Temperature dependent lattice misfit and coherency of Al 3 X ( X = Sc , Zr , Ti and Nb ) particles in an Al matrix

The lattice coherency and critical radii for Al3X precipitates in an aluminum matrix were computed using firstprinciples methods. From density functional perturbation theory and the quasi-harmonic approximation, the unit cell parameters as a function of temperature were determined for Al3Sc, Al3Zr, Al3Ti, and Al3Nb in the L12 structure, and for Al3Ti and Al3Nb in their more stable DO22 structures. From these data the lattice misfit and critical radii were determined. It was found that Al3Sc and Al3Zr behave similarly, with increasing critical radii and decreasing misfit as a function of temperature, while Al3Ti and Al3Nb behaved oppositely. Furthermore, the DO22 phases showed uniformly poor lattice coherence and very small critical radii. Superior alloy properties in Al/Al3X systems are suggested to require stabilization of the L12 phase in the precipitated particles.