Mechanism of mechanical crystallization of amorphous Fe-Mo-Si-B alloy

Crystallization processes of an amorphous (Fe_0.99,Mo_0.01)₇₈Si₉Bi₁₃ alloy induced by mechanical milling and annealing at pressures from 0 to 7.0 GPa were studied. It is found that the milling time needed for the crystallization of the amorphous alloy and its crystallization products are related to the milling intensity. The crystallization products are an α-Fe(Mo, Si) disordered solid solution at a lower milling intensity, while at a higher milling intensity they are α-Fe(Mo, Si), Fe-Si-B, and Fe₂B phases. By comparing the mechanical crystallization of the amorphous alloy with its high pressure crystallization, it is suggested that crystallization of the amorphous alloy driven by ball milling results from the simultaneous action of local pressure (4-6 GPa) and local temperature (600-700 K), which are produced by the collision of steel balls. The local pressure decreases the thermodynamic potential barrier of nucleation and increases the diffusion activation energy in the process of mechanical crystallization, leading to that crystallization of amorphous alloy is depressed when the crystallization needs a long-range atomic diffusion and is promoted when the crystallization needs atomic diffusionless or short-range diffusion. The local temperature plays the same role in the mechanical crystallization as the annealing temperature in the thermal crystallization.