The effect of interpass temperature on the microstructure and pit nucleation behaviour in wire an... more The effect of interpass temperature on the microstructure and pit nucleation behaviour in wire and arc additive manufacturing (WAAM) deposited ER316L stainless steel was investigated. Lowering the interpass temperature increased the ferrite content and decreased the sigma phase precipitation. Potentiostatic pulse measurements showed that the WAAM ER316L pits developed predominantly near sigma phases and had higher pit density compared to a wrought 316L (UNS S31600). The pitting susceptibility of WAAM ER316L increases with increasing interpass temperature due to the precipitation of larger sigma phase enhancing the elemental segregation.
Marine biofilms can increase ship-related drag which has significant environmental and economic c... more Marine biofilms can increase ship-related drag which has significant environmental and economic consequences. Using Optical Coherence Tomography and rheometry we concluded that surface treatment influences biofilm structure and viscoelasticity which could implicate drag.
Corrosion performance of a multi-layered ER316LSi wall deposited using wire and arc additive manu... more Corrosion performance of a multi-layered ER316LSi wall deposited using wire and arc additive manufacturing was studied in the as-deposited condition and after stress relief heat treatment at 900 ℃, in 3.5 wt.% NaCl solution. It was found that the heat treatment is not suitable for WAAM ER316LSi components due to the complete transformation of the delta ferrite into sigma decreasing the corrosion performance. The delta ferrite to sigma transformation during heat treatment was facilitated by the cyclic reheating of the part during deposition. The electrochemical response of as-deposited WAAM differed from a wrought alloy with similar composition and linked to microstructural differences: as-deposited WAAM had a higher pitting potential due to the absence of sulfide inclusions and increased metastable activity due to the presence of the secondary delta ferrite causing elemental segregation.
In this study a miniaturised benchtop rotating disc method is described that uses test discs 25 m... more In this study a miniaturised benchtop rotating disc method is described that uses test discs 25 mm in diameter. A highly sensitive analytical rheometer is used to measure the torque acting on the discs rotating in water. Model rough surfaces were prepared by attaching different grades of sandpaper to the disc surface. Discs with experimental antifouling coatings applied were exposed in the marine environment for the accumulation of microbial fouling, and the rotor was capable of detecting the increased drag due to biofilm formation. The drag due to biofilm was related to an equivalent sand roughness height.
Tribocorrosion of Passive Metals and Coatings, 2011
Abstract: This chapter reviews research associated with the development of coatings that are desi... more Abstract: This chapter reviews research associated with the development of coatings that are designed to withstand combined wear and corrosion conditions. Better understanding of the performance of tribological coatings under these tribocorrosion conditions is crucial for the accurate prediction of equipment/component service life. The tribocorrosion performance of coatings deposited by a variety of techniques is discussed and the main mechanisms associated with their degradation under combined wear and corrosion highlighted. Coating composition, microstructure, defect level, adhesion, cohesion and substrate properties are often viewed as the most critical elements in coating performance when exposed to tribocorrosion contacts. The importance of post-coating deposition treatments such as laser resurfacing and sealing are also discussed. Interactions between wear and corrosion mechanisms are identified along with some models and mapping techniques that aim to inform coating selection and predict performance. Recent investigations into mono-layer, as well as multi-layered and functionally graded coatings, are reviewed as candidates for wear–corrosion-resistant surfaces. The review reveals the need for a more considered approach to tribocorrosion testing and the way in which the results are analysed and presented.
<p>The physical structure and mechanical properties of a biofilm ar... more <p>The physical structure and mechanical properties of a biofilm are known to respond to external stressors, such as hydrodynamic shear, and are expected to play a vital role in determining biofilm-associated drag. Yet, both, how these structural and mechanical properties interact with one another and with fluid flow, and how these interactions influence drag is poorly understood. In part this is due to a lack of standard methods for studying biofilm physical and mechanical (physico-mechanical) properties and relating them to drag. To date, rigid structures, such as sandpaper, have been typically used to model biofilms. Whilst rigid structures can simulate roughness, they neglect features such as viscoelasticity and heterogeneity. To address this, our novel work demonstrates the practical application of new test methods for biofilm research: the use of elastomeric and gel-like materials to better model biofilm physico-mechanics under controlled flow conditions, and the use of tensile and rheological testing to measure the elastic modulus of marine biofilms. Artificial biofilms were cast / made from materials with mechanical properties comparable to natural biofilms. Marine biofilms were grown in-house, within a recirculating system, using a field-sourced, mixed species inoculate. The elastic modulus of marine and artificial biofilms was measured using tensile and rheological testing.  Though elastic modulus has been recorded for biofilms previously, until now, the elastic modulus of marine biofilms had not been recorded; partly due to the complexity of their physical structures and their biological composition (bacterial and microalgal components). Despite biological differences, the elastic modulus of marine biofilms tested sits comfortably within the range recorded for other biofilms studied, at 0.0000098 MPa - 0.0002 MPa. A marine biofilm flow cell was utilised for pressure drop experiments, alongside the use of a non-invasive imaging technique, Optical Coherence Tomography. This experimental set-up enabled real-time visualisation and data collection of the physical response of the elastomers and biofilms grown in the marine environment to different flow rates. We found that for artificial biofilms, elasticity had a greater impact on biofilm-associated drag than roughness (P < 0.05). Biofilms are a unique and complex material, and therefore to better understand their physico-mechanical properties in flow, we first need to understand these properties independent of their complex biology. The use of fully artificial biofilms, with controlled properties, based on mechanical properties of marine biofilms, can help achieve this.</p>
International journal of molecular sciences, Jan 10, 2018
The use of natural products (NPs) as possible alternative biocidal compounds for use in antifouli... more The use of natural products (NPs) as possible alternative biocidal compounds for use in antifouling coatings has been the focus of research over the past decades. Despite the importance of this field, the efficacy of a given NP against biofilm (mainly bacteria and diatoms) formation is tested with the NP being in solution, while almost no studies test the effect of an NP once incorporated into a coating system. The development of a novel bioassay to assess the activity of NP-containing and biocide-containing coatings against marine biofilm formation has been achieved using a high-throughput microplate reader and highly sensitive confocal laser scanning microscopy (CLSM), as well as nucleic acid staining. Juglone, an isolated NP that has previously shown efficacy against bacterial attachment, was incorporated into a simple coating matrix. Biofilm formation over 48 h was assessed and compared against coatings containing the NP and the commonly used booster biocide, cuprous oxide. Leac...
ABSTRACT Dstl and EPSRC have jointly funded a 3-year project at the University of Southampton to ... more ABSTRACT Dstl and EPSRC have jointly funded a 3-year project at the University of Southampton to develop corrosion detection and monitoring systems for land, marine and aerospace structures. By combining microfluidics with new, emerging sensor technologies, this project aims to develop in-situ systems that not only detect the onset of structural corrosion, but can also assess its state and apply appropriate remediation to inhibit its progress.
The search for new antifouling (AF) coatings that are environmentally benign has led to renewed i... more The search for new antifouling (AF) coatings that are environmentally benign has led to renewed interest in the ways that micro-organisms colonize substrates in the marine environment. This review covers recently published research on the global species composition and dynamics of marine biofilms, consisting mainly of bacteria and diatoms found on man-made surfaces including AF coatings. Marine biofilms directly interact with larger organisms (macrofoulers) during colonization processes; hence, recent literature on understanding the basis of the biofilm/macrofouling interactions is essential and will also be reviewed here. Overall, differences have been identified in species composition between biofilm and planktonic forms for both diatoms and bacteria at various exposure sites. In most studies, the underlying biofilm was found to induce larval and spore settlement of macrofoulers; however, issues such as reproducibility, differences in exposure sites and biofilm composition (natural multispecies vs. monospecific species) may influence the outcomes.
The effect of interpass temperature on the microstructure and pit nucleation behaviour in wire an... more The effect of interpass temperature on the microstructure and pit nucleation behaviour in wire and arc additive manufacturing (WAAM) deposited ER316L stainless steel was investigated. Lowering the interpass temperature increased the ferrite content and decreased the sigma phase precipitation. Potentiostatic pulse measurements showed that the WAAM ER316L pits developed predominantly near sigma phases and had higher pit density compared to a wrought 316L (UNS S31600). The pitting susceptibility of WAAM ER316L increases with increasing interpass temperature due to the precipitation of larger sigma phase enhancing the elemental segregation.
Marine biofilms can increase ship-related drag which has significant environmental and economic c... more Marine biofilms can increase ship-related drag which has significant environmental and economic consequences. Using Optical Coherence Tomography and rheometry we concluded that surface treatment influences biofilm structure and viscoelasticity which could implicate drag.
Corrosion performance of a multi-layered ER316LSi wall deposited using wire and arc additive manu... more Corrosion performance of a multi-layered ER316LSi wall deposited using wire and arc additive manufacturing was studied in the as-deposited condition and after stress relief heat treatment at 900 ℃, in 3.5 wt.% NaCl solution. It was found that the heat treatment is not suitable for WAAM ER316LSi components due to the complete transformation of the delta ferrite into sigma decreasing the corrosion performance. The delta ferrite to sigma transformation during heat treatment was facilitated by the cyclic reheating of the part during deposition. The electrochemical response of as-deposited WAAM differed from a wrought alloy with similar composition and linked to microstructural differences: as-deposited WAAM had a higher pitting potential due to the absence of sulfide inclusions and increased metastable activity due to the presence of the secondary delta ferrite causing elemental segregation.
In this study a miniaturised benchtop rotating disc method is described that uses test discs 25 m... more In this study a miniaturised benchtop rotating disc method is described that uses test discs 25 mm in diameter. A highly sensitive analytical rheometer is used to measure the torque acting on the discs rotating in water. Model rough surfaces were prepared by attaching different grades of sandpaper to the disc surface. Discs with experimental antifouling coatings applied were exposed in the marine environment for the accumulation of microbial fouling, and the rotor was capable of detecting the increased drag due to biofilm formation. The drag due to biofilm was related to an equivalent sand roughness height.
Tribocorrosion of Passive Metals and Coatings, 2011
Abstract: This chapter reviews research associated with the development of coatings that are desi... more Abstract: This chapter reviews research associated with the development of coatings that are designed to withstand combined wear and corrosion conditions. Better understanding of the performance of tribological coatings under these tribocorrosion conditions is crucial for the accurate prediction of equipment/component service life. The tribocorrosion performance of coatings deposited by a variety of techniques is discussed and the main mechanisms associated with their degradation under combined wear and corrosion highlighted. Coating composition, microstructure, defect level, adhesion, cohesion and substrate properties are often viewed as the most critical elements in coating performance when exposed to tribocorrosion contacts. The importance of post-coating deposition treatments such as laser resurfacing and sealing are also discussed. Interactions between wear and corrosion mechanisms are identified along with some models and mapping techniques that aim to inform coating selection and predict performance. Recent investigations into mono-layer, as well as multi-layered and functionally graded coatings, are reviewed as candidates for wear–corrosion-resistant surfaces. The review reveals the need for a more considered approach to tribocorrosion testing and the way in which the results are analysed and presented.
<p>The physical structure and mechanical properties of a biofilm ar... more <p>The physical structure and mechanical properties of a biofilm are known to respond to external stressors, such as hydrodynamic shear, and are expected to play a vital role in determining biofilm-associated drag. Yet, both, how these structural and mechanical properties interact with one another and with fluid flow, and how these interactions influence drag is poorly understood. In part this is due to a lack of standard methods for studying biofilm physical and mechanical (physico-mechanical) properties and relating them to drag. To date, rigid structures, such as sandpaper, have been typically used to model biofilms. Whilst rigid structures can simulate roughness, they neglect features such as viscoelasticity and heterogeneity. To address this, our novel work demonstrates the practical application of new test methods for biofilm research: the use of elastomeric and gel-like materials to better model biofilm physico-mechanics under controlled flow conditions, and the use of tensile and rheological testing to measure the elastic modulus of marine biofilms. Artificial biofilms were cast / made from materials with mechanical properties comparable to natural biofilms. Marine biofilms were grown in-house, within a recirculating system, using a field-sourced, mixed species inoculate. The elastic modulus of marine and artificial biofilms was measured using tensile and rheological testing.  Though elastic modulus has been recorded for biofilms previously, until now, the elastic modulus of marine biofilms had not been recorded; partly due to the complexity of their physical structures and their biological composition (bacterial and microalgal components). Despite biological differences, the elastic modulus of marine biofilms tested sits comfortably within the range recorded for other biofilms studied, at 0.0000098 MPa - 0.0002 MPa. A marine biofilm flow cell was utilised for pressure drop experiments, alongside the use of a non-invasive imaging technique, Optical Coherence Tomography. This experimental set-up enabled real-time visualisation and data collection of the physical response of the elastomers and biofilms grown in the marine environment to different flow rates. We found that for artificial biofilms, elasticity had a greater impact on biofilm-associated drag than roughness (P < 0.05). Biofilms are a unique and complex material, and therefore to better understand their physico-mechanical properties in flow, we first need to understand these properties independent of their complex biology. The use of fully artificial biofilms, with controlled properties, based on mechanical properties of marine biofilms, can help achieve this.</p>
International journal of molecular sciences, Jan 10, 2018
The use of natural products (NPs) as possible alternative biocidal compounds for use in antifouli... more The use of natural products (NPs) as possible alternative biocidal compounds for use in antifouling coatings has been the focus of research over the past decades. Despite the importance of this field, the efficacy of a given NP against biofilm (mainly bacteria and diatoms) formation is tested with the NP being in solution, while almost no studies test the effect of an NP once incorporated into a coating system. The development of a novel bioassay to assess the activity of NP-containing and biocide-containing coatings against marine biofilm formation has been achieved using a high-throughput microplate reader and highly sensitive confocal laser scanning microscopy (CLSM), as well as nucleic acid staining. Juglone, an isolated NP that has previously shown efficacy against bacterial attachment, was incorporated into a simple coating matrix. Biofilm formation over 48 h was assessed and compared against coatings containing the NP and the commonly used booster biocide, cuprous oxide. Leac...
ABSTRACT Dstl and EPSRC have jointly funded a 3-year project at the University of Southampton to ... more ABSTRACT Dstl and EPSRC have jointly funded a 3-year project at the University of Southampton to develop corrosion detection and monitoring systems for land, marine and aerospace structures. By combining microfluidics with new, emerging sensor technologies, this project aims to develop in-situ systems that not only detect the onset of structural corrosion, but can also assess its state and apply appropriate remediation to inhibit its progress.
The search for new antifouling (AF) coatings that are environmentally benign has led to renewed i... more The search for new antifouling (AF) coatings that are environmentally benign has led to renewed interest in the ways that micro-organisms colonize substrates in the marine environment. This review covers recently published research on the global species composition and dynamics of marine biofilms, consisting mainly of bacteria and diatoms found on man-made surfaces including AF coatings. Marine biofilms directly interact with larger organisms (macrofoulers) during colonization processes; hence, recent literature on understanding the basis of the biofilm/macrofouling interactions is essential and will also be reviewed here. Overall, differences have been identified in species composition between biofilm and planktonic forms for both diatoms and bacteria at various exposure sites. In most studies, the underlying biofilm was found to induce larval and spore settlement of macrofoulers; however, issues such as reproducibility, differences in exposure sites and biofilm composition (natural multispecies vs. monospecific species) may influence the outcomes.
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Papers by Julian Wharton