DIFFUSION OF OXYGEN IN VANADIUM AND ITS ALLOYS

Diffusion coefficients of oxygen have been measured in vanadium and dilute substitutional alloys (V-1Si, V-0.1Al, V-0.1B, V-5Cr, V-5Fe, V-5Mo, V-5Nb, V-5Ti and V-3Ti-2Si where the compositions are in approximate atomic per cent) over the temperature range 489-774 K. The ''O was injected by ion implantation. The diffusion penetration profiles were measured by the O-16(d,p)O-17 nuclear reaction method. The temperature dependence of the oxygen diffusivity in vanadium is expressed as D = (1.3(-0.5)+0.9) x 10(-6) exp (-121.6+/-2.5 kJ mol-1/RT) m2s-1. The addition of silicon and aluminium hardly affects oxygen diffusion, while the addition of iron, niobium and boron decreases the diffusivity by 20-70%, and the addition of chromium and molybdenum decreases the activation energy by 10-15%. The most significant alloying effect is observed in V-3Ti-2Si and V-5Ti alloys. The diffusivity in V-5Ti alloy is about two orders of magnitude lower than that in vanadium. This effect is interpreted as evidence for a trapping effect due to titanium; the binding energy is estimated to be about 52 kJ mol-1.