Crystallization behaviour and nanocrystalline microstructure evolution of a Zr57Cu20Al10Ni8Ti5 bulk amorphous alloy

Crystallization behaviour and microstructure evolution of a Zr57Cu20Al10Ni8 Ti5 bulk amorphous alloy were studied under different annealing conditions. Devitrification of this amorphous alloy results in a fully nanocrystalline microstructure or a microstructure consisting of nanocrystals embedded in an amorphous matrix. The transformation to the nanocrystalline microstructu res is attributed to a low crystal growth rate and an increasing crystalliz ation temperature of the residual amorphous phase as the crystallization pr oceeds. The characteristic crystallization behaviour of this amorphous allo y is discussed. The rate of crystallization becomes very sluggish after ini tial crystallization during isothermal annealing. The crystallization kinet ics does not fit the conventional Johnson-Mehl-Avrami model. These features can be related to a component partition between the primarily precipitated crystals and the residual amorphous phase which leads to an increasing cry stallization temperature of the residual amorphous phase and a significant change of the nucleation and crystal growth rates. Cooling rate of casting may affect the short range order of the liquid alloy or phase separation an d consequently the precipitation from the amorphous alloy.