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 ~60 m to ~160 nm and an increase in strength from ~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  10 -3 s -1 gave high strengths of ~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 ~800 MPa.

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The precipitation of rx phase during ageing was investigated in the near-� titanium alloy Ti-17 consid ering either a fully �metastable initial microstructure or a 35% r:J.primary + 65% �metastable initial micro structure. ln-situ electrical resistivity and high energy X-ray diffraction measurements revealed the influence of the initial microstructure, with different rx morphologies (size and distribution of rxprimary), as well as the heating rate on the precipitation sequences and kinetics following the decomposition of the �-metastable phase. Various amounts of metastable phases (Wisothermal and rx"1sotherma1) precipitate in temperature ranges that increase with the heating rate. From temperatures about 500 °C, the ortho rhombic rx"isothermal structure evolved towards the hexagonal close-packed rx as temperature increased. SEM microstructure characterisations showed that slow heating rates promoted a fine and dense rx precipitate distribution through the formation of Wisothermal and/or rx"isothermal, leading to higher hardness values. A higher heating rate restricted the precipitation of rx"1sotherma1 and shifted to the one of rx at a higher temperature, leading to coarser precipitates. Furthermore, precipitation kinetics of rx";sotherma1/rx were quicker considering an initial intragranular rx precipitation as compared to rx colonies.