Amorphization of pure aluminium in ultraprecision cutting process: experimental observation and theoretical analysis

Preparing amorphous pure metals has long been significantly challenging because of their stringent transformation requirements. Here, we report a surprising discovery: the preparation of a layer of amorphous aluminium by ultraprecision cutting a polycrystalline bulk material. The findings indicated that under specific cutting conditions, polycrystalline aluminium was transformed into a completely amorphous phase on the surface layer. Additionally, the material matrix exhibited shear bands, including an amorphous phase, a 9 R phase, and high-density SFs. The modification resulted in a significant increase in surface micro-hardness, with the average value increasing from 0.93 ± 0.13 GPa to 2.21 ± 0.92 GPa. The amorphization in the ultraprecision cutting process is attributed to the high shear strain and strain rate, as confirmed by molecular dynamics simulation and theoretical calculation. This study provides a novel approach for preparing an amorphous layer on a crystalline aluminium bulk material to enhance its surface properties.