Structural characterization by ~(27)Al solid-state NMR and neutron powder diffraction of intermetallic alloys in the Al-Si-Ni system

摘要

Al-Si-Ni ternary intermetallic alloys belonging to the orthorhombic #delta#-Ni_2Si structural type have been investigated by X-ray, neutron powder diffraction and solid-state ~(27)Al-NMR. Structural analysis shows that all the #delta#-Ni_2Si type alloys are genuine solid solutions. NMR spectroscopy has shown that in all the investigated samples. Al exhibits a strong metallic character. At constant Ni concentration (66.67), only one NMR peak corresponding to #delta#-Ni_2Si is observed, whereas for lower Ni contents, two peaks corresponding to #delta#-Ni_2Si+NiAl are observed. The variations of the chemical shifts of these peaks versus Al concentration are discussed in terms of unit-cell volumes, phase compositions and free energy.