MICROSTUCTURAL EVOLUTION AND MECHANICAL-PROPERTIES OF RAPIDLY SOLIDIFIED AL-ZR-V ALLOYS AT HIGH-TEMPERATURES

Aging studies of three melt spun, AlZrV alloys showed that precipitation of the metastable Ll2 phase occurs prior to that of the equilibrium phases, Al10V and Al3Zr(D023). The precipitation mechanism of the Ll2 phase can be either continuous or discontinuous. The former is favored by decreasing the value of the Zr/V ratio in the l12 phase precipitate or by increasing the aging temperature. Decreasing the Zr/V ratio also makes it easier to obtain a supersaturated solid solution during melt spinning. Coarsening of the spherical Ll2-structured Al3(Zr0.25V0.75) particles was studied at 425, 450 and 500°C. The activation energy calculated from the particle coarsening kinetics is close to that for diffusivity of Zr in the Al matrix, suggesting that volume diffusion of Zr is the rate controlling mechanism for the Ostwald ripening of the Ll2-structured Al3(Zr0.25 V0.75). The Ll2 phase precipitate in extruded samples of this alloy grew slowly at 425°C, close to the rate measured in the melt spun ribbon. Dislocation cross-slip occurred inside the Ll2 phase particles from a (111) plane to a {100} plane during creep. © 1990.