High energy ball milling of Co89B11 powders

Mechanical alloying was performed on elemental cobalt and baron powders wit h atomic ratio Co89B11. X-ray diffraction analysis (XRD) and differential s canning calorimetry were used to characterize the structure of the milled s amples before and after the heating. The high-energy ball milling was found to influence the resulting phases. The starting powder consisted of the tw o modifications of cobalt: hcp (hexagonal close packed) and fee (face cente red cubic). Depending on the milling time, single hcp, single fee, amorphou s phases or their mixture were formed. After milling for 20 h, one can obse rve that the fcc phase transforms into hcp. Further milling caused the amor phization of the alloy. The fee phase formed from the amorphous matrix only after 80 h of milling and then transformed partially into the hexagonal ph ase after further milling. The average crystallite size in the final sample obtained after 150 h of ball milling was about 6 nm. (C) 1999 Acta Metallu rgica Inc.