QUASI-CRYSTAL FORMATION AND PHASE-TRANSITIONS BY BALL MILLING

Quasicrystalline Al-Cu-Mn powder has been prepared by mechanical alloying. The quasicrystalline phase forms directly by milling via a solid-state reaction from the crystalline elemental powders. Single-phase quasicrystalline material is obtained for (15-25) at.% Cu and (10-20) at.% Mn. Besides, two-phase regions of quasicrystalline phase and crystalline material exist. The results are compared with data for melt-spun material. The milling conditions strongly affect the phase formation. For low milling intensity an amorphous phase instead of quasicrystalline material forms. High-intensity milling results in the formation of crystalline powder. The various phases can be transformed into each other by additional milling at higher or lower milling intensity. Possible mechanisms are proposed.