Explosive crystallization in amorphous CuTi thin films: a molecular dynamics study

Molecular dynamic simulation was used to study mechanism of self-propagating waves of explosive crystallization (devitrification) in the CuTi metallic glass. Processes in thin rectangular samples composed of one to two million atoms were simulated and compared with experimental data. It was shown that the nucleation of primary crystalline clusters occurs homogeneously due to spontaneous fluctuations of atomic structure; the clusters not < 50-100 atoms (similar to 8-10 nm in diameter) have good chance to grow into steady crystalline grain. Self propagating front of crystallization can be initiated locally from one end of the glassy sample; it propagates across the whole sample accompanied by a thermal wave, due to the exothermic effect of devitrification. Temperature rises in the front of this wave from 500 to 550 K up to 665-714 K; the thickness of preheated zone is about 20 nm, the thickness of amorphous-to-crystalline transition zone similar to 1 nm, the propagating velocity is 40 m/s. The uniform heating of the whole sample above 600 K leads to spontaneous nucleation and growth of many crystalline grains, which cause a self-heating of the sample similar to a thermal explosion.