Effect of addition of molybdenum or niobium on creep-rupture properties of Fe sub 3 Al
- Metals and Ceramics Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831-6117 (United States)
Recent alloy development efforts have shown that Fe{sub 3}Al-based alloys can have room temperature tensile ductilities of 10--20% and yield strengths of 500 MPa at temperatures to 600 {degree}C. These property improvements are important for enabling the use of iron-aluminides for structural applications that require their excellent corrosion resistance. New data are presented here from creep-rupture studies on Fe{sub 3}Al and on Fe{sub 3}Al-based alloys containing molybdenum or niobium plus zirconium. Binary Fe{sub 3}Al alloys have low creep resistance, but the addition of 2 at. % Mo or 1% Nb plus 0.1% Zr increases the creep life and reduces the minimum creep rate, with the niobium-containing alloy being the strongest. The improvement in creep life is the result of a combination of factors which include grain boundary strengthening, resistance to dynamic recrystallization during stressing, precipitation strengthening, and changes in the formation and mobility of the dislocation network. Correlation of optical, scanning electron, and transmission electron microscopy data suggests that the intergranular creep failure found in Fe{sub 3}Al after creep testing at 550--650 {degree}C is related to weak high-angle grain boundaries and to formation of subgrain boundary arrays, which reduce the ability of dislocations to glide or multiply to produce matrix plasticity. The addition of niobium/zirconium results in solid solution strengthening effects, as well as the formation of fine MC precipitates (a small amount of carbon is present as a contaminant from the casting process) which strengthen both the matrix and grain boundaries. The result relative to the binary alloy is increased creep-rupture strength and life coupled with a change to a ductile-dimple transgranular failure mode. This suggests that the mechanisms that cause failure during creep can be controlled by macro- and microalloying effects.
- DOE Contract Number:
- AC05-84OR21400
- OSTI ID:
- 7267174
- Journal Information:
- Journal of Materials Research; (United States), Vol. 7:8; ISSN 0884-2914
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
ALUMINIUM ALLOYS
CREEP
RUPTURES
IRON ALLOYS
BINARY ALLOY SYSTEMS
DISLOCATIONS
GRAIN BOUNDARIES
MICROSCOPY
MOBILITY
MOLYBDENUM ADDITIONS
NIOBIUM ADDITIONS
TEMPERATURE RANGE 0400-1000 K
ZIRCONIUM ADDITIONS
ALLOY SYSTEMS
ALLOYS
CRYSTAL DEFECTS
CRYSTAL STRUCTURE
FAILURES
LINE DEFECTS
MECHANICAL PROPERTIES
MICROSTRUCTURE
MOLYBDENUM ALLOYS
NIOBIUM ALLOYS
TEMPERATURE RANGE
ZIRCONIUM ALLOYS
360103* - Metals & Alloys- Mechanical Properties