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

Magnesiumalloys are among the most promising materials for medicalimplants, and by preparing a superhydrophobic surface, the rate ofcorrosion can be effectively slowed down and durability be improved.However, the anticorrosion surfaces are inevitable to be damaged forthe conventional micro-nanostructured superhydrophobic magnesiumalloys, which highly limits their application prospects. This workproposes the development of a Terracotta Warrior pit superhydrophobicstructure (TWPSS), consisting of a wall structure with a TerracottaWarrior-like pit and a lotus-like surface papillae structure withinthe wall. For the first time, top-down laser ablation of the pitsto prepare the lotus-like surface papilla structure is used in conjunctionwith a bottom-up laser-guided melt stacking of the raised wall structureto achieve rapid fabrication of a TWPSS on a magnesium alloy surface.The Cassie-Baxter-based design of the wall structure spacingeffectively protects the internal lotus-like surface papillae fromdamage and the disappearance of low surface energy material, and theresults show that the superhydrophobic surfaces of magnesium alloyshave excellent mechanical durability and repairability. In addition,it was found that the recast layer and laser melting stacked layersproduced on the surface of the alloy during femtosecond laser processingrefined the grain size of the magnesium alloy and effectively suppressedthe corrosion rate. The combination of the superhydrophobic gas layerand the resulting grain refinement slowed down the corrosion of themagnesium alloy. Thus, the rapid preparation of TWPSS structures withmechanical durability and corrosion resistance by femtosecond lasersexpands the clinical applications of superhydrophobic surface magnesiumalloys in medical devices.