Interdiffusion in liquid Al-Cu and Ni-Cu alloys

Area of Science:

• Materials Science
• Computational Materials Science
• Physical Chemistry

Background:

• Understanding interdiffusion is crucial for predicting alloy behavior during solidification.
• Liquid alloys like Al-Cu and Ni-Cu are technologically important, but their diffusion mechanisms require detailed study.

Purpose of the Study:

• To investigate interdiffusion processes in liquid Al-Cu and Ni-Cu alloys using molecular dynamics.
• To compare the predictive accuracy of the Darken relation against Maxwell-Stefan diffusivities.
• To calculate Fickian interdiffusivities and assess their dependence on alloy composition and undercooling.

Main Methods:

• Molecular dynamics simulations were employed to model liquid Al-Cu and Ni-Cu systems.
• Maxwell-Stefan diffusivities were computed using both the Green-Kubo method and the Darken relation.
• Fickian interdiffusivities were derived from calculated Maxwell-Stefan diffusivities and alloy activities.

Main Results:

• The Darken relation accurately predicts Maxwell-Stefan diffusivity for Ni-Cu alloys but overestimates it for Al-Cu alloys, particularly at medium concentrations.
• Fickian interdiffusivities exhibit strong composition dependence in both alloy systems.
• Estimates of Fickian interdiffusivities under varying undercooling conditions were obtained for specific Al-Cu and Ni-Cu compositions.

Conclusions:

• The study highlights the limitations of the Darken relation for certain alloy systems.
• The calculated interdiffusivities provide valuable data for refining solidification models.
• The findings contribute to improved quantitative predictions of dendrite growth velocity in alloys.