Enhancing the bio-corrosion resistance of Ni-free ZrCuFeAl bulk metallic glass through nitrogen plasma immersion ion implantation

Improving the resistance of bulk metallic glass (BMG) to corrosion, particularly pitting, is crucial to the further development of this material. This study employed surface treatment based on nitrogen plasma immersion ion implantation (N-PIII) to enhance the bio-corrosion resistance of Ni-free Zr_62.5Cu_22.5Fe₅Al₁₀ BMG for application in bone implants. Resistance to bio-corrosion was evaluated by establishing potentiodynamic polarization curves in artificial saliva (AS) and simulated body fluid (SBF). Commercial pure Ti was used as the control. Results demonstrate that N-PIII treatment did not alter the bulk amorphous structure of Zr_62.5Cu_22.5Fe₅Al₁₀ BMG. Following N-PIII treatment, a nitride-containing 15 nm thick oxide film was formed on the BMG. This film significantly improved resistance to bio-corrosion in both AS and SBF solutions. The N-PIII-treated BMG presented lower corrosion rates (50-67% less) and higher corrosion potential (800-1100 mV more) than that observed in untreated BMG and Ti. The N-PIII treatment also significantly improved resistance of the BMG to pitting (increased pitting potential by 500-700 mV). This is the first report of the outstanding resistance of Ni-free Zr-based BMG to bio-corrosion (i.e. corrosion rate 0.01 μA/cm²; pitting potential >1200 mV; corrosion potential >270 mV) in simulated biological environments.