A MICROMECHANISM FOR CRYSTALLIZATION OF AMORPHOUS-ALLOYS .1. AN INSITU TEM OBSERVATION

The dynamic crystallization process in a two-dimensional (2D) amorphous Ni-P foil was investigated by the use of in situ transmission electron microscopy (TEM) observation. On annealing the amorphous foil, it has been found that the clusters of the Ni3P phase were formed in the amorphous matrix with random orientations before the crystals nucleated and grew. During the crystal growth process, transformation of the clusters was found to be in the form of shearing deposition onto the crystal front. A new micromechanism for universal crystallization processes was proposed based on experimental results of the 2D crystallization. It is composed of two processes: (i) formation and growth of precursory ordered clusters in amorphous matrix; (ii) crystal nucleation and growth which involve atoms jumping and clusters shearing deposition or combination. The new mechanism is discussed with respect to the existence of ordered clusters and their effects on the crystallization kinetics.