Effects of doping elements on oxidation properties of low-activation vanadium alloys

V-(4-5)Ti-(4-5)Cr type alloys doped with Si, Al and Y were studied in an ef fort to develop oxidation-proof vanadium alloys. In order to clarify the ef fects of the doping elements, the oxidation behavior of V-4Ti-Cr, V-4Ti-4Cr -0.5Si, V-4Ti-4Cr-0.5Al and V-4T-4Cr-0.5Y alloys was studied. Thermogravime tric analysis (TGA) experiments in dr at 400, 500, 620 and 650 degreesC and exposure to air, helium and low oxygen partial pressure atmospheres at 500 degreesC for 250 h were carried out for each alloy. After exposure, measur ement of mass gain and tensile tests were performed to study the influence of the exposure atmosphere on each alloy. After exposure to helium atmosphe re 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) P a. Tensile testing at room temperature showed that the V-4Ti-4Cr-0.5Si allo y has the highest ultimate tensile stress, and V-4Ti-4Cr-0.5Y has the highe st total elongation after exposure for all the atmospheres. The results of the TGA experiments in air show that yttrium doping is more effective at hi gher-temperature exposure. The V-4Ti-4Cr-0.5Y alloy has the highest oxidati on-resistance at 620 degreesC in all the alloys. The TGA data fit the parab olic oxidation law, especially in the first stage of oxidation time up to 3 0 h.