The microstructure evolution of aluminum implanted with nickel at 5 MeV and
at 100 K to a local concentration of 25 at. % is described. Transmission
Electron Microscopy (TEM) observa- tions and Rutherford Backscattering
Spectrometry (RBS) experiments are conducted to deter-mine the Ni profile
and the microstructure of the implanted samples. For lower Ni concentration,
it has been previously observed that Al0.75Ni0.25
amorphous precipitates are formed together with a high dislocation density.
When the Ni concentration reaches 25 at. %, a new crystalline multi-layered
microstructure is observed: the TEM observations reveal the presence of
well-defined crystalline layers separated by sharp interfaces. To our
knowledge, it is the first time that such a structure is observed without
further annealing of the implanted sample. A series of mechanisms describing
the formation of the crystalline multilayer are briefly discussed. It is
argued that its formation is the result of a recrystallization front
produced by the exothermal amorphous to crystal transformation.