Biodegradation behaviour of Fe-based alloys in Hanks’Balanced Salt Solutions:Part I.material characterisation and corrosion testing

Research on Fe-based biodegradable alloys for implant applications has increased considerably over the past decade.However,there is limited information on the influence of testing electrolytes on corrosion product formation and general corrosion progress.In this work,the effect of Hanks’Balanced Salt Solution(HBSS)with or without Ca^(2+)on the corrosion of Fe,Fe35Mn and(Fe35Mn)5Ag powder-processed coupons has been studied using potentiodynamic polarisation,Electrochemical Impedance Spectroscopy(EIS),and preliminary localised measurement of pH and dissolved oxygen concentration in close proximity to the metal surface.Both Fe35Mn and(Fe35Mn)5Ag alloys showed accelerated corrosion when compared to pure Fe based on potentiodynamic testing results,with FeMnAg exhibiting the highest corrosion rate in Ca^(2+)-containing HBSS.The results indicate that in Ca^(2+)-containing HBSS,the formation of a partially protective Ca/P layer decelerates the corrosion progress,whereas the Fe-and Mn-phosphates formed in Ca^(2+)-free HBSS do not have the same effect.The Ca/P layer on(Fe35Mn)5Ag experienced a reduction in resistance following several hours of testing,indicating partial loss of its protective effect.

Biodegradation behaviour of Fe-based alloys in Hanks’Balanced Salt Solutions:Part II.The evolution of local pH and dissolved oxygen concentration at metal interface

Commercially pure Fe,Fe35Mn,and(Fe35Mn)5Ag alloys were prepared by uniaxial pressing of the mixture of individual powders,followed by sintering.The influence of the alloying elements Mn and Ag on the corrosion behaviour of these Fe-based alloys was investigated in Hanks’Balanced Salt Solution(HBSS).Furthermore,the role of the components in HBSS,particularly Ca^(2+)ions during alloys degradation was studied.Distribution of local pH and dissolved oxygen concentration was measured 50μm above the interface of the degrading alloys.The results revealed that 5 wt%Ag addition to Fe35Mn alloy triggered micro-galvanic corrosion,while uniform corrosion dominated in pure Fe and Fe35Mn.Fast precipitation of Ca-P-containing products on the surface of these Fe-based alloys buffered local pH at the metal interface,and blocked oxygen diffusion at the initial stages of immersion.In the(Fe35Mn)5Ag,the detachment or structural changes of Ca-P-containing products gradually diminished their barrier property.These findings provided valuable insights into the degradation mechanism of promising biodegradable Fe-based alloys.