EFFECT OF CU OR AG ON THE FORMATION OF COEXISTENT NANOSCALE AL PARTICLES IN AL-NI-M-CE (M=CU OR AG) AMORPHOUS-ALLOYS

The precipitation of a primary Al phase upon annealing of amorphous Al87Ni10Ce3, Al87Ni7Cu3Ce3 and Al87Ni8Ag2Ce3 alloys was found to occur only through a growth mechanism, based on the result that the exothermic reaction due to the precipitation of Al phase on the DSC curve does not have an incubation stage. The activation energy for the growth of the Al phase decreases from 1.82 eV for the Al-Ni-Ce alloy to 1.44 to 1.56 eV for the Al-Ni-M-Ce (M = Cu or Ag) alloys and the annealing temperature and time regions where the Al phase grows extend by the replacement of M for Ni. The particle size of the Al phase decreases from 9 nm for the ternary alloy to 3 to 5 nm for the quaternary alloys, accompanying the significant increase in the number of the Al particles. The extremely fine mixed structure consisting of nanoscale Al particles embedded in the amorphous matrix is formed in the Al-Ni-M-Ce alloys containing Cu or Ag elements which are soluble to the Al phase. The formation of the mixed structure is presumably due to the combination of (1) the necessity of the redistribution of the M elements for the growth of the Al particles resulting from the difference between the soluble content of the M elements into the Al particles and the nominal M content in the amorphous matrix, and (2) the increase in the number of the pre-existing nuclei of Al-rich zone resulting from the increase in the apparent Al content caused by the replacement of Ni by the M elements. The finding of the M elements leading to the refinement of the nanoscale Al particles is important in the subsequent development of the nanoscale mixed phase alloys.