Structure of polycrystalline Al-Ni-Fe-La alloys after quenching and plastic deformation by shear under pressure

The structure and phase composition of aluminum-based polycrystalline alloys (85 at % Al) containing transition (Fe, Ni) and rare-earth (La) metals are studied by metallography, differential scanning calorimetry, X-ray diffraction, and electron-microscopic analysis after melt quenching and subsequent severe plastic deformation (SPD) by shear under pressure. The melt-quenched alloys are shown to have a four-phase structure consisting of an aluminum-based solid solution, intermetallics Al₃Ni and Al₁₁La₃, and iron intermetallics. SPD results in the fragmentation and spheroidization of all phase constituents of the alloys and in the dissolution of the iron intermetallics. A multiphase nanostructured state forms in the alloys. The nanocrystallite sizes after SPD at various deformation parameters are determined. The microhardness is maximal after deformation corresponding to six anvil revolutions at a pressure of 8 or 10 GPa. The structural parameters and the microhardnesses are compared after SPD by shear under pressure of the alloys having the same compositions and different structural states (namely, amorphous and polycrystalline) before deformation. An amorphous-nanocrystalline structure with the minimum nanograin sizes and the maximum microhardnesses forms in the alloys having an initial amorphous structure and subjected to SPD.