MECHANICAL PROPERTIES OF INTERMETALLIC COMPOUNDS BETA-LITHIUM-ALUMINUM AND BETA-LITHIUM-INDIUM

The mechanical properties of the NaTl-type intermetallic compounds (beta)-LiAl and (beta)-LiIn were studied via internal friction, microhardness and compression experiments. The configurations and the energies of antiphase boundaries and dislocations in both compounds were theoretically investigated. The defect structure of (beta)-LiIn was characterized via lattice parameter and bulk density measurements.; The APB in the NaTl structure is associated with wrong next-nearest neighbors. Unit dislocations (a/2)<110> and their dissociated superdislocations are the most stable dislocations and the slip system {lcub}110{rcub}<110> is the most probable slip system in both LiAl and LiIn.; Internal friction decreased and room-temperature hardness increased with incresing Li content in (beta)-LiAl. Vacanies in the Li sublattice did not show a strengthening effect. Impedance in dislocation motion was afforded mainly by lithium antistructure defects in the Al sublattice. The ductile-brittle transition temperature and the yield strength increased with increasing Li composition; these results were correlated with the defect structure of (beta)-LiAl. The magnitude of the activation volumes was small and independent of Li composition. The Peierls process is the most probable rate-controlling deformation mechanism in (beta)-LiAl.; The compositional dependence of experimental density data of (beta)-LiIn did not fit the theoretical density calculations for several single-defect models from lattice parameter data. Rather, the defect structure of (beta)-LiIn was characterized by the coexistence of two types of defects, similar to the defect structure of (beta)-LiAl.; (beta)-LiIn was found to be more ductile than (beta)-LiAl. The compositional dependence of room-temperature hardness, ductile-brittle transition temperature and the yield strength of (beta)-LiIn was observed to be similar to that of (beta)-LiAl, and was correlated with the defect structure. LiIn deformed at low temperatures showed similarities with LiAl in the magnitude and the stress dependence of the activation volumes, thus suggesting Peierls process as the rate-controlling deformation mechanism. Grain-boundary sliding, that was observed in LiIn specimens deformed at high temperatures, became more important in the plastic deformation of LiIn at temperatures above about 300(DEGREES)C.