Accession Number : ADA192093

Title :   Effect of Alloying, Rapid Solidification, and Surface Kinetics on the High Temperature Environmental Resistance of Niobium.

Descriptive Note : Technical rept. Jan 87-Jan 88,

Corporate Author : LOCKHEED MISSILES AND SPACE CO INC PALO ALTO CA RESEARCH AND DEVELOPMENT DIV

Personal Author(s) : Perkins, R A ; Meier, G H ; Miller, R A ; Chiang, K T

PDF Url : ADA192093

Report Date : 08 Jan 1988

Pagination or Media Count : 49

Abstract : An improved understanding of factors governing the selective oxidation of aluminum to form continuous alumina scales on modified niobium-aluminum alloys has been established. It has been demonstrated that highly protective alumina scales can be formed on niobium-titanium-chromium-vanadium-aluminum alloys without transient oxidation products at temperatures of 1400 to 1600 C in air. Aluminum content has been identified as the critical factor controlling single layer alumina formation. It also has been shown that the N sub Al(crit) for the formation of a continuous alumina scale is 0.375 - 0.38 at 1400 C, decreasing slightly with increased Nb-Ti ratio in the alloy. A fourth element must be added to niobium-titanium-aluminum for effective alumina formation. It has been established that this element should be from a group that can reduce the solubility-diffusivity at 1400 - 1600 C. Alumina can be formed at 1400 C by substituting V or Ti but a liquid transient oxide is produced. A high rate of transient oxidation relative to alumina formation in this range accelerated transient oxidation and precluded alumina growth instead.

Descriptors :   *ALUMINUM OXIDES, *NIOBIUM, *QUICK REACTION, *SOLIDIFICATION, ACCELERATED TESTING, ALLOYS, ENVIRONMENTS, GROWTH(GENERAL), HIGH RATE, HIGH TEMPERATURE, KINETICS, LAYERS, LIQUIDS, OXIDATION, OXIDES, RESISTANCE, SCALE, SURFACES, TRANSIENTS

Subject Categories : Inorganic Chemistry

Distribution Statement : APPROVED FOR PUBLIC RELEASE