PRECIPITATION OF BCC NANOCRYSTALS IN BULK MG-CU-Y AMORPHOUS-ALLOYS

Coexistent amorphous and nanoscale bcc-Mg7Li3 phases were found in slo wly quenched alloys of the Mg65-xLixCu25Y10 system containing 3 to 15 at. % Li. The crystallization behavior of these alloys has been studie d, The grain size of the nanocrystalline bcc phase which is formed ran ges from 2 to 20 nm. The volume fraction of nanocrystalline phases as well as the grain size of the nanocrystals increase as the Li composit ion increases. Transmission electron microscopy studies suggest that t he alloy exhibits phase separation in the undercooled liquid state and that the nucleation and growth of the bcc-nanocrystals is related to the phase separation, Some characteristic thermal properties of the gl assy phase are presented, and the composition dependence of Tg and Tx is discussed. It is concluded that the addition of a small amount of L i is essential for the production of a bcc nanocrystalline phase in th e Mg-Li-Cu-Y system.