OXIDATION OF Nb-Zr ALLOYS

The effect of Zr on the oxidation resistance of Nb-- Zr alloys containing 0.25, 0.5, 1.5, 10, 15, 20, 25, 30, 40, or 50% Zr was investigated. Alloy specimens were obtained by compacting ZrI/sub 2/ and 99.78% pure Nb and melting the compacts in an unconsumable-electrode arc furnace in an Ar atmosphere under a pressure of 250 mm Hg. Specimens were oxidized in air at 1600, 1120, and 1260 deg C for 1, 2, 3, 5, and 10 hrs. Zr at contents of 6.25 to 10% was found to accelerate oxidation; however, a further increase of Zr content up to 56% lowers the oxidation rate continuously. An alloy with 50% Zr oxidizes at a rate of approximates 10, 18, or 25 mg/cm/sup 2/ hr at 1000, 1100, or 1200 deg C, respectively. The oxidation of alloys with 40 and 50% Zr at 1000 and 1100 deg C follows a nearly parabolic rate, which indicates that the oxide film has a protective ability. At 1200 deg C the oxidation rate is linear. The scale of alloys with up to 25% Zr is loose and separates from the metal. In an alloy with 50% Zr, the scale adheres tightly to the metal.more » A thin sub-layer please delete the above abstract no. 29291====« less