Diffuse scattering in disordered ternary alloys: neutron measurements of local order in a stainless steel Fe₀.₅₆Cr₀.₂₁Ni₀.₂₃

The local atomic arrangement in the stainless-steel alloy Fe_0.56Cr_0.21Ni_0.23 has been investigated by thermal neutron diffuse scattering from single crystals. The variation of contrast has been obtained by isotopic substitution: three single crystals of different isotopic compositions have been used. The Warren-Cowley parameters of the three heterogeneous pairs have been determined. It is shown that ordering occurs between Ni and Cr atoms. The correlation lengths are small and are of about one cell length. The static displacements are shown to be small. Analysis procedures of diffuse scattering from ternary alloys are developed from neutron scattering and in the Appendix for X-ray scattering.