Effects of Doping Elements on Oxidation Properties of Low-Activation Vanadium Alloys

Abstract

V-(4-5)Ti-(4-5)Cr type alloys doped with Si, Al and Y were studied in an effort to develop oxidation-proof vanadium alloys. In order to clarify the effects of the doping elements, the oxidation behavior of V-4Ti-4Cr, V-4Ti-4Cr-0.5Si, V-4Ti-4Cr-0.5Al and V-4T-4Cr-0.5Y alloys was studied. Thermogravimetric analysis (TGA) experiments in air at 400, 500, 620 and 650°C and exposure to air, helium and low oxygen partial pressure atmospheres at 500°C for 250 h were carried out for each alloy. After exposure, measurement of mass gain and tensile tests were performed to study the influence of the exposure atmosphere on each alloy. After exposure to helium atmosphere with oxygen partial pressure P O2 = 20 Pa gave a smaller mass gain than that by the low oxygen partial pressure atmosphere of P O3 = 1.3 x 10 -4 Pa. Tensile testing at room temperature showed that the V-4Ti-4Cr-0.5Si alloy has the highest ultimate tensile stress, and V-4Ti-4Cr-0.5Y has the highest total elongation after exposure for all the atmospheres. The results of the TGA experiments in air show that yttrium doping is more effective at higher-temperature exposure. The V-4Ti-4Cr-0.5Y alloy has the highest oxidation-resistance at 620°C in all the alloys. The TGA data fit the parabolic oxidation law, especially in the first stage of oxidation time up to 30 h.