Surface and Coatings Technology

  1. Publication date: 15 October 2019

    Source: Surface and Coatings Technology, Volume 375

    Author(s): G. Lazzini, L. Romoli, A.H.A. Lutey, F. Fuso

    Abstract

    The influence of surface topography resulting from ultrashort pulsed laser texturing on bacterial cell adhesion is studied as a method for preventing contamination on stainless steel components. The initial adhesion of a single spherical cell on a rough surface prior to the onset of any chemical or biological effect is simulated with a numerical approach including non-covalent interactions between the cell and textured substrate. The study demonstrates that when asperities are large enough to allow the cell to occupy valleys between two adjacent protrusions, the cell is protected from hydrodynamic turbulence and is therefore more prone to adhere to the substrate. Results pave the way to validating, in quantitative terms, hypotheses relating to the influence of surface topography on bacterial growth. Two different levels of anisotropy are taken into account to contrast the high adaptability of spherical cells, demonstrating that laser texturing can invoke a specific biological response.

  2. Publication date: 15 October 2019

    Source: Surface and Coatings Technology, Volume 375

    Author(s): M.J.R. Stegmueller, R.J. Grant, P. Schindele

    Abstract

    Friction surfacing offers a means of producing coatings between dissimilar materials through a solid state process; a union that would otherwise be classed as incompatible for liquid state coating processes. A method of using a rotating consumable friction rod supplemented by inductive heating was employed to produce conditions necessary for a sound bond between a stainless steel coating and an aluminium substrate. The rotational speed of and load on the coating rod influenced the bond strength significantly with low rotational speeds and high load values producing a good bond quality; however, cavitations at the coating-substrate interface showed a detrimental effect on the bond quality. Mechanical interlocking could be identified from images of longitudinal cross-sectional slices which were recorded using optical microscopy. An image recognition software tool was used to generate an interfacial roughness profile graph which described the coating-substrate interface. Additional filtering of the profile graph showed the depth of mechanical interlocking of the stainless steel coating into the aluminium substrate with the degree of this interlocking quantified by roughness values calculated from the profile graph. Large roughness values can be related to high coating push-off strengths (up to 107 MPa), and also were a result of low rotational speeds and high load values during friction surfacing. Dovetail shaped mechanical interlocks identified in the profile produced both high push-off and shear strength when compared with wedge-shaped interlocks; which, overall, provided good shear strengths up to 126 MPa.

  3. Publication date: 25 September 2019

    Source: Surface and Coatings Technology, Volume 374

    Author(s): Pyry-Mikko Hannula, Sven Pletincx, Dawid Janas, Kirsi Yliniemi, Annick Hubin, Mari Lundström

    Abstract

    The electrodeposition-redox replacement (EDRR) process was studied to control the creation of copper and silver containing particles on the surface of a carbon nanotube film. Synthetic solutions simulating typical hydrometallurgical copper electrolysis process solutions (40 g/L Cu, 120 g/L H2SO4) with different dilute concentrations of silver (1–10 ppm) were utilized as the source for particle deposition and recovery. Such process solutions are currently underutilized for use as a potential source for the deposition of noble particles. The effect of deposition voltage, deposition time, stirring, and redox replacement time between deposition pulses were investigated as the parameters affecting the morphology and composition of the deposited particles as well as deposition kinetics. The results showed that pure copper particles can be deposited when the redox replacement time between deposition pulses is very short (t = 2 s). By increasing the redox replacement time (t = 50 s and more) the original copper particle composition transforms into a core-shell structure with an outer layer predominately consisting of silver or a bimetallic mix of copper and silver, depending on the deposition conditions. The bimetallic Cu/Ag particle size could be controlled from 200 to 840 nm by the applied deposition voltage. At high redox replacement times (t = 150 s and more) the resulting particles were shown to be pure silver with a small diameter from 100 to 250 nm.