Composition- and temperature-dependent liquid structures in Al-Cu alloys: an ab initio molecular dynamics and x-ray...

Area of Science:

• Materials Science
• Physical Chemistry
• Computational Materials Science

Background:

• Understanding liquid alloy structures is crucial for materials processing.
• Aluminum-copper alloys are technologically important, but their liquid state behavior requires further investigation.

Purpose of the Study:

• To investigate the composition- and temperature-dependent liquid structures of Al-rich Cu binary alloys.
• To analyze the structural evolution and diffusion behavior during cooling.

Main Methods:

• High-temperature, high-energy X-ray diffraction (XRD) experiments.
• Ab initio molecular dynamics (AIMD) simulations.
• Analysis of local ordering using coordination number, bond-angle distribution, Honeycutt-Andersen index, bond-orientational order, and Voronoi tessellation.

Main Results:

• Excellent agreement between experimental XRD structure factors and AIMD simulations for liquid Al-rich Cu alloys.
• Continuous increase in heat capacity without abnormal peaks, differing from predictions for nanoliquids.
• Increasing deviation from Arrhenius behavior in Al and Cu diffusivities with higher Cu concentrations, linked to local ordering.

Conclusions:

• Cooling liquid Al-rich Cu alloys promotes Al2Cu crystal-like local atomic ordering, especially in hypereutectic compositions.
• Favorable short-range ordering between Cu and Al atoms is responsible for the observed non-Arrhenius diffusion behavior.