Three vanadium alloys, VANSTAR-7* * VANSTAR is a general term denoting a series of vanadium-base alloys developed by Westing-house Electric Corporation., VANSTAR-9, and V-20Ti were examined after 500 and 1500 h exposure to sodium flowing at 5 ft/sec, and containing < 10 p.p.m. oxygen over the temperature range 675 °-800 °C. In all cases, weight gains were observed, but, the V-20Ti alloy gained approximately three times more weight than the VANSTAR alloys. The results appeared to fit the parabolic rate law, Δ/dw2 = Kpt, and the observed weight gains were due to the transport and solution of nitrogen, carbon, and oxygen. The variation of the parabolic rate constant with temperature follows an Arrhenius-type relationship. Diffusion coefficients of 1·1 × 10-11, 2·5 × 10-12, and 2·5 × 10-12 cm-2 sec-1 for nitrogen, carbon, and oxygen in the VANSTAR-9 alloy were calculated from analytical data. All alloys showed surface hardness increases due to interstitial absorption, and, in the case of the VANSTAR alloys, considerable hardening was observed away from the surface regions. The bend ductile-brittle transition temperatures were increased after corrosion, and considerable reductions were noted in room-temperature tensile ductility. However, after 1500 h exposure to sodium, samples of the VANSTAR alloys still retained more than adequate ductility at ~700 °C, for cladding applications. © 1969.
