Enhancement of strength and ductility in Zr-based bulk amorphous alloys by precipitation of quasicrystalline phase

The crystallization mode of the Zr-Al-Ni-Cu amorphous alloys is found to change from a single stage to two stages on adding Ag or Pd. Furthermore, the first-stage exothermic reaction is found to result from the precipitation of nanoscale icosahedral particles in the size range of 20 to 50 nm. The precipitation is found to occur with high nucleation and low growth rates in a polymorphous mode for the Ag-containing alloys and a diffusion-controlled mode for the Pd-containing alloys. These alloys with a mixed nanoscale structure exhibit enhanced strength and ductility as compared with those for the corresponding amorphous single phase alloys. The findings of the dispersion strengthening as well as the dispersion ductilization arising from the finely dispersed icosahedral entities promise opportunities to fabricate new bulk nonequilibrium phase alloys.