LATTICE INSTABILITY ANALYSIS OF A PROTOTYPE INTERMETALLIC SYSTEM UNDER STRESS

The unstable structural responses of a model intermetallic lattice to hydrostatic and uniaxial loadings have been determined by elastic stability analysis and molecular-dynamics simulations. Two crystalline phases of Ni 3Al, the naturally occurring L12 and a hypothetical D022, are analyzed to correlate the effects of structural symmetry with stress-induced lattice deformations. Under isotropic expansion, the former fcc lattice develops extensive cavitation and amorphization at critical isotropic tensile loading, whereas the latter, a tetragonal lattice, shows cleavage behavior. These qualitative differences do not appear in the elastic stability analysis. Both phases show similar responses to uniaxial tension. In all cases critical strains for lattice instability predicted on the basis of elastic stiffness coefficients are found to be in good agreement with direct simulations. © 1995 American Institute of Physics.