Qin Jingyu

Structure factors of modified liquid Al–Si alloys

Abstract The structure factor and the coordination numbers of liquid Al–Si alloys with different Si content have been measured by a high temperature X-ray diffractometer. Radial distribution functions (RDFs), the nearest atomic distance and the coordination numbers of eutectic Al–Si alloys before and after being modified with Sr and Sb were studied. The RDFs of the liquid alloy were decomposed by five Gaussian peaks. The results show that a Si–Si covalent bond exists in the liquid of eutectic and hyper-eutectic alloys. Sr in the liquid Al–Si has a capability to weaken the covalent bonds of Si–Si, suppressing the nucleation of the eutectic silicon phase. On the other hand, Sb in the liquid Al–Si increases the order degree of Si atoms, decreasing the supercooling degree of the nucleation and promoting the nucleation of eutectic silicon.

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

The liquid structure of the 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 clearly exists up to a 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 the liquid Cu70Ni30 alloy mainly consist of Cu atoms with centred Ni atoms. The appearance of the pre-peak in the structure factor of the liquid Cu70Ni30 alloy is caused by the interaction between centred Ni atoms locating in the neighbouring atomic clusters.