A critical examination of pure tantalum processed by high-pressure torsion

Tantalum, a common refractory metal with body-centred cubic (BCC) crystalline structure, was processed by high-pressure torsion (HPT) at room temperature through different numbers of rotations. Significant grain refinement and high strength were achieved with a reduction in grain size from similar to 60 mu m to similar to 160 nm and an increase in strength from similar to 200 to > 1300 MPa. Hardness measurements revealed a high level of homogeneity after 10 turns of HPT but the hardness after 10 turns was slightly lower than after 5 turns indicating the occurrence of some recovery. Tensile testing at a strain rate of 1.0 x 10(-3) s(-1) gave high strengths of similar to 1200 MPa but little or no ductility after processing through 1, 5 and 10 turns. The introduction of a short-term (15 min) anneal immediately after HPT processing led to significant ductility in all samples and a reasonable level of strength at similar to 800 MPa. (C) 2015 Elsevier B.V. All rights reserved.