STUDIES OF THE OXIDATION AND CONTAMINATION RESISTANCE OF BINARY NIOBIUM ALLOYS

A study of the effects of binary alloying additions on the oxidation and contamination resistance of niobium has been conducted.The alloys contained up to 35 a/o titanium, chromium, and zirconium, 25 a/o vanadium, molybdenum, tantalum, and tungsten, and 5 a/o beryllium, boron, cobalt, iron, manganese, nickel, and silicon.The oxidation and contamination studies were conducted in air at 600, 800, and 1000 C. Four elements, titanium, vanadium, molybdenum, and chromium, improved oxidation resistance.The concentrations for optimum oxidation resistance at 1000 C were 25 a/o titanium, 10 a/o vanadium, 5 a/o molybdenum, and 25 a/o chromium.Titanium was most effective in reducing the rate of oxidation; at 600 to 1000 C, the niobium-25 a/o titanium alloy oxidized one-tenth to one-twentieth as rapidly as pure niobium.Contamination was investigated by hardness-penetration measurements on all oxidized alloys except those containing beryllium or boron.Zirconium and titanium markedly reduced the depth of oxygen contamination resulting from exposure to air.Diffusion coefficients for oxygen in the niobium binary alloys were calculated, and related by activationenergy plots where possible.Zirconium, titanium, chromium, and vanadium were most effective in reducing oxygen diffusion into niobium.