Processing microstructure property relationships in severely deformed tantalum

Bars of as-cast, large grained and highly textured Ta were deformed by multipass equal channel angular extrusion (ECAE) at room temperature to strains of 4.6 through 90 degrees die-angle tooling. The ability of ECAE processing to produce a uniform fine-grained microstructure with homogenous deformation characteristics is investigated. Comparisons of the microstructure and mechanical properties after four consecutive extrusions via route C (180 degrees rotation between passes) and E (2C, 90 degrees rotation then 2C) are made in both the as-worked (submicron-scale grains) and recrystallized (micron-scale grains) states. It is shown that the as-worked grain size levels out at 200-300 nm after four passes. The recrystallized grain size after two to four passes is similar to 10-15 mu m with microstructural uniformity that is dependent on the microstructural uniformity in the starting material. It is also demonstrated that four pass ECAE processing of as-cast large grained BCC materials is not necessarily enough to homogenize texture. A pre-processing step with combined severe plastic deformation and recrystallization improves microstructural uniformity and lessens texture gradients in subsequent deformation processing steps. (c) 2007 Published by Elsevier B.V.