Environmental embrittlement of iron aluminides in moisture-containing atmospheres

Conference · Tue Jan 01 00:00:00 EST 1991

OSTI ID:5882493

McKamey, C G; Liu, C T

This paper provides a brief review of recent research on the effect of test environment on room temperature tensile ductility and fracture in FeAl- and Fe{sub 3}Al-based alloys. For more than forty years, iron aluminides have been known to be brittle at ambient temperatures; however, the cause of this brittleness was not identified until recently. The recent study of the mechanical properties of iron aluminides in controlled environments has revealed that brittle fracture and low ductility is probably caused by dynamic environmental embrittlement involving the dissociation of water molecules at the crack tip by aluminum atoms in the alloy and the release of atomic hydrogen. When tested in air, FeAl (36.5% Al) exhibited brittle cleavage fracture and a low ductility of 2.2% at room temperature. The yield stress was found to be insensitive to environment, while the ductility was found to increase to as high as 17.6% when tested in dry oxygen. The fact that the yield strength is insensitive to both ductility and test environment is consistent with the mechanisms of hydrogen embrittlement observed in other ordered intermetallic alloys. Testing in water vapor at gas pressures of 6.7 {times} 10{sup 4} Pa (500 torr) confirmed the low ductility found in air tests, indicating that water vapor is the embrittling agent in iron aluminides. Fe{sub 3}Al also showed environmental embrittlement at room temperature, although the degree of sensitivity was less, presumably because of its lower aluminum concentration. Consistent with being a chemical effect, the environmental embrittlement in Fe{sub 3}Al was found to be insensitive to whether it had the DO{sub 3} or B2 crystal structure. 66 refs., 5 figs., 3 tabs.

• Research Organization: Oak Ridge National Lab., TN (USA)
• Sponsoring Organization: USDOE; USDOE, Washington, DC (USA)
• DOE Contract Number: AC05-84OR21400
• OSTI ID: 5882493
• Report Number(s): CONF-9106145-1; ON: DE91010149
• Resource Relation: Conference: 1. symposium on environmental effects of advanced materials, San Diego, CA (USA), 19-21 Jun 1991
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
ALUMINIUM ALLOYS
MECHANICAL PROPERTIES
IRON ALLOYS
AMBIENT TEMPERATURE
CONTROLLED ATMOSPHERES
CRACKS
CRYSTAL STRUCTURE
DISSOCIATION
DUCTILITY
EMBRITTLEMENT
ENVIRONMENT
FRACTURE PROPERTIES
INTERMETALLIC COMPOUNDS
MINIMIZATION
MODIFICATIONS
RESEARCH PROGRAMS
WATER
WATER VAPOR
YIELD STRENGTH
ALLOYS
ATMOSPHERES
FLUIDS
GASES
HYDROGEN COMPOUNDS
OXYGEN COMPOUNDS
TENSILE PROPERTIES
VAPORS
360103* - Metals & Alloys- Mechanical Properties