冷轧高纯钽板退火过程中微观组织及织构演变的梯度效应

Gradient of Microstructure and Texture Evolution of Cold Rolled High Purity Tantalum Plate During Annealing Process

本研究综合采用电子背散射衍射(EBSD)、X射线衍射(XRD)和显微硬度等技术,系统研究了87%周向轧制钽板在1 323K下经5min、10min、30min、60min、90min和120min退火后沿厚度方向的显微组织演变规律。实验结果表明,中心区域的形变组织率先产生再结晶晶核且该区域的形核过程主要由大角度晶界形核机制主导,而近表面区域的形核则由亚晶形核机制发挥主要作用。其次,中心区域比近表面区域表现出更快的再结晶动力学,再结晶完成后,中心{111}〈uvw〉织构(〈111〉∥ND(板法向))强度高,而近表面{100}〈uvw〉织构(〈100〉∥ND)强度相对较高。变形钽板中心区域的{111}〈uvw〉织构强度高,储存能高且晶粒内部分裂严重,所以较早发生再结晶;而近表面区域{100}〈uvw〉织构强度高且晶粒内部分裂程度相对较小,储存能低,使得回复孕育期较长。由此导致再结晶组织和织构沿厚度方向上产生梯度效应。

135°clock-rolled Ta plates with 87%thickness reduction were annealed at 1 323 K for different time(5 min,10 min,30 min,60 min,90 and 120min,respectively).The through-thickness microstructure evolution was systematically studied by electron back-scattered diffraction(EBSD),X-ray diffraction(XRD)and microhardness techniques.It was revealed that the recrystallization nucleus preferred to appear in the central region dominated by high angle boundary nucleation mechanism in this process.However,subgrain nuclear mechanism played an important role in the nucleation of near surface zone.Besides,the center area showed faster recrystallization kinetics than the near surface area,and after recrystallization,the center of{111}〈uvw〉(〈111〉∥ND)texture was stronger whereas the near surface possessed much more{100}〈uvw〉(〈100〉∥ND).Such a difference was mainly contributed to the strong{111}texture of the center layer possessing high stored energy as well as its severe fragmentation of internal grain.On the contrary,{100}texture accounting for a large proportion of the near surface zone,which contained lower stored energy and small internal misorientations,led to a longer incubation period for recrystallization nucleation.As a result,the recrystallization texture gradient along the thickness direction appeared.