Influence of roll gap geometry on through-thickness uniformity of texture and microstructure in clock-rolled tantalum

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} and {100} textures are formed in the surface layer, while strong {111} 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} texture in the center layer is largely weakened. At the same time, {100} texture is enhanced both in the surface layer and the center layer. Such texture can restrain abnormal growth of {111} grains during recrystallization.