Oxidation kinetics and microstructure of V-(4-5) wt% Cr-(4-5) wt% Ti alloys exposed to air at 300-650 C

We conducted a systematic study to determine the effects of time and temperature of air exposure on the oxidation behavior and microstructure of V-4Cr-4Ti and V-5Cr-5Ti alloys. All samples were from 1 mm thick cold-rolled sheets, and each was annealed in vacuum at 1050 C for 1 h prior to high-temperature exposure. Different samples from each alloy were heated in ambient air at 500 C for times ranging from 24 to ∼2000 h, and in a thermogravimetric analysis (TGA) apparatus at temperatures ranging from 300 to 650 C. Models describing the oxidation kinetics, oxide type and its thickness, alloy grain size, and depth of oxygen diffusion in the substrate alloy were determined for the two alloys and compared. The results showed that the oxide layers that formed on the surfaces of both alloys in air at 300-650 C are protective, and that the V-5Cr-5Ti alloy is slightly more oxidation-resistant than the V-4Cr-4Ti alloy. (orig.)