Electronic, elastic, and fracture properties of trialuminide alloys: Al sub 3 Sc and Al sub 3 Ti
- Metals and Ceramics Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831-6114 (USA)
The electronic mechanism behind the brittle fracture of trialumide alloys is investigated using the full-potential linearized augmented plane-wave (FLAPW) total-energy method within the local density functional approach. To this end, the bulk phase stability, the elastic constants, the anti-phase boundary (APB) energy, the superlattice intrinsic stacking fault (SISF) energy, and the cleavage energy on different crystallographic planes have been determined. A small energy difference (=0.10 eV/unit formula) is found between the DO{sub 22} and L1{sub 2} structures of Al{sub 3}Ti. In general, the trialuminide alloys have large elastic modulus, small Poisson's ratio, and small shear modulus to bulk modulus ratio. An extremely high APB energy (=670 mJ/m{sup 2}) on the (111) plane is found for Al{sub 3}Sc, indicating that the separation between 1/2 {l angle}110{r angle} partials of a {l angle}110{r angle}(111) superdislocation is small. Since the total superdislocation has to be nucleated essentially at the same time, a high critical stress factor for dislocation emission at the crack tip is suggested. The high APB energy on the (111) plane is attributed to the directional bonding of Sc({ital d}-electron)--Al( {ital p}-electron). The same type of directional bonds is also found for Al{sub 3}Ti. In addition, moderately high values of SISF energy (=265 mJ/m{sup 2}) on the (111) plane and APB energy (=450 mJ/m{sup 2}) on the (100) plane are found for Al{sub 3}Sc. The brittle fracture of trialuminide alloys is attributed to the higher stacking fault energies and a lower cleavage strength compared to those of a ductile alloy (e.g., Ni{sub 3}Al). While the (110) surface has the highest surface energy, the cleavage strength (=19 GPa) of Al{sub 3}Sc is found to be essentially independent of the crystallographic planes.
- DOE Contract Number:
- AC05-84OR21400
- OSTI ID:
- 6716713
- Journal Information:
- Journal of Materials Research; (USA), Journal Name: Journal of Materials Research; (USA) Vol. 5:5; ISSN JMREE; ISSN 0884-2914
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
360104* -- Metals & Alloys-- Physical Properties
ALLOYS
ALUMINIUM ALLOYS
CRYSTAL DEFECTS
CRYSTAL STRUCTURE
DENSITY
ELASTICITY
ELECTRONIC STRUCTURE
FRACTURE PROPERTIES
FUNCTIONALS
FUNCTIONS
MECHANICAL PROPERTIES
PHYSICAL PROPERTIES
POTENTIALS
SCANDIUM ALLOYS
STACKING FAULTS
SUPERLATTICES
TENSILE PROPERTIES
TITANIUM ALLOYS
VARIATIONAL METHODS