Surface hardening of metals at room temperature by nanoparticle-laden cavitating waterjets

Reported in this paper is a novel and facile room-temperature surface-hardening technique, capable of providing five-fold increase in the hardness of an aluminum alloy, by utilizing a cavitating waterjet laden with hard nanoparticles. Microstructural and composition analyses reveal several mechanisms responsible for surface hardening: strain hardening, grain refinement, and dispersion strengthening. The hardened alloy surface also exhibits about 50% reduction in friction in a series of microscale friction measurements. Without the need to treat the alloy at elevated temperatures, this technique obviates such problems as additional energy usage, part distortion, microstructural and composition changes, and thermal shock-induced cracking. Equally important, this new method could be further tailored to impart metals, polymers, composites, etc. with different surface functional properties.