Ti-rich precipitate evolution in vanadium-based alloys during annealing above 400 °C

We have assessed the plate-like TiO precipitate evolution in V-4Ti and V-4Ti-4Cr alloys during isochronal annealing above 400 degrees C, by combining Vickers hardness, positron lifetime and coincidence Doppler broadening measurements. Our results reveal the formation of additional TiO precipitates in both alloys at temperatures of 450-600 degrees C in both alloys. The implanted positrons become trapped at the nm-thick TiO/matrix interface, and act as effective probes of the concomitant annealing of vacancies taking place inside the TiO precipitates above 550 degrees C in V-4Ti alloy. The presence of Cr in the ternary alloy not only retards the recovery of dislocations, but also enhances the oxygen diffusivity and therefore decreases the vacancy content in the TiO precipitates. These results will impact the expected alloy stability and capacity to bind light elements in the operational temperature window of these alloys for fusion reaction applications. (C) 2017 The Authors. Published by Elsevier B.V.