COPPER-ALLOYS AND COBALT-ALLOYS MADE BY MECHANICAL ALLOYING

Mechanical alloying has been achieved by ball milling in horizontal and attritor mills in elemental powder mixtures of the following binary metallic systems: Co-Cu, Co-Ti, Co-Sn, Cu-Al, Cu-Fe, Cu-Zn and Co-Sn. These binary systems represent a variety of conditions regarding crystal structures of the elements and types of equilibrium phase diagrams. With the exception of the Co-Ti system, in which an amorphous phase predominated after long milling times, mechanical alloying lead to the formation of the same phases found in the respective equilibrium phase diagrams, albeit with differences in the phase compositions. It was observed that some of the possible phases were preferentially formed at the expense of others; as a consequence, their compositional ranges of existence were extended and shifted over those established under equilibrium conditions. It is argued that thermodynamic considerations represent the main issue involved in the occurrence of phase selection during mechanical alloying.