Oxidation behavior of Cr-Cr{sub 2}Nb alloys

Oxidation of hypoeutectic Cr-Cr{sub 2}Nb alloys containing 6 and 12% Nb at 950 C resulted in formation of a multiproduct scale consisting of a continuous Cr{sub 2}O{sub 3} outer layer and an inner region of discrete CrNbO{sub 4} products interspersed with Cr{sub 2}O{sub 3}. Overall oxidation behavior resembled that of Cr as reactions with the Cr-rich phase tended to dominate. Oxidation resistance, in terms of reaction kinetics and scale adherence, increased with increasing volume fraction of the Cr-Cr{sub 2}Nb eutectic phase. A model for the oxidation of these alloys based on the growth of Cr{sub 2}O{sub 3} on the Cr-rich matrix regions and the formation of a slower growing CrNbO{sub 4} on the Cr{sub 2}Nb-enriched phase can qualitatively explain the development of the multiproduct scale and the observed gravimetric and spallation results. Possible microstructural/compositional modifications to improve oxidation resistance are suggested