Directing Surface Functions by Inducing Ordered and Irregular Morphologies at Single and Two-Tiered Length Scales

Surface topography outlines material's interaction with its immediate environment. Herein, a series of cost-effective and scalable treatments are used to obtain single-scale and two-tiered surfaces with ordered/disordered arrangements of micro and nano features. The applied treatments induced a wide variety of surface features regarding length scale and arrangement. The individual and synergistic contributions of roughness length scale, regularity, and hierarchy are analyzed on surface functionalities. The performance of further functionalized and lubricant-infused surfaces is evaluated regarding their interaction with wetting media, as well as tribological and electrochemical resistance. The hierarchical surfaces show improved wear and corrosion resistance. The prominence of the surface features’ length scale and orderedness varies based on the loading conditions and test environments. Wettability is mainly directed by micro-scale features. Tribology is largely led by the ability of the surfaces in forming a stable low-surface-energy liquid interface. Electrochemical activity is primarily influenced by the synergic barrier effect of the nano-features and the infused lubricant regardless of their arrangement. The results indicate that combining the distinctive and complementary role of micro and nano features can offer the possibility of obtaining versatile multifunctional surfaces with tunable performances based on the expected in-service conditions

Impact of shot peening on corrosion performance of AZ31 magnesium alloy coated by PEO: Comparison with conventional surface pre-treatments

This paper deals with the evaluation of the influence of selected pre-treatments, namely shot peening, polishing and grinding, used prior to plasma electrolytic oxidation (PEO) on the corrosion characteristics of AZ31 magnesium alloy in solution of 0.1 M NaCl. Additionally, selected combinations of pre-treatment and PEO coating were optimized in terms of the PEO preparation time. Corrosion characteristics of prepared surfaces were determined by the electrochemical impedance spectroscopy (EIS) during 168 h of exposure at the laboratory temperature followed by the equivalent circuit analysis of measured Nyquist diagrams. Localised corrosion events of selected combinations of pre-treatment and PEO coating were observed by local electrochemical impedance spectroscopy (LEIM) in 1 mM NaCl supplied by the potentiodynamic polarization tests. The obtained results showed that despite the negative impact of shot peening on the electrochemical reactivity of AZ31 alloy, this technique significantly enhanced corrosion stability of the subsequently formed PEO coating

Inclined and multi-directional surface impacts accelerate biodegradation and improve mechanical properties of pure iron

Impact based surface treatments with adequate kinetic energy have favorable effects on promoting cell-substrate interactions, reducing bacterial adhesion, and enhancing fatigue performance of metallic biomaterials. Here, we used both numerical and experimental approaches to evaluate the potential of these treatments for addressing the major issue associated with the application of pure iron in biomedical implants, i.e. its low corrosion rate. Despite the efficiency of impact based surface treatments in modulating the degradation rate of pure iron, the maximum reported depth of the affected surface layer is still limited, even when extreme process parameters are used. To address this issue, herein, two impact based treatments were adjusted to trigger the dislocation activities that facilitate grain refinement in pure iron using multi-directional inclined impacts. An alternative approach of severe shot peening (SSP) was developed and compared with ultrasonic shot peening (USP). The effect of both treatments and variations of their key parameters were analyzed considering the significant role of shear bands and dislocation cells in the grain refinement mechanism of pure α-iron. Microstructural, mechanical and electrochemical properties of the treated material were analyzed. The observations showed extension of the grain refined layers for the specimens subjected to multidirectional oblique impacts compared to the ones treated in the classic manner using normal impacts. The results imply that by adapting peening parameters, it would be possible to effectively create a thick surface layer with properties that can accelerate the biodegradation of pure iron boosting its potential to meet clinical requirements for temporary hard tissue implants

Effect of phosphating time on protection properties of hurealite coating: Differences between ground and shot peened HSLA steel surface

Shot peening is a standard surface treatment primarily used for enhancement of fatigue properties of metallic materials. However, its influence on surface properties is so radical, that subsequent techniques of surface treatment used on the shot peened surface need to be reconsidered in order to minimize the possible negative side effects of shot peening. In this case, the differences between hurealite formation on the ground and shot peened surfaces of modern high strength low alloy (HSLA) steel were evaluated by morphological and electrochemical corrosion observations and measurements. The surface morphologies of the formed coatings were observed by the scanning electron microscopy (SEM) and analysed by energy-dispersive X-ray analysis (EDX). The corrosion resistance of the HSLA steel with hurealite coating was evaluated using electrochemical impedance spectroscopy (EIS) by the analysis of Nyquist plots obtained in 0.1 M NaCl solution after various phosphating times on both types of pre-treated surfaces (ground and shot peened). The results showed that used technique of shot peening negatively influenced the phosphating process by prolonging the phosphating process in order to reach the coating with maximal protection properties in tested medium. Moreover, shot peened surface caused significantly enlarged size of the hurealite crystals and greater thickness of the coating compared to the surface pre-treated by grinding on the tested HSLA steel at the expense of a lower compactness and corrosion protection