Short-Range and Medium-Range Order in Liquid Cu-Ni Alloy

The liquid structure of Cu₇₀Ni₃₀ alloy has been investigated using a θ - θ high-temperature x-ray diffractometer. At all temperatures above its liquidus, a distinct pre-peak has been found around a scattering vector magnitude of 13.5nm^-1. The height of the pre-peak decreases gradually with increasing temperature but it is clearly existent up to temperature of 1400°C. This behaviour indicates that stable medium-range order atomic clusters exist in the melt. It is concluded that the short-range order atomic clusters of liquid Cu₇₀Ni₃₀ alloy mainly consist of Cu atoms with centered Ni atoms. The appearance of the pre-peak in the structure factor of liquid Cu₇₀Ni₃₀ alloy is caused by the interaction between centered Ni atoms locating in the neighbouring atomic clusters.