THE ICOSAHEDRAL TO CRYSTALLINE TRANSFORMATION IN AL51CU12.5LI16.5MG20MELT-SPUN RIBBONS

The results of experiments on the icosahedral to crystalline transform ation of melt-spun Al51Cu12.5Li16.5Mg20 are reported. The microstructu ral characteristics of the alloy, in all stages of the transformation, have been determined using a combination of transmission electron mic roscopy, X-ray diffraction and differential scanning calorimetry. The as-spun alloy consists of icosahedral grains with a low volume fractio n of quenched-in crystallites. The quasilattice constant is calculated to be 0.505 nm. Upon annealing at 394-degrees-C for 20 min, the icosa hedral phase completely transforms to Al5Cu(Li, Mg)3 (a b c c phase), aluminium and a hexagonal phase. The orientation relationships and che mical compositions of all phases involved are established. Electron mi croscopy reveals planar defects in all the crystalline phases (except aluminium). The planar defects in the b c c phase are on {110} and {10 0}-type planes. Defects in the hexagonal phase are found to be on {000 1} and {1120}-type planes.