Mechanical alloying of brittle materials

Mechanical alloying by high energy ball milling has been observed in systems with nominally brittle components. The phases formed by mechanical alloying of brittle components include solid solutions (Si+Ge&rarrSiGe solid solution), intermetallic compounds (Mn+Bi&rarrMnBi), and amorphous alloys (NiZr2+Ni11Zr9&rarramorphous Ni50Zr50). A key feature of possible mechanisms is the temperature of the powders during milling. Experiments and a computer model of the kinetics of mechanical alloying were carried out in order to estimate the temperature effect. Temperature rises in typical powder alloys during milling in a SPEX mill were estimated to be &le350 K using the kinetic parameters determined from the computer model. The tempering response of fresh martensite in an Fe-1.2 wt pct C alloy during milling was consistent with the maximum result of the computer model, yielding temperatures in the powders of &le575 K (i.e., ΔT&le300 K). Thermal activation was required for mechanical alloying of Si and Ge powder. No alloying occurred when the milling vial was cooled by liquid nitrogen. The possible mechanisms responsible for material transfer during mechanical alloying of brittle components are considered.