Precipitation and Ostwald Ripening in Dilute Al Base-Zr-V Alloys

摘要

The coarsening rates of both cubic and tetragonal aluminum zirconium precipitates in aluminum were measured. The tetragonal Al3Zr coarsened 16 times faster than the cubic modification in keeping with the fact that the latter is coherent and coplanar with the matrix while the former forms a semi-coherent interface with the matrix giving a larger interfacial energy. Partial substitution of vanadium zirconium reduced the precipitate-matrix mismatch for both phases and slowed both coarsening rates as well as retarded the cubic to tetragonal transformation. Reducing strain and interfacial energy no doubt is the origin of this effect. Since the cubic particles are spherical, their volume fraction is small, and the coherency strains are small, this would appear to be an ideal system for testing the Lifshitz-Sylozov-Wagner theory of diffusion controlled Ostwald ripening. While the theory seems to hold, the calculated diffusivity of Zr in Al is much higher than the value reported in the literature. Because of the low coarsening rates of the dispersed particles, the aluminum zirconium vanadium system shows promise as the basis for a high temperature Al alloy.