The Role of Impurities in the Crystallization of Ball-Milled Amorphous Alloys

Abstract

Melt spun amorphous Fe 83 B 17 ribbons were pulverized in a planetary ball mill. Two parallel sets of experiment were made, where the material of the vial made the only difference in the experimental conditions. In the first kind of experiments tungsten carbide balls and vials were used, while in the second series the tungsten carbide balls were put in chrome steel vials. This way the effect of impurities on the mechanically induced crystallization could be studied and distinguished from other possible effects. Changes of the amorphous phase and the appearance of crystalline phases were followed by Mossbauer spectroscopy and DSC measurements. The results indicate that contamination from the milling tools causes a shift of the chemical composition of the milled amorphous material. In the case of steel milling tools the appearance of bcc nuclei initiate crystallization during milling. Instead of this bcc structure, a modified amorphous phase with a broader hyperfine field distribution - attributed to the significant amount of dissolved tungsten-- is observed when the amorphous alloy is milled with tungsten carbide balls and vials.. The differences detected under experimental conditions where only the material of the vial was different confirm that the specific impurities introduced in the milling process play a decisive role in the crystallization of amorphous alloys under ball-milling conditions.