Nanoparticles (NPs) have high multifunctional potential to simultaneously enhance implant osseointegration and prevent infections caused by antibiotic-resistant bacteria. Here, we present the first report on using plasma electrolytic oxidation (PEO) to incorporate different combinations of reduced graphene oxide (rGO) and silver (Ag) NPs on additively manufactured geometrically ordered volume-porous titanium implants. The rGO nanosheets were mainly embedded parallel with the PEO surfaces. However, the formation of ‘nano-knife’ structures (particles embedded perpendicularly to the implant surfaces) was also found around the pores of the PEO layers. Enhanced in vitro antibacterial activity against methicillin-resistant Staphylococcus aureus was observed for the rGO+Ag-containing surfaces compared to the PEO surfaces prepared only with AgNPs. This was caused by a significant improvement in the generation of reactive oxygen species, higher levels of Ag⁺ release, and the presence of rGO ‘nano-knife’ structures. In addition, the implants developed in this study stimulated the metabolic activity and osteogenic differentiation of MC3T3-E1 preosteoblast cells compared to the PEO surfaces without nanoparticles. Therefore, the PEO titanium surfaces incorporating controlled levels of rGO+Ag nanoparticles have high clinical potential as multifunctional surfaces for 3D-printed orthopaedic implants.

The effect of ferrite-pearlite and ferrite-martensite phase combinations on the passive layer properties of low carbon steel is investigated in a 0.1 M NaOH solution. Heat treatments were designed to obtain ferrite-pearlite and ferrite-martensite microstructures with similar ferrite volume fractions. Potentiostatic polarisation and electrochemical impedance spectroscopy (EIS) results demonstrated the lower barrier properties of passive films on ferrite-martensite microstructure compared to the ones formed on ferrite-pearlite microstructure. This was attributed to the higher donor density of the passive layer on ferrite-martensite samples, measured with Mott–Schottky analysis. This behaviour was explained by the complex microstructure morphology of the martensite phase that led to the formation of a more defective passive film.

This work investigates the role of grain size and recrystallization texture in the corrosion behavior of pure iron in 0.1 M sulfuric acid solution. Annealing heat treatment was applied to obtain samples with different average grain sizes (26, 53 and 87 µm). Optical microscopy, X-ray diffraction and electron backscatter diffraction techniques were used to characterize the microstructure. The EBSD data analysis showed ferrite phase with no inclusions and very low geometrically necessary dislocation density, indicating strain-free grains constituting all samples. The crystallographic texture analysis of the samples revealed that the 26 µm grain size sample had a high volume fraction of {111} oriented grains parallel to the sample surface, while other samples exhibited nearly random crystallographic texture. The electrochemical results from potentiodynamic polarization and electrochemical impedance spectroscopy showed a decrease in corrosion resistance from 87 µm to 53 µm grain size sample and then an increase for the 26 µm grain size sample. This increase was attributed to the dominant effect of recrystallization texture on the corrosion behavior of the sample. The cathodic hydrogen evolution reaction kinetics was found to play a decisive role in the corrosion behavior of iron.

The role of prior austenite grain size (PAGS) on the passive layer properties of martensitic steels is studied. Electron backscatter diffraction analysis shows that PAGS between 5 and 66 µm were obtained after applying different heat treatments. The barrier properties of passive film deteriorate with grain refinement up to 28 µm, attributed to increased donor density and a decrease in the fraction of γ-Fe₂O₃ in passive films. However, the further refinement of PAGS to 5 µm leads to improvement in the barrier properties due to the changes within the martensite structure. This improvement stems from the increase in γ-Fe₂O₃ fraction.