Structure and thermal stability of melt-quenched Al92−xNi8(Ce,Sm)x alloys with x=1, 2 and 4

The formation of metastable phases and their transformation behavior during constant-rate heating of melt-quenched Al92−xNi8REx (x=1, 2 and 4, numbers indicate at.%) alloys with the rare-earth (RE) elements Ce or Sm have been investigated by X-ray diffraction (XRD) and differential scanning calorimetry. According to the XRD results, for the Al–Ni–Sm system all the as-quenched alloys consist of a nanocrystalline phase with face-centered cubic (fcc) structure embedded in an amorphous phase. On the other hand, for the Al–Ni–Ce system only the as-quenched x=1 and x=2 alloys consist of a nanocrystalline phase with a fcc structure and a possible amorphous phase with very small volume fraction, whereas the x=4 alloy is amorphous. Upon heating, the partially crystalline alloys Al91Ni8Sm1, Al90Ni8Sm2, Al91Ni8Ce1 and Al90Ni8Ce2 show one broad exothermic peak of crystallization and the final phases are fcc Al solid solutions with a mixture of Al3Ni and Al3RE crystallization, all with nanosized grains. For the amorphous Al88Ni8Ce4 alloy and for the partially crystalline Al88Ni8Sm4 alloy, the crystallization occurs in three overlapping stages, the first one corresponding to the primary crystallization of the fcc-Al. The final microstructure of the latter two alloys is the same as that corresponding to the partially crystalline alloys.