A strong, wear- and corrosion-resistant, and antibacterial Co–30 at.% Cr–5 at.% Ag ternary alloy for medical implants

A Co–30 at.% Cr–5 at.% Ag alloy was fabricated using a combination of mechanical alloying and spark plasma sintering. The microstructure of the alloy consisted of an ultrafine-grained ε-Co solid solution matrix with an average grain size of 167 nm and uniformly dispersed Ag particles with an average size of 72 nm and a minor amount of nanoscale σ-precipitates with size of 23 nm. Such particular microstructure enabled high hardness of 650 HV and compressive strength of up to 2.3 GPa. Pin-on-disk dry sliding wear tests show that the present alloy exhibited superior wear resistance, with wear rate in the order of 10 mm/(N·m) upon sliding against alumina. The wear-induced microstructure extended only ~500 nm from the sliding surface, with elongated Ag particles. The alloy also demonstrated high resistance to corrosion in artificial saliva solution, due to the formation of a protective passive film. Moreover, the addition of Ag also significantly enhanced the antibacterial activity of Co–Cr alloys, with antibacterial rates against E. coli and S. aureus of 90.5% and 72.6%, respectively. The present alloy with a combination of high strength, superior wear- and corrosion-resistance, and excellent antibacterial activity offers a promising candidate for medical implants.