A Ni- and Cu-free Zr-based bulk metallic glass with excellent resistance to stress corrosion cracking in simulated body fluids

In order to evaluate stress corrosion cracking (SCC) susceptibility of a Ni- and Cu-free Zr ₅₆Al ₁₆Co ₂₈ bulk metallic glass (BMG) for biomedical application, the SCC behaviour of the BMG in various simulated body fluids (SBFs) including Hanks', PBS(-) and 0.9% NaCl solutions open to air at 37°C has been investigated using a slow strain rate technique (SSRT) at various initial tensile strain rates in the region of 5×10 ^-7 to 5×10 ^-4s ^-1. It was found that the Zr-Al-Co BMG exhibited excellent resistance to SCC in all of tested conditions. The amounts of cytotoxic cobalt ions released from the BMG disks of 5mm in diameter were lower than those from the currently used biomaterial Co-Cr-Mo alloy. XPS analysis revealed that zirconium and aluminium ions were enriched in both air-formed and passive films. Moreover, these films were composed of double oxyhydroxide of zirconium, aluminium and cobalt. The formation of the stable and homogeneous double oxyhydroxide film enriched with zirconium and aluminium cations seems to be responsible for the high corrosion resistance and hence good SCC resistance of the Zr-Al-Co glassy alloy in SBFs. Thus, the Zr ₅₆Al ₁₆Co ₂₈ BMG can be potentially promising material for biomedical applications.