An unusual phase transformation during mechanical alloying of an Fe-based bulk metallic glass composition

Mechanical alloying of an Fe-based bulk metallic glass composition (Fe60Co8Zr10Mo5W2B15) was conducted starting from blended elemental powders. A supersaturated solid solution of all the alloying elements in Fe has formed in the initial stages of milling. This α-Fe phase became amorphous on subsequent milling up to 20-30 h. Further milling, unexpectedly, led to primary crystallization of the amorphous phase resulting in the formation of an (α-Fe)′ phase with a slightly smaller lattice parameter (and lower solute content) than that in the early stages of milling. External annealing of the amorphous phase powder at 700 °C for 1 h led to complete crystallization of the amorphous phase into a mixture of phases including α-Fe, ZrFe2, Fe2B, Fe3B, MoB2, FeMo2B2, and at least another unidentified phase. Possible reasons for such an unusual amorphous → crystalline transformation on milling in the bulk metallic glass composition are discussed and it was shown that this transformation is due to the combination of defect-assisted diffusion and a slight rise in the powder temperature.