The influence of carbon on precipitation of alpha in Ti-5Al-5Mo-5V-3Cr

The effect of carbon-doping on the ageing response of solution heat-treated and quenched Ti-5Al-5Mo-5V-3Cr, a metastable beta-Ti alloy, has been characterised using scanning and transmission electron microscopy, and microhardness testing. Alloys containing 0-0.1 wt% added carbon were processed and parameters including solution temperature, ageing temperature, time and heating rate were varied to study the resultant microstructural evolution. Results show that small carbon additions have a significant effect on alloys that were beta-solutionised and subsequently aged at 500-600 degrees C, both refining and homogenising the precipitating alpha phase. Importantly, carbon reduces the tendency for coarse alpha to form at grain boundaries and, at lower ageing temperatures, strongly affects formation of isothermal omega. It is also demonstrated that considerable a refinement in undoped alloys can be achieved through slow or step heating. It appears that the responsible refinement mechanisms resulting from carbon-doping are different from those resulting from slower heating. (C) 2010 Elsevier B.V. All rights reserved.