冷轧TA5钛合金退火过程的再结晶行为及织构演变

采用电子背散射衍射技术(EBSD)对冷轧及退火态TA5钛合金板材的晶粒尺寸、再结晶及织构进行了表征,并讨论了变形不均匀对再结晶行为及织构演变的影响。结果表明:<0002>//TD取向晶粒比<0002>//ND取向晶粒更容易发生变形,结合hcp结构滑移系统的有限性,共同决定了TA5合金板材冷轧变形具有不均匀性的特点。退火早期再结晶在局部应变大的区域快速形核,且变形量越大,形核数量也越多,再结晶后样品的晶粒尺寸也越小。局部应变大的区域在退火早期以“定向形核”机制快速发生再结晶形核并长大,包括少量剩余的严重变形<0002>//TD取向晶粒;同时,其余应变较低的组织在再结晶形核全过程以“应变诱发晶界迁动形核”机制缓慢形核,这两种机制共同作用导致退火后板材的织构弱化,但仍以冷轧态的基面织构为主。硬度变化曲线可以很好的反映再结晶程度;但受织构影响,不同测试面的硬度值存在显著差异,加载轴与晶体c轴之间的夹角越大,硬度值越小。

Recrystallization behavior and texture evolution of cold rolled TA5 titanium alloy during annealing

Electron backscatter diffraction(EBSD) was used to characterize the grain size, recrystallization and texture of cold-rolled and annealed TA5 titanium alloy plates, the effects of deformation non-uniformity on recrystallization behavior and texture evolution were discussed. The results show that <0002>//TD-oriented grains are more prone to deforming than <0002>//ND-oriented grains, combined with the limited-slip system of hcp structure, which jointly determine the non-uniformity of cold-rolled deformation of TA5 alloy plates. In the early stage of annealing, the recrystallization rapidly nucleates in the high-stored-energy regions, and the greater the deformation, the more nucleation number, and the smaller the grain size of the sample after recrystallization. The recrystallized grains rapidly complete nucleation through the "oriented nucleation" mechanism in high-stored-energy regions during the early stage of annealing and then grow, including a small amount of residual severely deformed <0002>//TD-oriented grains. At the same time, the recrystallized grains nucleate slowly through the "strain-induced boundary migration" mechanism in the regions with low-stored-energy during the entire recrystallization process. These two mechanisms work together to weaken the texture of the annealed plate, but the cold-rolled state basal texture is still dominated. The hardness curve can well reflect the degree of recrystallization, however, the hardness values of different test surfaces affected by the texture are significantly different. The larger the angle between the loading axis and the crystal c axis, the smaller the hardness value.