Effect of alloying, rapid solidification, and surface kinetics on the high-temperature environmental resistance of niobium. Annual technical report, November 1985-January 1986

Technical Report · Fri Feb 20 04:00:00 EST 1987

OSTI ID:6481422

Perkins, R A; Chiang, K T; Meier, G H

A model derived from first principles for the transition from internal to external oxidation was shown to be applicable to the oxidation of alloys. The feasibility of forming protective alumina scales by the selective oxidation of aluminum at greatly reduced Al contents was demonstrated. The critical NAL for the transition was lowered to between 25 and 30 at.% AL by the balanced addition of elements that simultaneously reduce NO(s) and DO and increase DAL in the alloy. The model indicates that a low DAL is the major factor limiting the selective oxidation of Al and that an increase of about 6 orders of magnitude would be required to effect a transition to external scale information at 1100 C. A major increase in DAL was achieved by adding Ti to increase the solubility of Al in bcc Nb. This resulted in formation of alumina at an NAL of 0.4 in air at 1400 C. By adding Cr and V to reduce NO(s) and DO, the critical NAL was reduced further to between 0.25 and 0.3 at 1400 C. An alloy of niobium-29 titanium-38 aluminum-3 chromium-4 vanadium (at.%) formed highly protective alumina in air at 1400 C. The ability to form alumina decreased as temperature decreased due to the high activation energy of alumina formation and rapid kinetics of transient oxidation. Further modification of both composition and alloy structure is needed.

• Research Organization: Lockheed Missiles and Space Co., Inc., Palo Alto, CA (USA). Research and Development Div.
• OSTI ID: 6481422
• Report Number(s): AD-A-179245/6/XAB; LMSC/F-195926
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
360105* -- Metals & Alloys-- Corrosion & Erosion
ACTIVATION ENERGY
ALLOYS
ALUMINIUM ALLOYS
CHEMICAL REACTIONS
CHROMIUM ALLOYS
ELEMENTS
ENERGY
FEASIBILITY STUDIES
HIGH TEMPERATURE
KINETICS
METALS
NIOBIUM
NIOBIUM ALLOYS
OXIDATION
PHASE TRANSFORMATIONS
SOLIDIFICATION
SOLUBILITY
SURFACES
TITANIUM ALLOYS
TRANSIENTS
TRANSITION ELEMENTS
VANADIUM ALLOYS