Ultrasound‐Assisted Liquid‐Phase Synthesis and Mechanical Properties of Aluminum Matrix Nanocomposites Incorporating Boride Nanocrystals

Abstract

Incorporating boride nanocrystals could significantly impact the mechanical properties of aluminum alloys. Molten salts synthesis offers opportunities to fabricate superhard boride nanoparticles, which can sustain the harsh conditions of liquid metallurgy synthesis, thus enabling liquid-phase design of metallic nanocomposites. Here we unveil HfB 2 -Al nanocomposites with molten salt-derived HfB 2 nanoparticles incorporated by ultrasound-assisted casting. Using sequential dilutions, the nanoparticles were incorporated in Al with macroscale homogeneity. The crystal structure and size of the nanocrystals is retained in the final nanocomposites, supporting their excellent chemical stability. Semi-coherent interfaces between the nanoparticles and the matrix are then evidenced by transmission electron microscopy, thus suggesting that the nanocrystals could act as nuclei for the solidification of Al and then limit the Al grain size to< ca. 20 µm. Nanoindentation measurements revealed significant grain boundaries strengthening effect. We finally show that HfB 2 nanoparticles also enable a strong decrease in matrix grain size and an increase in the hardness of the AlSi 7 Cu 0.5 Mg 0.3 cast alloy. This proof-of-concept material is paving the way to new light-weight Al matrix nanocomposites doped by molten-salt synthesized nanoparticles.