Synthesis of atomistic and continuum modelling of intermetallic alloys

Conference · Tue Jan 01 04:00:00 EST 1991

OSTI ID:5966129

Fu, C L; Yoo, M H

The mechanistic understanding of yield and flow strengths and brittle fracture behavior of ordered transition-metal aluminides has been critically assessed on the basis of quantum mechanical total-energy calculations, and anisotropic elasticity theory of dislocations and cracks. The bonding mechanism is described by the combination of charge transfer (from Al to transition-metals) and strong p-d hybridization effects. The strong ordering behavior of Ni-base aluminides is attributed to the size difference and electrochemical difference between constituent elements. The calculated (and observed) defect structure of NiAl-constitutional vacancies in Al-rich NiAl, and substitutional defects in Ni-rich NiAl-is well correlated with the proposed bonding mechanism and ordering behavior of aluminides. The ground-state elastic constants, various shear fault energies, and cleavage energies are calculated for aluminides of cubic (L1{sub 2} and B2) and tetragonal (L1{sub 0} and D0{sub 22}) structures. The anomalous yield and flow behavior of Ni{sub 3}Al is analyzed by means of symmetry considerations and the interaction torque effect on the mobility of superdislocations subjected to generalized applied stress. The calculation suggests that the elastic shear anisotropy is the major driving force underlying the positive temperature dependence of yield strength. The ideal cleavage strength is determined by the surface electronic structure calculation, and the critical stress-intensity factor for Mode-I crack is obtained using the calculated cleavage energies and elastic constants. The reported cleavage habit planes of (110) for NiAl and (100) for FeAl are interpreted in terms of cleavage energy anisotropy and the orientation dependence of crack-tip plasticity. The mechanism underlying the hydrogen-induced embrittlement effect in FeAl is investigated by first-principles total-energy approach.

• Research Organization: Oak Ridge National Lab., TN (USA)
• Sponsoring Organization: DOE; USDOE, Washington, DC (USA)
• DOE Contract Number: AC05-84OR21400
• OSTI ID: 5966129
• Report Number(s): CONF-9104224-1; ON: DE91011089
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
360103* -- Metals & Alloys-- Mechanical Properties
ALLOY SYSTEMS
ALLOYS
ALUMINIUM ALLOYS
BINARY ALLOY SYSTEMS
BONDING
BRITTLENESS
CLEAVAGE
CRYSTAL STRUCTURE
ELECTRONIC STRUCTURE
EMBRITTLEMENT
FABRICATION
FRACTURE PROPERTIES
HYDROGEN EMBRITTLEMENT
INTERMETALLIC COMPOUNDS
IRON ALLOYS
JOINING
MATHEMATICAL MODELS
MECHANICAL PROPERTIES
MECHANICS
MICROSTRUCTURE
NICKEL ALLOYS
QUANTUM MECHANICS
SHEAR
STRESS INTENSITY FACTORS
TEMPERATURE DEPENDENCE
YIELD STRENGTH