Formation of quasicrystals and amorphous-to-quasicrystalline phase transformation kinetics in Zr₆₅Al_7.5Ni₁₀Cu_7.5Ag₁₀ metallic glass under pressure

The effect of pressure on the formation of quasicrystals and the amorphous-to-quasicrystalline phase transformation kinetics in the supercooled liquid region for a Zr₆₅Al_7.5Ni₁₀Cu_7.5Ag₁₀ metallic glass have been investigated by in situ high-pressure and high-temperature nonisothermal and isothermal x-ray powder diffraction measurements using synchrotron radiation, respectively. It is found that with increasing pressure, the onset temperature for the formation of quasicrystals increases with a slope of 9.4 K/GPa while the temperature interval of the stability and the average grain size of quasicrystals decrease. Atomic mobility is important for the formation of quasicrystals from the metallic glass whereas the relationship of the crystallization temperature vs pressure for the transition from the quasicrystalline state to intermetallic compounds may mainly depend on the thermodynamic potential energy barrier. To study the amorphous-to-quasicrystalline phase transformation kinetics in the metallic glass, relative volume fractions of the transferred quasicrystalline phase as a function of annealing time, obtained at 663, 673, 683, and 693 K, have been analyzed in details using 14 nucleation and growth models together with the Johnson-Mehl-Avrami model. The Avrami exponent was found to be near 1 at all four temperatures, also indicating that atomic diffusion might involve in the amorphous-to-quasicrystalline phase transformation for the Zr₆₅Cu_7.5Al_7.5Ni₁₀Ag₁₀ metallic glass. It is found that the time-dependent transient nucleation is essential for the transformation and different nucleation and growth models have been critically assessed.