Structural Change of Cr-N Powders during Mechanical Alloying Process

Abstract

Cr-N amorphous powders have been produced through the solid-gas reaction subjected to mechanical alloying(MA) of pure Cr powders under N₂ gas atomsphere and through the solid state reaction subjected to the MA of a mixture of Cr, Cr₂N and CrN powders under Ar gas atomsphere. The atomic structure during amorphization process was observed by X-ray and neutron diffraction. An advantage of the neutron diffraction technique allows us to observe the local structure surrounding a N atom because of a large coherent scattering length of the N atom in comparison with that of the Cr atom. The coordination number of metal atoms around a N atom approaches with 5-5.5 atoms. This implies that the nitrogen atom is located at both of centers of the tetrahedron, octahedron and/or trigonal prism formed by metal atoms to stabilize the amorphous structure.