deformed gauge became more serious than that in the undeformed grip. The content of α phase decreased with the increase of deformation degree. The deformation of Ti-55 alloy material could accelerate the coarsening rate of α phase grains and promote α to β phase transformation.