Processing and characterization of rapidly quenched Ti-based alloys: Influence of solidification rate on the as-quenched structures

From technological viewpoint, icosahedral Ti-Zr-Ni phase may give challenging opportunities as novel hydrogen storage and hydride battery. Nevertheless, from the structural standpoint, the phase selection criterion as function of solidification route remains unclear. A series of Ti45Zr38Ni17 alloys, known to provide stable and well-ordered quasicrystals, was produced by planar flow casting using different processing parameters. From structural characterization, it appears that, at high cooling rate, i.e. high wheel speeds, or for the highest temperature of the melt, the as-quenched sample exhibits a mixture of nanoscale β and amorphous phases. The icosahedral phase precipitates when decreasing the wheel speed, from lower temperatures of the melt or after annealing a crystallized amorphous matrix. The reproducible formation of quasicrystals, observed in the amorphous matrix containing β particles, corroborates the competition between icosahedral and body-centered cubic (bcc) phases during the solidification process. These results are promising since it could be possible to control volume fractions of these two phases by choosing well-fitted thermal treatments so that quasicrystals mechanical properties should be improved by dispersion of a stable bcc phase.