Nanocrystallization of Al-Ni-Y and Al-Ni-Nd metallic glasses

Crystallization behavior and microstructural development during annealing of Al90Ni6Nd4 and Al85Ni5Y10 glasses were investigated in detail by quantitative TEM. Isothermal annealing for various periods at temperatures between 140 degrees C and 250 degrees C lead to partially nanocrystalline microstructures consisting of a fine dispersion of alpha-Al nanocrystals embedded in an amorphous matrix. The Al85Ni5Y10 glass exhibits a higher thermal stability than Al90Ni6Nd4 glass. Nucleation was studied by crystallization statistics of partially crystallized glasses by fitting measured crystal size distributions. Crystallization statistics revealed that the alpha-Al phase forms by transient heterogeneous nucleation with nucleation rates in the order of 10(20) - 10(21) m(-3)s(-1). The nanocrystal growth proceeds rapidly at the beginning, but was found to slow down probably due to the formation of a RE-rich diffusion barrier between the alpha-Al crystals and the matrix; Nd seems to be even more effective in slowing down the growth than Y.