Effects of La content on the glass transition and crystallization process of Al-Ni-La amorphous alloys

Effects of La content on the glass transition and crystallization process of Al94-xNi6Lax(x = 3-9) amorphous alloys were investigated by X-ray diffraction and differential scanning calorimeter. The results show that the thermal stability increases with increasing the La content. The crystallization changes from a two-stage process without glass transition at x = 3-6 to a three-stage one with obvious glass transition at x = 7-9. The first crystallization process results in precipitation of single fcc-Al at x = 3-5, fcc-Al plus metastable phase(s) at x = 6 and 7, and single metastable phase at x = 8 and 9. The first crystallization process at x = 4 and 5 is the growth of quenched-in nuclei, whereas that at x = 6, 7 and 9 is the diffusion-controlled growth with a decreasing, constant and increasing nucleation rate, respectively. The activation energy for the first crystallization process is larger in the eutectic reaction than that in the primary reaction, and is the highest when the number of the products is the most. (C) 2007 Elsevier Ltd. All rights reserved.