Short-Range Order and Pair Interactions in Binary Nickel Alloys

Abstract

Diffuse wide-angle scattering from single crystals of binary alloys offers the opportunity of obtaining detailed quantitative information on the microstructure of the alloys, i.e. the pair correlation function and the static atomic displacements. A large scattering contrast, i.e. difference in the atomic scattering factors of the components, maximizes the contribution from short-range order and the linear static atomic displacements. An enhancement of this contrast may be achieved by employing synchrotron radiation along with X-rays from conventional sources or thermal neutrons. A critical item then consists in subtracting the inelastic or incoherent scattering and to separate the various elastic contributions. From the pair correlation function effective pair interactions may be deduced. Monte-Carlo simulations are used to estimate the stability of ordered phases in the coherent phase diagram, which may be compared with experimental findings. In the following, results from such experiments on the binary solid solutions Ni-8.9 at.% Al, Ni-11.2 at.% Mo and Ni-19:9 at.% Cr are summarized.