From a circular economyperspective, one-pot strategies for theisolation of cellulose nanomaterials at a high yield and with multifunctionalproperties are attractive. Here, the effects of lignin content (bleachedvs unbleached softwood kraft pulp) and sulfuric acid concentrationon the properties of crystalline lignocellulose isolates and theirfilms are explored. Hydrolysis at 58 wt % sulfuric acid resulted inboth cellulose nanocrystals (CNCs) and microcrystalline celluloseat a relatively high yield (>55%), whereas hydrolysis at 64 wt% gaveCNCs at a lower yield (<20%). CNCs from 58 wt % hydrolysis weremore polydisperse and had a higher average aspect ratio (1.5-2x),a lower surface charge (2x), and a higher shear viscosity (100-1000x).Hydrolysis of unbleached pulp additionally yielded spherical nanoparticles(NPs) that were <50 nm in diameter and identified as lignin bynanoscale Fourier transform infrared spectroscopy and IR imaging.Chiral nematic self-organization was observed in films from CNCs isolatedat 64 wt % but not from the more heterogeneous CNC qualities producedat 58 wt %. All films degraded to some extent under simulated sunlighttrials, but these effects were less pronounced in lignin-NP-containingfilms, suggesting a protective feature, but the hemicellulose contentand CNC crystallinity may be implicated as well. Finally, heterogeneousCNC compositions obtained at a high yield and with improved resourceefficiency are suggested for specific nanocellulose uses, for instance,as thickeners or reinforcing fillers, representing a step toward thedevelopment of application-tailored CNC grades.

Selective laser melting (SLM) based processing of Mo-based samples is challenging due to solidification cracking. We here demonstrate that the addition of 2 wt% MoS2 to the Mo feedstock markedly improves crack mitigation of SLM-processed Mo/MoS2/Mo2S3 composite micro-lattice structures (SLM-Mo/ Mo(x)S(x+1)). Crack inhibition is suggested to be a result of Mo2S3 formation, decreased lattice strain (0.04 4%), and a decrease in accumulated residual stresses. The increased values of polarization resistance from 42.3 and 19.2 kU cm2 to 437 and 78.2 kU cm2, respectively verified the hindering effect of the composition on stress corrosion cracking (SCC) and surface oxidation cracking. However, an increased corrosion current density, from 1.22 to 10.2 mA/cm2, and cathodic Tafel constant, from 175 to 260.5 mV, confirmed the decreased polarization resistance and occurrence of different types of corrosion such as SCC and pitting. The strategy to add 2 wt% MoS2 to the Mo feedstock enables the fabrication of hightemperature micro-lattice structure components with improved corrosion resistance properties applicable in e.g., electronic, power semiconductor heat sinks, offshore-, aerospace-, defense-, or particularly novel sodium-ion energy storage applications.

The use of renewable wood-based fuel has been increasing in the last few decades because it is said to be carbon neutral. However, wood-based fuel, and especially used wood (also known as recycled wood or waste wood), is more corrosive than virgin wood (forest fuel), because of higher amounts of chlorine and heavy metals. These elements increase the corrosion problems at the furnace walls where the oxygen level is low.

Corrosion mechanisms are usually investigated at the superheaters where the temperature of the material and the oxygen level is higher than at the furnace walls.  Much less work has been performed on furnace wall corrosion in wood or used wood fired boilers, which is the reason for this project.    Tests are also mostly performed under simplified conditions in laboratories, making the results easier to interpret.  In power plants the interpretation is more complicated. Difficulties in the study of corrosion processes are caused by several factors such as deposit composition, flue gas composition, boiler design, and combustion characteristics and so on. Therefore, the laboratory tests should be a complement to the field test ones. This doctoral project involved in-situ testing at the furnace wall of power boilers and may thus contribute to fill the gap.

The base material for furnace walls is a low alloy steel, usually 16Mo3, and the tubes may be coated or uncoated. Therefore tests were performed both on 16Mo3 and more highly alloyed materials suitable for protective coatings.

Different types of samples exposed in used-wood fired boilers were analysed by different techniques such as LOM (light optical microscopy), XRD (X-ray diffraction), SEM (scanning electron microscopy), EDS (energy dispersive spectroscopy), WDS (wavelength dispersive spectroscopy), FIB (focused ion beam) and GD-OES (glow discharge optical emission spectroscopy). The corrosion rate was measured. The environment was also thermodynamically modelled by TC (Thermo-Calc ®).

The results showed that 16Mo3 in the furnace wall region is attacked by HCl, leading to the formation of iron chloride and a simultaneous oxidation of the iron chloride. The iron chloride layer appeared to reach a steady state thickness.  

Long term exposures showed that A 625 (nickel chromium alloy) and Kanthal APMT (iron-chromium-aluminium alloy) had the lowest corrosion rate (about 25-30% of the rate for 16Mo3), closely followed by 310S (stainless steel), making these alloys suitable for coating materials. It was found that the different alloys were attacked by different species, although they were exposed in the boiler at the same time in the same place. The dominant corrosion process in the A 625 samples seemed to be by a potassium-lead combination, while lead did not attack the APMT samples. Potassium attacked the alumina layer in the APMT samples, leading to the formation of a low-protective aluminate and chlorine was found to attack the base material.  The results showed that stainless steels are attacked by both mechanisms (Cl- induced attack and K-Pb combination).

Decreasing the temperature of the furnace walls of a waste wood fired boiler could decrease the corrosion rate of 16Mo3. However, this low corrosion rate corresponds to a low final steam pressure of the power plant, which in not beneficial for the electrical efficiency.

The short term testing results showed that co-firing of sewage sludge with used wood can lead to a reduction in the deposition of K and Cl on the furnace wall during short term testing. This led to corrosion reduction of furnace wall materials and coatings. The alkali chlorides could react with the aluminosilicates in the sludge and be converted to alkali silicates. The chromia layer in A 625 and alumina in APMT were maintained with the addition of sludge. 

The use of waste (or recycled) wood as a fuel in heat and power stations is becoming more widespread in Sweden (and Europe), because it is CO₂ neutral with a lower cost than forest fuel. However, it is a heterogeneous fuel with a high amount of chlorine, alkali and heavy metals which causes more corrosion than fossil fuels or forest fuel.

A part of the boiler which is subjected to a high corrosion risk is the furnace wall (or waterwall) which is formed of tubes welded together. Waterwalls are made of ferritic low-alloyed steels, due to their low price, low stress corrosion cracking risk, high heat transfer properties and low thermal expansion. However, ferritic low alloy steels corrode quickly when burning waste wood in a low NO_x environment (i.e. an environment with low oxygen levels to limit the formation of NO_x). Apart from pure oxidation two important forms of corrosion mechanisms are thought to occur in waste environments: chlorine corrosion and alkali corrosion.

Although there is a great interest from plant owners to reduce the costs associated with furnace wall corrosion very little has been reported on wall corrosion in biomass boilers. Also corrosion mechanisms on furnace walls are usually investigated in laboratories, where interpretation of the results is easier. In power plants the interpretation is more complicated. Difficulties in the study of corrosion mechanisms are caused by several factors such as deposit composition, flue gas flow, boiler design, combustion characteristics and flue gas composition. Therefore, the corrosion varies from plant to plant and the laboratory experiments should be complemented with field tests. The present project may thus contribute to fill the power plant corrosion research gap.

In this work, different kinds of samples (wall deposits, test panel tubes and corrosion probes) from Vattenfall’s Heat and Power plant in Nyköping were analysed. Coated and uncoated samples with different alloys and different times of exposure were studied by scanning electron microscopy (SEM), energy dispersive x-ray analysis (EDX), X-ray diffraction (XRD) and light optical microscopy (LOM). The corrosive environment was also simulated by Thermo-Calc software.

The results showed that a nickel alloy coating can dramatically reduce the corrosion rate. The corrosion rate of the low alloy steel tubes, steel 16Mo3, was linear and the oxide scale non-protective, but the corrosion rate of the nickel-based alloy was probably parabolic and the oxide much more protective. The nickel alloy and stainless steels showed good corrosion protection behavior in the boiler. This indicates that stainless steels could be a good (and less expensive) alternative to nickel-based alloys for protecting furnace walls.

The nickel alloy coated tubes (and probe samples) were attacked by a potassium-lead combination leading to the formation of non-protective potassium lead chromate. The low alloy steel tubes corroded by chloride attack. Stainless steels were attacked by a combination of chlorides and potassium-lead.

The Thermo-Calc modelling showed chlorine gas exists at extremely low levels (less than 0.1 ppm) at the tube surface; instead the hydrated form is thermodynamically favoured, i.e. gaseous hydrogen chloride. Consequently chlorine can attack low alloy steels by gaseous hydrogen chloride rather than chlorine gas as previously proposed. This is a smaller molecule than chlorine which could easily diffuse through a defect oxide of the type formed on the steel.

The use of waste wood as a fuel in power plants is becoming more widespread in Europe, because it is a renewable energy source with a lower cost than forest fuel. However it is more corrosive than coal and corrosion problems have arisen in the furnace wall area of a low NOx heat and power boiler. The furnace walls are made of a low alloy steel which has been coated in some parts with a nickel alloy to reduce corrosion. In this work, furnace tubes coated with a nickel alloy were compared to the uncoated tubes of the low alloy steel 16Mo3 after 3 years of exposure in the boiler. The nickel alloy coating and uncoated material were also compared with more controlled testing on a corrosion probe lasting for about 6 weeks. The corrosion rates were measured and the samples were chemically analysed by SEM/EDS/WDS and XRD methods. The corrosive environment was also modelled with Thermo-Calc software. The corrosion rates measured from the probe and tube samples of 16Mo3 agreed well with each other, implying linear corrosion rates. The results also showed that the use of nickel alloy coatings changes the corrosion mechanism, which leads to a dramatic reduction in the corrosion rate. The results are discussed in terms of the corrosion mechanisms and thermodynamic stability of the corrosion products.

The effect of digested sewage sludge as a fuel additive to reduce corrosion of furnace walls has been studied. The nickel base alloy Alloy 625 and the iron-chromium-aluminium alloy Kanthal APMT™ were exposed for 14.25. h at the furnace wall in a power boiler burning 100% used (also known as waste or recycled) wood. The test was then repeated with the addition of sewage sludge to the waste wood. The samples were chemically analysed and thermodynamically modelled and the corrosion mechanisms were investigated. The results showed that the co-firing of sewage sludge with recycled wood leads to a reduction in the corrosion. Attack by a potassium-lead combination appeared to be the main corrosion mechanism in Alloy 625 during waste wood combustion, while attack by alkali chloride was found to be dominant in APMT alloy.

Increasing use is being made of biomass as fuel for electricity production as the price of natural wood continues to rise. Therefore, more use is being made of waste wood (recycled wood). However, waste wood contains more chlorine, zinc and lead, which are believed to increase corrosion rates. Corrosion problems have occurred on the furnace walls of a fluidised bed boiler firing 100 % waste wood under low-NOx conditions. The deposits have been collected and analysed in order to understand the impact of the fuel.

Corrosion is a global problem which leads to both economicalct on the environment as well as other negative social and ethical aspects. Sodra Cell Monsteras, one of the largest producer of pulp in the world, suffers from corrosion problems in their evaporation plant.

Problems with corrosion can be handled with an effective material selection process, where suitable materials for specific conditions is discovered. The purpose with this report is to investigate the evaporation plant at Sodra Cell and its specific conditions, including environment and temperature. Also to investigate different types of corrosions common in pulp mills and how these can be prevented, as well as how materials behave under corrosive circumstances. The information is later to be used in a detailed material selection process, which is handled in this report but also should work as a foundation for Sodra Cell Monsteras for future material selections.

The material selection process in this report is performed according to Ashby's method, with CES Edupack as a supporting tool. The duplex steels, especially EN 1.4485 and EN 1.4362, showed to be the best suitable materials. However, to do a fair judgment and to choose one material, one should do a complete cost efficiency analysis, as well as decide a specific required pitting resistance equivalent number (PREN).

The effect of secondary hardening of tempered AISI 420 martensitic stainless steel on the corrosion behavior in aqueous 0.01 M NaCl has been studied, in-situ, using atomic force microscopy (AFM) to monitor real-time localized corrosion processes. Scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy, and X-ray diffraction analyses confirmed the presence of undissolved and secondary carbides (Cr23C6, Cr7C3, Cr3C2, Cr3C, Cr2C, and CrC) as well as retained austenite, all finely dispersed in the tempered martensitic matrix. Electrochemical measurements, consisted of monitoring of the open-circuit potential vs. time and cyclic polarization in 0.01 M NaCl solution, were performed to evaluate the passivity and its breakdown, and it was seen that initiation sites for localized corrosion were predominantly peripheral sites of carbides. In-situ AFM measurements revealed that there was a sequence for localized corrosion in which the neighboring matrix next to secondary carbides dissolved first, followed by corrosive attack on regions adjacent to undissolved carbides. Tempering at 500◦C reduced the corrosion resistance and the ability to passivate in comparison to tempering at 250◦C.

The resistance to environment-assisted cracking (EAC) of AISI 420 martensitic stainless steel (MSS) was investigated in 0.3 M NaCl solution (room temperature) at constant loads for 30 days. The steel tempered at 250 degrees C was superior to the 500 degrees C-temper, which showed corrosion pits favouring cracking. The fracture surface showed faceted grains, cleavage, striations, and inter- and transgranular cracks, suggesting a mixed stress corrosion cracking (SCC) and hydrogen embrittlement (HE) mechanism as the cause for EAC. Finite element modelling (FEM) indicated strain/stress localization at the mouth of deep pits and at the wall of shallow pits, displaying the favoured locations for pit-to-crack transition.

In this project a novel chitosan-stearic acid (CS-SA) coating with bee-pollen microcapsules for encapsulation of 2-mecraptobenzothiazole (MBT) as a waterborne formulation for a biocompatible corrosion protection coating was developed and the coating properties was analyzed. Hydrophobic stearic acid (SA) was crosslinked with via a carbodiimide reaction to form micelles and is assembled on the bee- pollen grains and the chitosan matrix was further self-crosslinked using glutaraldehyde (GA). Stearic acid was used to hydrophobically interact with modified pollen and with further crosslinking with the chitosan, which was proven successful by FTIR results. The encapsulation of anticorrosive agent MBT into pollen was successful and examined by UV-Vis spectroscopy, however, the pollen cannot form a fully stable formulation with the chitosan micelle matrix, partially due to its relatively big size (ca. 20 μm), causing problems with forming a proper barrier protection. The size of the grains and the interference of the carbodiimide crosslinking is the most severe problems with the pollen microcapsules. Therefore, no further testing of the corrosive properties could be done, which requires a dense and stable coating to sustain in salty water for the whole measurement period. As the reference coatings without pollen provided much more promising results, especially when crosslinked with GA, the conclusion is that the reactivity of the pollen is proven difficult to crosslink, and choosing a proper size of a microcontainer and the appropriate encapsulation method in the binder matrix is vital and important for developing a corrosion protective coating.

The corrosion resistance of nickel coatings on a copper substrate, plated from low-temperature electrolytes based on acetates, tartrates, and isobutyrates, was studied by the methods of electrochemical impedance spectroscopy (EIS) and polarization curves. The tests were performed in a 0.3% NaCl solution. The nickel coatings exhibit high chemical activity, dissolving in the NaCl solution. The electrochemical step is the limiting step of the corrosion process.

Corrosion is a mechanism that highly reduces the lifetime of metals in different environments, especially in water or moisture environment. The worldwide maintenance cost due to corrosion is estimated in billions of dollars per year, and actual solutions in terms of coating usually contains toxic or environmentally harmful species. With an always increasing restriction by environmental restraints and regulations, a sustainable solution is urgently needed.

Chitosan, easily obtained from chitin, the second most abundant biopolymer on earth, can be the solution to many problems. Crustacean shell waste is one of the major sources of chitin. Its resource efficiency, biocompatibility, and versatile physicochemical properties for chelation and crosslinking make chitosan a promising candidate as matrix material for biobased anticorrosive application.

The purpose of the Master Thesis is to combine the properties of chitosan with the high porosity of bee pollen as anticorrosive agent carrier to obtain a fully sustainable solution for anticorrosive protection. The objective of this very ambitious project is to produce a composite material with a triple action: anticorrosive protection of metal surfaces, self-healing property of the coating and anti- biofouling activity.

Results show that a biopolymer composite in forms of suspension or coatings with all desired components could be achieve. Specifically, a biopolymer nanocomposite composed of chitosan matrix, embedded with pollen grains that were loaded with anticorrosion agent 2- mercatobenzothiazole (MBT) in advance, and with zinc oxide nanoparticles have been produced.

The physicochemical characterization of the biopolymer composite and its coatings, as well as electrochemical impedance spectroscopy (EIS) measurements on stainless steel plate with such coatings, suggest that a uniform and compact coating is obtained. Despite its good hydrophobicity with maximum contact angle 134.32 ± 3.84° with top coating, the chitosan nanocomposite coating is still permeable to water, partially because of the relatively big size of pollen (ca. 20 μm) that introduces gaps and interferes integrity of the coating. Therefore, a full immersion corrosion resistance is not achieved. In conclusion, phase transfer of hydrophobic pollen into hydrophilic chitosan matrix, MBT loading in pollen, ZnO encapsulation in chitosan, as well as crosslinking of chitosan, were successfully carried out. A coating based on such biopolymer nanocomposite is prepared on stainless steel and investigated on its anti-corrosion property. Future work will be choosing a proper sized pollen as a microcontainer to enhance the integrity of the coating, and eventually endow the coating with the three-in-one function, i.e., anticorrosion, antimicrobial, and self-healing.

Reactions at the biointerfaces between stainless steel and protein-rich dairy products, which contain whey proteins, are important to consider in terms of food safety and material grade selection. Changes in corrosion behavior, metal release, and surface composition of austenitic (AISI 316 L), ferritic (AISI 430), and lean duplex (LDX 2101) stainless steels in simulated milk (SMS) and whey protein solution were investigated. The amount of released metals and the corrosion susceptibility increased according to 2101 < 316 L < 430. All grades revealed low corrosion rates in the whey protein solution without any sign of active/metastable corrosion. Pitting corrosion was evident for 430 in SMS. The total amount of released metals (iron, chromium, and nickel) was significantly higher in whey protein solution compared with SMS. This suggests the metal release process to be mainly governed by complexation reactions. Nickel was preferentially released compared to its bulk composition fraction for both 316 L and 2101 in the highly complexing SMS. Reduced metal release rates with time correlated with the enrichment of chromium in the surface oxide. The extent of metal release was for all metals substantially lower than release limits of metals stipulated in health regulations related to the use of alloys and metals in food-related environments.

Stainless steel is an important transport and processing contact material for bovine milk and dairy products. Release (migration) of metals, ions, complexes or wear debris/particles, and metal-induced protein aggregation in such environments are hence important to consider both from a corrosion and food safety perspective. This study aims on investigating the release of iron (Fe), chromium (Cr), and nickel (Ni) from AISI 316L stainless steel in contact with whey protein solutions relevant for protein drinks, and on how the whey proteins are influenced by stirring with a magnetic stir bar and metal release. Mechanistic insight is gained by parallel investigations of metal release from two reference non-protein containing solutions, a metal-complexing (citrate-containing) simulated milk solution (SMS) and a low complexing phosphate buffered saline solution (PBS). All immersion exposures were conducted at pH 6.8 for 0.5, 4, 24 and 48 hat room temperature at static and stirring conditions. All solutions and samples were investigated using different chemical, spectroscopic, microscopic, and electrochemical methods. Significantly higher amounts of Fe, Cr, and Ni were released into the whey protein solution (80 g/L) as compared to SMS and PBS. Strong enrichment of Cr in the surface oxide and reduction of the surface oxide thickness were associated with a higher amount of Ni release in the metal-complexing solutions (SMS and whey protein) compared with PBS. Stirring conditions resulted in higher amounts of metal release, enrichment of Cr in the surface oxide, and clear signs of wear of the 316L surface in all solutions compared to static conditions. The wear mechanism in the whey protein solution was different as compared to corresponding processes in SMS and PBS, involving an etching-like process and larger-sized wear debris. Electrochemical measurements at static conditions confirmed observed differences between the solutions, with the lowest corrosion resistance observed for coupons exposed in the whey protein solution, followed by SMS and PBS. Released metals in solution from the 316L coupons in contact with the whey protein solution resulted in enhanced rates of protein aggregation and precipitation of protein aggregates from solution. Further studies should be made to investigate other relevant test conditions and assess toxicological risks.

Hyaluronic acid and phospholipids are two components in the synovial joint cavity that contribute to joint lubrication synergistically. Molecular dynamics simulations were performed and hydrogen bonds in hyaluronic acid were analyzed to identify specific sites that are responsible for its physical cross-linking. Two molecular masses of hyaluronic acid, 10 kDa and 160 kDa, were considered. We use molecular dynamics simulations and the small world network approach to investigate dynamic couplings using a distance map applied to oxygen atoms in a chain of hyaluronic acid in the presence of phospholipids and water. The distance characterizing the coupling can be defined in various ways to bring out the most evident differences between various scenarios of the polymer chain conformation We show herein a physical distance understood as H-bond length and classes of these distances which are defined in a coarse-grained picture of the molecule. Simulation results indicate that addition of phospholipids has little influence on hyaluronic acid crosslinking. However, longer chains and addition of lipids promote appreciably long lasting (resilient) networks that may be of importance in biological systems. Specific sites for hydrogen bonding of phospholipids to hyaluronic acid have also been identified.

We have studied the energetics and mobility of neutral hydrogen in alumina Al2O3 using ab initio density-functional calculations. The mobility of hydrogen was studied in corundum (α-Al2O 3) as well as in liquid alumina. Using both static as well as molecular-dynamics calculations, and applying classical transition state theory, we derive the temperature-dependent diffusivity of hydrogen in α-Al 2O3 as D(T)=(21.7 × 10-8 m 2/s)exp(-1.24 eV/kT). The corresponding diffusivity of hydrogen in liquid/amorphous alumina, derived directly from ab initio molecular dynamics calculations, is D(T)=(8.71 × 10-7 m2/s)exp(-0.91 eV/kT). The computed diffusivity compares very well to experimental data. We conclude that diffusion of neutral hydrogen through the bulk of alumina is a good approximation of the mechanism for hydrogen mobility in corrosion scales. The representation of grain-boundary structures by amorphous alumina is, probably, realistic at higher temperatures.

A global transition towards more sustainable, affordable and reliable energy systems is being stimulated by the Paris Agreement and the United Nation's 2030 Agenda for Sustainable Development. This poses a challenge for the corrosion industry, as building climate-resilient energy systems and infrastructures brings with it a long-term direction, so as a result the long-term behaviour of structural materials (mainly metals and alloys) becomes a major prospect. With this in mind “Corrosion Challenges Towards a Sustainable Society” presents a series of cases showing the importance of corrosion protection of metals and alloys in the development of energy production to further understand the science of corrosion, and bring the need for research and the consequences of corrosion into public and political focus. This includes emphasis on the limitation of greenhouse gas emissions, on the lifetime of infrastructures, implants, cultural heritage artefacts, and a variety of other topics. 

Advanced alloys often present precipitated carbides and nitrides in their microstructure following exposure to elevated temperatures. These secondary phases are usually undesirable, because potentially deleterious for the corrosion and mechanical performances of the material. Carbides and nitrides are enriched in key alloying elements that are subtracted from their surrounding matrix areas, creating alloying element depleted zones, which might become initial sites for corrosion initiation. In this study, the influence of micro- and nano-sized precipitated carbides and nitrides on the corrosion initiation of biomedical CoCrMo alloys and duplex stainless steels has been investigated at microscopic scale, by using a combination of local probing techniques. The microstructures of the alloys were first characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM) and magnetic force microscopy (MFM). The Volta potential mapping of carbides and nitrides revealed their higher nobility compared to the matrix, and particularly compared to their surrounding areas, suggesting the occurrence of some alloying element depletion in the latter locations, which may lead to a higher susceptibility for corrosion initiation. In-situ electrochemical AFM studies performed at room temperature showed passive behavior for large potential ranges for both alloy families, despite the presence of the precipitated carbides or nitrides. At high anodic applied potential, at which transpassive dissolution occurs, preferential dissolution started from the areas adjacent to the precipitated carbides and nitrides, in accordance with the Volta potential results. Thus, the presence of carbides and nitrides doesn’t largely affect the corrosion resistance of the tested advanced alloys, which maintain passive behavior when exposed to highly concentrated chloride solutions at room temperature with no applied potential. The effect of nitrides on the corrosion initiation of duplex stainless steels was investigated also at temperatures above the critical pitting temperature (CPT). Depending on the type, distribution and size range of the precipitated nitrides different corrosion behaviors were observed. Intragranular (quenched-in) nano-sized nitrides (ca. 50-100 nm) finely dispersed in the ferrite grains have a minor influence on the corrosion resistance of the material at temperatures above the CPT, while larger intergranular (isothermal) nitrides (ca. 80-250 nm) precipitated along the phase boundaries cause a detrimental reduction of the corrosion resistance of the material, in particular of the austenite phase

Chromium nitrides may precipitate in duplex stainless steels during processing and their influence on the corrosion behavior is of great importance for the steel performance. In this study, the influence of nano-sized quenched-in chromium nitrides on the corrosion behavior of a heat treated 2205 duplex stainless steel was investigated at room temperature and 50 °C (just above critical pitting temperature). The microstructure was characterized by SEM/EDS and AFM analyses, and quenched-in nitrides precipitated in the ferrite phase were identified by TEM analysis. Volta potential mapping at room temperature suggests lower relative nobility of the ferrite matrix. Electrochemical polarization and in-situ AFM measurements in 1 M NaCl solution at room temperature show a passive behavior of the steel despite the presence of the quenched-in nitrides in the ferrite phase, and preferential dissolution of ferrite phase occurred only at transpassive conditions. At 50 °C, selective dissolution of the austenite phase was observed, while the ferrite phase with the quenched-in nitrides remained to be stable. It can be concluded that the finely dispersed quenched-in nitrides do not cause localized corrosion, whereas the exposure temperature has a strong influence on the corrosion behavior of the duplex stainless steel.

Precipitation of different types of chromium nitrides may occur during processing of super duplex stainless steels, affecting the properties of the material. In this study the influence of quenched-in (size range ca. 50-100 nm) and isothermal (size range ca. 80-250 nm) types of nitrides on the corrosion behavior of a 2507 super duplex stainless steel has been investigated at room temperature and at 90 degrees C (above the critical pitting temperature) in 1 M NaCl solution. The microstructure has been characterized by scanning electron microscopy and magnetic force microscopy. The isothermal nitrides exhibit a higher Volta potential compared to the matrix, but such difference could not be observed for the quenched-in nitrides. In-situ electrochemical AFM measurements at room temperature show stable surfaces for a wide range of applied potentials despite the presence of either type of nitrides. In the transpassive region isothermal nitrides appear to be slightly more deleterious than quenched-in nitrides. At 90 degrees C isothermal nitrides largely reduce the corrosion resistance of the austenite phase, while the quenched-in nitrides reduce the corrosion resistance of the material to a much lesser extent. The size difference between isothermal and quenched-in chromium nitrides may be crucial, in particular above the critical pitting temperature.

The “transpassive” behavior of a CoCrMo alloy has been investigated to clarify the nature of the current increase at high anodic potential (0.5-0.7 VAg/AgCl). The total amount of released metal ions was determined after the potentiostatic measurements. According to the calculation through Faradays’ law, the metal dissolution only contributes to part of the total current recorded. Electrochemical AFM mapping did not show pronounced topography changes at 0.65 VAg/AgCl, while light optical microscopy observation revealed fast evolution of oxygen bubbles. Evidently water oxidation is another important process largely contributing to the current increase at the high potential.

Correction for 'Physical crosslinking of hyaluronic acid in the presence of phospholipids in an aqueous nano-environment' by Piotr Bełdowski et al., Soft Matter, 2018, DOI: 10.1039/c8sm01388h. 

In this Master of Science thesis screws with different coatings were exposed to an accelerated corrosion test in order to investigate the corrosion development. The test matrix constituted of hexagonal and flange screws (fastened on frames) coated with either zinc/iron (ZnFe) or a flake system of aluminum and zinc (GEOMET). The corrosion results were analyzed by means of X-ray diffraction (XRD). In this study the screws were also crosscut and analyzed by means of FEG-SEM in order to determine the thickness and the elemental content of the surface coating. The result of the corrosion test showed that the screws coated with GEOMET showed a very good corrosion resistance whilst the screws coated with ZnFe failed to fulfill the demands on corrosion resistance of Scania.

Copper and copper-based alloys are commonly used in both ancient and modern architecture. This requires an in-depth fundamental and applied understanding on their atmospheric corrosion behavior at different climatic, environmental and pollutant levels and how these parameters influence e.g. corrosion initiation, patina characteristics, aesthetic appearances, corrosion rates, and runoff rates. This doctoral thesis elucidates the role of native surface oxides on the corrosion performance, corrosion initiation, formation and evolution of corrosion products from hours to months, years and even centuries, to diffuse dispersion of metals from Cu metal/Cu alloy surfaces focusing on the roles of alloying elements, microstructure, and deposition of chlorides. In-depth investigations have been performed at both laboratory and field conditions on commercial Cu metal and copper-based alloys of a golden alloy (Cu5Zn5Al1Sn) and Sn-bronzes (Cu4Sn, Cu6Sn). Patina characteristics and relations to the presence of microstructural inclusions have in addition been investigated for historic patinas of Cu metal roofing of different age and origin, highlighted with data for a 400 years old Cu patina exposed at urban conditions.

A multi-analytical approach comprising microscopic, spectroscopic and electrochemical methods was employed for in-depth investigations of surface characteristics and bulk properties. Electron backscattered diffraction (EBSD) was utilized to characterize the microstructure. Auger electron spectroscopy (scanning-AES), X-ray photoelectron spectroscopy (XPS), glow discharge optical emission spectroscopy (GDOES) were employed for surface chemical compositional analysis, and atomic absorption spectroscopy (AAS) to assess the amount of metal release from the patinas. Cathodic reduction (CR) and electrochemical impedance spectroscopy (EIS) were used to assess the amount and corrosion resistance of corrosion products formed at laboratory conditions. Confocal Raman micro-spectroscopy (CRM), infrared reflection absorption spectroscopy (IRAS) and grazing incidence X-ray diffraction (GIXRD) were used to identify the phases of corrosion products. Colorimetry was used to assess surface appearances.

Cu5Zn5Al1Sn and Cu4Sn/Cu6Sn exhibit favorable bulk properties with respect to corrosion in terms of smaller grain size compared with Cu metal and show non-significant surface compositional variations. The presence of multi-component native oxides predominantly composed of Cu₂O enriched with Sn-oxides on Cu4Sn/Cu6Sn, and with ZnO, SnO₂ and Al₂O₃ on Cu5Zn5Al1Sn, improves the barrier properties of the native surface oxides and the overall corrosion resistance of Cu4Sn/Cu6Sn and Cu5Zn5Al1Sn. The formation of Zn/Al/Sn-containing corrosion products (e.g. Zn₅(CO₃)₂(OH)₆ and Zn₆Al₂(OH)₁₆CO₃·4H₂O) significantly reduces the corrosion rate of Cu5Zn5Al1Sn in chloride-rich environments. Alloying with Sn reduces the corrosion rate of Sn-bronze at urban environments of low chloride levels but results in enhanced corrosion rates at chloride-rich marine conditions.

A clear dual-layer structure patina was observed for centuries-old naturally patinated copper metal with an origin from the roof of Queen Anne's Summer Palace in Prague, the Czech Republic. The patina comprises an inner sub-layer of Cu₂O and an outer sub-layer of Cu₄SO₄(OH)₆/Cu₃SO₄(OH)₄. Abundant relatively noble inclusions (mainly rosiaite (PbSb₂O₆)) were observed and incorporated in both the copper matrix and the patina. The largest inclusions of higher nobility than the surrounding material create significant micro-galvanic effects that result in a fragmentized patina and large thickness ratios between the Cu₄SO₄(OH)₆/Cu₃SO₄(OH)₄ and the Cu₂O sub-layer, investigated via a statistical analysis of inclusions and patina characteristics of eight different historic urban copper patinas.

The effect of blue light on atmospheric corrosion of Cu and on the antimicrobial properties was explored upon exposure mimicking the condition of hygienic surface disinfection. The results show that blue light illumination enhanced the formation of Cu2O, resulting in a slightly increased corrosion resistance of Cu without pre-deposited NaCl, whereas the enhanced formation of Cu2O, CuCl and/or Cu(OH)3Cl on copper with pre-deposited NaCl caused concomitant corrosion product flaking and a reduced corrosion resistance. The blue light induced enhancement of Cu corrosion led to increased surface roughness and more pronounced integration of bacteria within the corrosion products.

The complex stratified patina formed on Sn-bronze in chloride-rich atmospheres has been explored through long-term field exposures and short-term laboratory investigations using a multi-analytical approach. The stratified patina is composed of Cu2O- and Cu-2(OH)(3)Cl-rich sublayers intercalated by Sn-oxides, mainly SnO2. The stratification is triggered by events of high chloride deposition, resulting in repeated dissolution and solidification of sublayers, whereby redox reactions between the intermediate products of Sn- and Cu-chlorides play a crucial role. Sn-induced patina stratification is a major reason for enhanced patina flaking on Sn-bronze and its accelerated corrosion rate compared to Cu metal in marine environments.

The morphology and elemental composition of cross sections of eight historic copper materials have been explored. The materials were taken from copper roofs installed in different middle and northern European environments from the 16th to the 19th century. All copper substrates contain inclusions of varying size, number and composition, reflecting different copper ores and production methods. The largest inclusions have a size of up to 40 μm, with most inclusions in the size ranging between 2 and 10 μm. The most common element in the inclusions is O, followed by Pb, Sb and As. Minor elements include Ni, Sn and Fe. All historic patinas exhibit quite fragmentized bilayer structures, with a thin inner layer of cuprite (Cu2O) and a thicker outer one consisting mainly of brochantite (Cu4SO4(OH)6). The extent of patina fragmentation seems to depend on the size of the inclusions, rather than on their number and elemental composition. The larger inclusions are electrochemically nobler than the surrounding copper matrix. This creates micro-galvanic effects resulting both in a profound influence on the homogeneity and morphology of historic copper patinas and in a significantly increased ratio of the thicknesses of the brochantite and cuprite layers. The results suggest that copper patinas formed during different centuries exhibit variations in uniformity and corrosion protection ability.

This paper focuses on the study of micro-galvanic corrosion of the Cu/Ru couple in KIO4 solution. Practical nobility across the Cu/Ru interface was evaluated by Volta potential mapping, and the morphological changes were monitored by in-situ atomic force microscopy measurements during exposure in a KIO4 solution. Chemical composition of precipitated corrosion product was analyzed by Confocal Raman spectroscopy immediately after the exposure. The results show that Cu is the anode of the Cu/Ru couple, and accelerated dissolution of Cu preferentially occurs near the Cu/Ru interface. However, subsequent formation of insoluble Cu(IO3)2·nH2O leads to precipitation, which impedes further Cu corrosion.

The military vehicle, Pansarterrängbil 203 (PATGB 203) demonstrates a fault. There are some components in a coolant circuit that fail due to corrosion while others are unaffected. One of the affected components that will be investigated in this report is the water heater. The subject of this technical investigation has been an issue for FMV, Swedish Defence Materiel Administration since a decade. While seeking out the cause of the coolant circuit failing, this investigation aim to analyzing the underlying problems considering material, factors of corrosion and organization.

In order to establish the origin of material and appearance of corrosion, experiments were performed. The experiments showed that the original material is an Al-Si alloy. The micrographs indicated varying stratification of the corrosion throughout the unit. The corrosive deposits consisted mainly of oxygen, silicon, aluminum and sodium.

Consequently, the protecting passive oxide layer is compromised, which results in a direct connection between the coolant and the underlying material. This direct connection gives rise to the development of corrosion in the material. Clear underlying causes of the corrosion were not found but the most probable suggest on galvanic corrosion accelerated by a stray current. Properly grounding the components decreases the stray current in the system and is essential to avoid corrosion. If grounding the components is not sufficient, additional checks of the coolant with attention to the pH-value and the function of corrosion inhibitors may indicate corrosion at an earlier stage.

A lean-alloyed FeCrAl steel have been developed by KTH and Kanthal and tested in liquid lead environments at 800°C and 900°c, as well as at 550°C with and without impurities and varying oxygen activates. The results demonstrate that the lean alloyed FeCrAl steel shows superior oxidation performance up 800°C. Also, lead impurities can accelerate corrosion.

The aim of the work has been to study the corrosion resistance of a new low alloyed experimental FeCrAl steel, with the potential use as corrosion barrier in high temperature lead based energy applications. The exposures were conducted in liquid lead at 800 degrees C and 900 degrees C, with controlled oxygen environment, for up to 1760 h. The results demonstrate that the new experimental alloy had formed a protective oxide in both exposures, with no indications of lead penetration. The alloy showed better corrosion properties than that of the reference materials: Kanthal APMT, Kanthal APMTT and AISI 316L. This indicates that the ductile Fe-10Cr-4Al-RE steel can be used as a corrosion barrier in liquid lead based clean energy applications, operating at very high temperatures.

To investigate aging effect on the passive film of Ni23Cr15Mo and Ni22Cr9Mo3Nb, synchrotron-based X-ray photoelectron spectroscopy (XPS) was used to analyze the structure and composition of the air-formed passive film on the alloys. The corrosion resistance of the two Ni alloys in 1 M NaCl solution was evaluated with electrochemical cyclic polarization measurement. The synchrotron XPS measurement provided detailed information about chemical states of alloying elements in the passive film, showing that the passive film consists of an inner oxide layer and an outer hydroxide layer. The XPS data allowed precise determination of the chemical composition and the thickness of the outer hydroxide layer, the inner oxide layer, and the underlying subsurface alloy layer. The Cr-oxide in the inner layer grows thicker with aging time, leading to Cr-depletion in the subsurface region. Mo and Nb in the alloy form mixed oxides and hydroxides, and aging in air leads to transformation of the lower valence oxides into higher valence oxides. The freshly formed oxide film exhibits similar barrier properties as the aged oxide film. The stability of the passive film formed on Ni22Cr9Mo3Nb seems to be better than that on Ni23Cr15Mo.

Generation IV nuclear power technologies provide attractive solutions to the common issues related to conventional nuclear power plants currently in operation worldwide. Through a significant reduction of the long-term radiotoxicity of nuclear waste, a more efficient use of nuclear fuel resources, and implementation of inherent safety features, Generation IV will make nuclear power sustainable and thus increase the public acceptance of nuclear power. Due to its attractive safety features, the lead-cooled fast reactor (LFR) is one of the most studied Generation IV reactor concepts currently. It is well known that liquid lead is corrosive to steels at elevated temperatures, thus limiting the operation temperature of the LFR. The use of alumina-forming FeCrAl alloys has been proposed to mitigate oxidation and corrosion issues. Commercial FeCrAl alloys have Cr-concentrations typically about 20 wt. % and are thus prone to α-α’ phase separation and embrittlement at temperatures up to about 500 °C. Reducing the Cr-concentration to levels around 10 wt. % would theoretically resolve the said issue. However, the oxidation and corrosion resistance may be impaired. In the scientific literature, compositional limits indicating the formation of protective alumina layers at various temperatures have been presented. Long-term corrosion studies are however scarce. Moreover, in-depth studies on the compositional limits regarding α-α’ phase separation are lacking. In this thesis, the long-term (up to 10,000 h) corrosion resistance and phase stability of alumina-forming alloys are studied at temperatures up to 550 °C. In addition, the influence of reactive elements (RE), e.g. Ti, Zr, and Y, on the liquid lead corrosion resistance of Fe10CrAl alloys is evaluated. By balancing the reactive element and the carbon content, with respect to carbide formation, it is demonstrated in this thesis that it is possible to form protective alumina layers on Fe10Cr4Al alloys from 450 °C, despite the low Al and Cr concentrations. It was found that the RE/carbon ratio needed to form protective alumina layers on Fe10Cr4Al alloys must be larger than unity to mitigate the detrimental effect of Cr-carbide formation.  The underlying phenomena are discussed, and a mechanism is suggested based on the outcome of the long-term oxidation studies. The phase stability of Fe10CrAl alloys was studied through thermal aging experiments in the temperature interval of 450 to 550 °C. In addition, the results were well reproducible using a developed Kinetic Monte Carlo (KMC) model of the FeCrAl system. Furthermore, the model indicated that the Cr-concentration should be limited to about 11 wt. % in a FeCr4Al alloy to mitigate α-α’ phase separation at all temperatures of interest for an LFR. The liquid lead corrosion resistance of alumina-forming austenitic stainless steels was shown to be superior compared to regular stainless steels, albeit the effect of ferrite stabilizing elements needs to be further addressed. The results included in this thesis provide a valuable input on the key issues related to the development of corrosion resistant alumina-forming alloys of interest for liquid lead applications. Moreover, the superior oxidation properties of the studied alumina-forming alloys make them of interest for use in other energy applications, where corrosion issues limits the operation temperature and thus the efficiency.

Iron–Chromium–Aluminium (Fe–Cr–Al) alloys have been widely investigated as candidate materials for various nuclear applications. Albeit the excellent corrosion resistance, conventional Fe–Cr–Al alloys suffer from α–α′ phase separation and embrittlement when subjected to temperatures up to 500 °C, due to their high Cr-content. Low-Cr Fe–Cr–Al alloys are anticipated to be embrittlement resistant and provide adequate oxidation properties, yet long-term aging experiments and simulations are lacking in literature. In this study, Fe–10Cr–(4–8)Al alloys and a Fe–21Cr–5Al were thermally aged in the temperature interval of 450–550 °C for times up to 10,000 h, and the microstructures were evaluated mainly using atom probe tomography. In addition, a Kinetic Monte Carlo (KMC) model of the Fe–Cr–Al system was developed. No phase separation was observed in the Fe–10Cr–(4–8)Al alloys, and the developed KMC model yielded results in good agreement with the experimental data.

Due to coming emission legislations, the temperature is expected to increase in heavy-duty diesel engines, specifically in the hot-end of the exhaust system affecting components, such as exhaust- and turbo manifolds. Since the current material in the turbo manifold, a ductile cast iron named SiMo51, is operating close to its limits there is a need for material development in order to maintain a high durability of these components. When designing for increased life, many material properties need to be considered, for example, creep-, corrosion- and fatigue resistance. Among these, the present work focuses on the latter two up to 800°C improving the current material by additions of Cr, for corrosion resistance, and Ni, for mechanical properties. The results show improved high-temperature corrosion resistance in air from 0.5 and 1wt% Cr additions resulting in improved barrier layer at the oxide/metal interface. However, during oxidation in exhaust-gases, which is a much more demanding environment compared to air, such improvement could not be observed. Addition of 1wt% Ni was found to increase the fatigue life up to 250°C, resulting from solution strengthening of the ferritic matrix. However, Ni was also found to increase the oxidation rates, as no continuous SiO₂-barrier layers were formed in the presence of Ni. Since none of the tested alloys showed improved material properties in exhaust gases at high temperature, it is suggested that the way of improving performance of exhaust manifolds is to move towards austenitic ductile cast irons or cast stainless steels. One alloy showing good high-temperature oxidation properties in exhaust atmospheres is an austenitic cast stainless steel named HK30. This alloy formed adherent oxide scales during oxidation at 900°C in gas mixtures of 5%O₂-10%H₂O-85%N₂ and 5%CO₂-10%H₂O-85%N₂ and in air. In the two latter atmospheres, compact scales of (Cr, Mn)-spinel and Cr₂O₃ were formed whereas in the atmosphere containing 5%O₂ and 10%H₂O, the scales were more porous due to increased Fe-oxide formation. Despite the formation of a protective, i.e. compact and adherent, oxide scale on HK30, exposure to exhaust-gas condensate showed a detrimental effect in form of oxide spallation and metal release. Thus, proving the importance of taking exhaust-gas condensation, which may occur during cold-start or upon cooling of the engine, into account when selecting a new material for exhaust manifolds. 

The colloidal self-assembly of plasmonic gold nanoparticles (AuNPs) is of interest to utilize the plasmonic coupling effects that arise between nanoparticles. The enhanced properties of anisotropic AuNPs make them particularly attractive in self-assemblies. Herein, a literature study into the different strategies used to obtain self-assemblies of AuNPs using molecular linkers is presented. The use of nanospheres (AuNS) and nanorods (AuNRs) were mainly reviewed. Thereafter, two different nanobipyramids (AuBPs) were investigated for use in self-assemblies. The concentration of cetyltrimethylammonium bromide (CTAB), which coats the AuNP surface, was manipulated to study the stability of the AuNPs. A stable, meta-stable and non-stable region were identified for the nanoparticles. At low CTAB levels, the AuNPs preferentially assemble end-to-end. The addition of L-cysteine to stable AuNP dispersion induced end-to-end assembly, showing promise as a molecular linker for AuBPs. The addition of excess CTAB stabilized the assemblies over time. The kinetic behaviour of the two AuBPs differed, suggesting the effect of the AuNP shape on the self-assembly kinetics. This study provides a starting point for the development of a robust self-assembly strategy for anisotropic AuNPs by using L-cysteine as a molecular linker.

This work describes the chemical, mechanical and antibacterial properties of a novel silver nanocluster/silica composite coating, obtained by sputtering, on textiles for use in nuclear bacteriological and chemical (NBC) protection suites and for aerospace applications.

The properties of the coated textiles were analyzed in terms of surface morphology, silver concentration and silver release in artificial sweat and synthetic tap water, respectively. No release of silver nanoparticles was observed at given conditions.

The water repellency, permeability, flammability and mechanical resistance of the textiles before and after sputtering demonstrated that the textile properties were not negatively affected by the coating.

The antibacterial effect was evaluated at different experimental conditions using a standard bacterial strain of Staphylococcus aureus and compared with the behavior of uncoated textiles.

The coating process conferred all textiles a good antibacterial activity. Optimal deposition conditions were elaborated to obtain sufficient antibacterial action without altering the aesthetical appearance of the textiles.

The antibacterial coating retained its antibacterial activity after one cycle in a washing machine only for the Nylon based textile.

Self-assembled monolayers of octadecanethiol (ODT) have previously shown to provide excellent corrosion inhibition on copper exposed to humidified air containing formic acid, mimicking indoor atmospheric corrosion. ODT layers are, however, much less efficient corrosion inhibitors for zinc. In this work, we elucidate the possibility of using ODT monolayers to inhibit corrosion of brass. Based on a quantitative analysis of corrosion products, we found that ODT provides equally good corrosion inhibition of single-phase Cu20Zn as of pure copper, retarding the transportation of corrosion stimulators to the brass surface. On double-phase Cu40Zn, however, local galvanic effects led to less efficient corrosion inhibition and more corrosion products than on Cu20Zn.

Due to new regulations for the use of brass in contact with drinking water, new lead-free brass alloys have been developed. It is therefore of great interest to investigate their corrosion properties in terms of dezincification resistance. An accelerated standard test, SS-EN ISO 6509-1:2014 is used to determine the dezincification resistance of brass alloys. However, as this standard test was developed for leaded brass alloys, it has not yet been established whether this method also is suitable to assess the dezincification resistance of lead-free brass alloys. 

This master thesis study aimed to expand this knowledge gap by investigating how the dezincification properties of three different brass alloys, two newly developed lead-free alloys and one lead-containing alloy, were affected by changing the parameters of the standard test. The results were compared with their behaviour in tap water to determine the reliability of the ISO test. Most of the obtained results of the lead-free brass alloys were in accordance with the results obtained for the leaded brass alloy. It could therefore be concluded that the standard test can be used to assess the dezincification resistance of brass alloys and also reflect their ranking at tap water conditions.

Due to new regulations for the use of brass in contact with drinking water, new lead-free brass alloys have been developed. It is therefore of great interest to investigate their corrosion properties in terms of dezincification resistance. An accelerated standard test, SS-EN ISO 6509-1:2014 is used to determine the dezincification resistance of brass alloys. However, as this standard test was developed for leaded brass alloys, it has not yet been established whether this method also is suitable to assess the dezincification resistance of lead-free brass alloys. 

This master thesis study aimed to expand this knowledge gap by investigating how the dezincification properties of three different brass alloys, two newly developed lead-free alloys and one lead-containing alloy, were affected by changing the parameters of the standard test. The results were compared with their behaviour in tap water to determine the reliability of the ISO test. Most of the obtained results of the lead-free brass alloys were in accordance with the results obtained for the leaded brass alloy. It could therefore be concluded that the standard test can be used to assess the dezincification resistance of brass alloys and also reflect their ranking at tap water conditions.

The excellent corrosion resistance of stainless steels arises from the presence of a passive film on its surface. Above 10.5wt% Cr a chromium oxide of 1-3 nm is formed on the surface of the metal that in case of damage will reform and hinder further dissolution of the metal. However, the passivity of the stainless steel can be altered by material factors and external factors; such as the composition of the underlying phases, external loads or thermal treatments.

In this work the local electrochemical techniques Scanning Vibrating Electrode Technique (SVET) and Scanning Kelvin Probe Force Microscopy (SKPFM) and the local characterization techniques X-ray Photoelectron Spectroscopy (XPS) and Auger Electron Spectroscopy (AES) have been used to investigate corrosion phenomena of stainless alloys based on measurements of corrosion current density, work function, thickness and composition of the oxide.

The effect on work function of the thickness of the passive film and composition of the underlying phases was investigated for 301LN austenitic stainless steel (Paper I) and a heat treated superduplex 25Cr7Ni type stainless steel (Paper II). It was shown that the work function can be an indicator of corrosion resistance of the phases in the microstructure, and that the composition of the underlying phases had a greater effect on the work function than the thickness of the passive film.

External factors such mechanical deformation (Paper I) and welding (Paper III) altered the passivity of the steel and work function. It was found that plastic deformation decreased irreversibly the work function, whereas elastic deformation did not have any permanent effect. Thermal oxides affected the passivity of stainless steels welded joints and were detrimental for its corrosion resistance. Anodic activity, observed with SVET, and pitting corrosion were detected at the heat tint and attributed to the interaction between the composition and the thickness of the oxide. Brushing combined with pickling was recommended for recovering the passivity of stainless steels.

Several factors during steel manufacture and fabrication can alter the passivity and corrosion behaviour of stainless steels. These include alloying, deformation, welding and heat treatments.

In this work a combination of local techniques, such as Scanning Vibrating Electrode Technique (SVET) and Scanning Kelvin Probe Force Microscopy (SKPFM), and surface and microstructural analytical techniques, such as Electron Backscatter Diffraction (EBSD), Auger Electron Spectroscopy (AES) and X-ray Photoelectron Spectroscopy (XPS) is used to elucidate the influence of process variables on the corrosion resistance of stainless steels. Different manufacturing processes, such as casting, rolling or additive manufacturing (AM) (Paper V), fabrication processes, such as welding (Paper III) and deformation (Paper I and IV), and post-processing, such as heat and high pressure treatments (Paper II and V) and post-weld cleaning (Paper II) are studied.

The results showed that deformation can have a major impact on microstructure but a smaller impact on corrosion. Plastic deformation decreased irreversibly the Volta potential, whereas elastic deformation did not have any permanent effect. The potential was dependent on composition, passive film thickness and deformation but not on the crystallographic orientation. Thermal oxides formed after welding were detrimental to corrosion resistance. SVET showed anodic activity on the weld areas with oxides where pitting initiated, explained by the interplay between the composition and the thickness of the oxides. Brushing combined with pickling was recommended for restoring the corrosion resistance. Long-term ageing of a Cu-alloyed 2507 caused precipitation of Cu-rich ε particles which showed the lowest potential and were most severely pitted, plus nitrides which were the most noble. Intermetallic sigma phase observed in the AM 2507 after HIP heat treatment with slow cooling resulted in a decreased corrosion resistance. However, it was concluded that AM 2507 exhibits similar or even higher corrosion resistance than conventional 2507 if appropriate post-processing parameters are applied.

This thesis provides scientific insights to facilitate the correct manufacturing, fabrication and use of stainless steels. 

The aim of the present work was to study the influence of the stress on the electrode potential of the austenitic stainless steel301LN using Scanning Kelvin Probe (SKP). It was found that elastic deformation reversibly ennobles the potential whereas plasticdeformation decreases the potential in both tensile and compressive deformation mode and this decrease is retained even 24 h afterremoval of the load. To interpret the stress effects, different surface preparations were used and the composition and thickness ofthe passive film were determined by GDOES. Slip steps formed due to plastic deformation were observed using AFM. The effect ofplastic strain on the potential is explained by the formation of dislocations, which creates more a defective passive film.

In this work the influence of copper (0–4 wt%) on the microstructure, passive film properties and local electrochemical response of 25Cr7Ni-type duplex stainless steel is investigated after long term heat-treatment at 800◦C for 6 months. This heat-treatment was done to promote the formation of different phases which could be studied in terms of passive film properties and electrochemical response. The unique microstructures of the alloys comprise austenite, sigma phase, Cr2N nitrides and, for the 2 wt% and 4 wt% Cu alloys, epsilon-Cu phase. The results show that alloying with Cu increases slightly the amount of isothermal Cr2N nitrides and epsilon-Cu phase, but decreases the sigma phase fraction. The location of pitting corrosion as well as the Electrochemical Potential (EP), or electron work function, measured with Scanning Kelvin Probe Force Microscopy (SKPFM) show that the epsilon-Cu phase has the lowest corrosion resistance. The EP appears to depend more on the composition of the underlying phase than on the thickness of the passive film. Cr-nitrides have the highest EP followed by sigma phase, austenite and epsilon-Cu phase. There is a clear decrease of EP of the austenitic phase when 2 wt% Cu is added in the alloy.