Femtosecond Laser Preparation of Terracotta Warrior-like Pit Superhydrophobic Structure on Magnesium Alloy with Mechanical Durability and Corrosion Resistance.

Abstract

Magnesium alloys are among the most promising materials for medical implants, and by preparing a superhydrophobic surface, the rate of corrosion can be effectively slowed down and durability be improved. However, the anticorrosion surfaces are inevitable to be damaged for the conventional micro-nanostructured superhydrophobic magnesium alloys, which highly limits their application prospects. This work proposes the development of a Terracotta Warrior pit superhydrophobic structure (TWPSS), consisting of a wall structure with a Terracotta Warrior-like pit and a lotus-like surface papillae structure within the wall. For the first time, top-down laser ablation of the pits to prepare the lotus-like surface papilla structure is used in conjunction with a bottom-up laser-guided melt stacking of the raised wall structure to achieve rapid fabrication of a TWPSS on a magnesium alloy surface. The Cassie-Baxter-based design of the wall structure spacing effectively protects the internal lotus-like surface papillae from damage and the disappearance of low surface energy material, and the results show that the superhydrophobic surfaces of magnesium alloys have excellent mechanical durability and repairability. In addition, it was found that the recast layer and laser melting stacked layers produced on the surface of the alloy during femtosecond laser processing refined the grain size of the magnesium alloy and effectively suppressed the corrosion rate. The combination of the superhydrophobic gas layer and the resulting grain refinement slowed down the corrosion of the magnesium alloy. Thus, the rapid preparation of TWPSS structures with mechanical durability and corrosion resistance by femtosecond lasers expands the clinical applications of superhydrophobic surface magnesium alloys in medical devices.