Deformation mechanism of metastable oriented grains in high-purity tantalum under different strain paths

Abstract

High-purity tantalum is used as the sputtering target material for integrated circuits, requiring fine grains and random texture. Understanding different orientation deformation mechanisms, especially the metastable orientation (here {112} crystallographic orientations), is beneficial for controlling the structure of tantalum target materials. This paper employs EBSD and crystallographic calculations to regulate the grain deformation behavior by introducing a reverse strain at 135° clock rolling. The deformation behavior and dislocation density distribution of the metastable oriented grains under different strain paths are quantitatively analyzed. Results show that unidirectional rolling (UR) generates stress concentration, causing an uneven distribution of geometrically necessary dislocation density. The splitting behavior of {112} and {111} grains is promoted, and they have similar deformation behavior in UR process, while the deformation of {100} oriented grains is significantly suppressed. Furthermore, changing the strain path promotes the splitting of {100} grains, and makes the {112} change from the soft orientation to the hard orientation. This change makes it easier to start multi-slipping, resulting in a more uniform deformation. Additionally, crystallographic calculations show that Schmid factor is ineffective in explaining the strain localization problem in BCC metals. However, Schmid factor difference ratio makes it possible to analyze the distribution of dislocation density in local regions through the quantitative calculation of multi-slipping.

Keywords

• Tantalum
• Metastable orientation
• Deformation
• Dislocation
• Strain path