变形区形状参数对钽板组织均匀性的影响

Influence of Roll Gap Geometry on Through-Thickness Uniformity of Texture and Microstructure in Clock-Rolled Tantalum

通过控制每道次的轧制压下量,获得了两组轧制变形区形状参数,对高纯钽板进行周向轧制,得到了70%变形量的样品,并对样品进行了真空退火处理(1050℃/1 h)。应用X射线衍射(XRD)技术测量了轧制样品表面层与中间层的宏观织构,结合背散射电子衍射(EBSD)技术表征了轧制样品沿厚度方向上的变形组织与微织构,以及退火态样品的显微组织与织构。结果表明:大的变形区形状参数(2.01~3.29)在轧板表面引入了明显的剪切应变,沿钽板厚度方向易产生严重的织构梯度,钽板表面层形成{hkl}<110>织构以及{100}<uvw>织构,中间层形成强烈的{111}<uvw>织构。较小的变形区形状参数(1.67~2.28)有利于产生均匀变形,可以有效弱化中间层的{111}<uvw>织构,增强{100}<uvw>织构。轧制组织中增强的{100}<uvw>织构可以抑制{111}<uvw>取向再结晶晶粒的异常长大,对细化显微组织有利。

Two sets of roll gap geometry were designed to manufacture tantalum plates by clock rolling. The final plates had 70% reduction in thickness and were annealed at 1050 ℃ for 1 h in vacuum environment. Through-thickness texture and microstructure in the clock-rolled and annealed samples were investigated by XRD and EBSD techniques. XRD measurements were conducted on surface layer and center layer （containing rolling direction and transverse direction, RD-TD）, and EBSD detections were carried out on the upper region and the center region in longitudinal plane （containing rolling direction and normal direction, RD-ND）. The results show that shear strain is readily produced in surface layer with larger roll gap geometries （2.01-3.29） and severe texture gradient exists through the thickness of the plate. Weak {hkl^llO） and {100}（uvw） textures are formed in the surface layer, while strong {lll}（uvw） texture is developed in the center layer. With relatively small roll gap geometries （1.67-2.28）, homogeneous deformation can be obtained and the strong {111}（uvw） texture in the center layer is largely weakened. At the same time, {100}（uvw） texture is enhanced both in the surface layer and the center layer. Such texture can restrain abnormal growth of {111}（uvw） grains during recrystallization.