Thermal History-Dependent Coalescence Mechanisms and Sintering Dynamics in Al-6.8%Cu Nanopowders

TL;DR

This study uses molecular dynamics simulations to reveal how cooling rates and temperature influence coalescence mechanisms and microstructure evolution in Al-6.8%Cu nanopowders during sintering, impacting defect control and material strength.

Contribution

It uncovers the atomic-scale effects of thermal history on sintering mechanisms and microstructure formation in Al-Cu nanopowders, highlighting the importance of cooling rates.

Findings

Cooling rate significantly affects final microstructure.

High cooling rates can induce amorphous phases at interfaces.

Different coalescence mechanisms dominate at low and high temperatures.

Abstract

Aluminum-Copper (Al-Cu) alloys are essential materials for weight reduction critical structures in the aerospace and automotive industries, yet achieving their maximum ultrahigh-strength potential remains limited by nanoscale defect control during powder metallurgy processing. We employ large-scale molecular dynamics simulations on Al-6.8%Cu nanoparticles to explore atomic-scale mechanisms governing the full thermal sintering cycle. We demonstrate that while the sintering temperature primarily initiates neck formation, the subsequent cooling rate is the dominant kinetic parameter dictating the final microstructure. Fast cooling rates trap a significantly higher density of stacking faults and can unexpectedly lead to the formation of an amorphous phase at the interparticle interfaces, a feature critically dependent on the rate of thermal dissipation. We confirm a clear shift in the coalescence mechanism from plastic deformation (dislocation slip) at low temperatures (300 K and 450 K) to mass transport via atomic diffusion at high temperatures (600 K). These findings provide essential, atomic-scale guidelines for controlling thermal processing, particularly cooling rates, to design defect-stabilized, high-performance Al-Cu components.