Recovery and recrystallization in rolled tantalum single crystals

Abstract

The recovery and recrystallization behavior of rolled tantalum single crystals having initial orientations of (001) [110], (112) [110] and (111) [110] has been studied. Each crystal developed a simple, single component texture upon rolling. The texture became more diffuse and the local lattice curvature more intense as the rolling plane deviated from (001) towards (111). The (001) [110] and (112) [110] crystals formed a uniform dislocation array and polygonization occurred on annealing. No recrystallization of the (001) [110] crystal took place at temperatures up to 1673 K. A few randomly-oriented recrystallized grains were nucleated in the (112) [110] crystal but these may have been artificially nucleated. Only the (111) [110] crystal reoriented during rolling; it also formed a cellular dislocation microstructure. This orientation was the only one to recrystallize easily, primarily because of the large lattice curvature. The recrystallized grains could be related to the deformation texture by a rotation of 23 to 24 deg about a common <111> direction that was parallel to the normal direction of the sheet. The nature of the misorientation spread after rolling may have dictated this relation as a compromise to the one usually found in bcc materials,viz. 25 to 30 deg rotation about a common <110> axis. Also, wide dislocation cell size distributions were noted in the (111) [110] crystal. The cell size distributions were log normal in nature. Subgrain growth was very much more rapid in this crystal. There was a large discrepancy between the observed subgrain growth and that predicted theoretically by the coalescence model.