Search

The grain boundary character distribution (GBCD) in an austenitic stainless steel produced by additive manufacturing (AM) in both as-built and annealed conditions was studied. Relatively fine grains and a non-fibre texture was achieved by AM, and as-built structure showed a high population of Σ3 boundaries. A five-parameter GBCD analysis revealed that the microstructure is mostly dominated by highly incoherent Σ3 boundaries. The grain boundary network also consisted of random high angle, coherent Σ3s terminating on (111) planes with a pure twist character, and tilt Σ9 boundaries. The findings show prospects for the possibility of engineering the grain boundary network of materials in-situ, via the stress and heat induced by the thermal cycles during AM.

Metal additive manufacturing (AM) refers to any process of making 3D metal parts layer-upon layer via the interaction between a heating source and feeding material from a digital design model. The rapid heating and cooling attributes inherent to such an AM process result in het erogeneous microstructures and the accumulation of internal stresses. Post-processing heat treatment is often needed to modify the microstructure and/or alleviate residual stresses to achieve properties comparable or superior to those of the conventionally manufactured (CM) counterparts. However, the optimal heat treatment conditions remain to be defined for the ma jority of AM alloys and are becoming another topical issue of AM research due to its industrial importance. Existing heat treatment standards for CM metals and alloys are not specifically designed for AM parts and may differ in many cases depending on the initial microstructures and desired properties for specific applications. The purpose of this paper is to critically review current knowledge and discuss the influence of post-AM heat treatment on microstructure, me chanical properties, and corrosion behavior of the major categories of AM metals including steel, Ni-based superalloys, Al alloys, Ti alloys, and high entropy alloys. This review clarifies significant differences between heat treating AM metals and their CM counterparts. The major sources of differences include microstructural heterogeneity, internal defects, and residual stresses. Under standing the influence of such differences will benefit industry by achieving AM metals with consistent and superior balanced performance compared to as-built AM and CM metals.

Research into non-toxic rare earth metal organic compounds providing an alternative to chromates as corrosion inhibitors was pioneered by research at Monash University almost 20 years ago. Further ...

Depletion depths of inorganic components from a scribe edge in a polyurethane primer containing Li2CO3, MgO, BaSO4 and TiO2 beneath a topcoat, were determined using a range of techniques including SEM/EDS and proton induced X-ray and γ-ray emission spectroscopies. SEM of sections cut using an ion beam revealed scribe damage penetrating 20–25 μm away from the scribe edge prior to leaching. After neutral salt spray (NSS) exposure a leached zone developing from the scribe edge was observed. For longer NSS exposure times (>96 h) this leached zone of nearly complete Li and Mg depletion did not develop any deeper than the scribe damaged region indicating that the depletion zone was caused by mechanical damage due to scribing. At short times small voids were formed in Li2CO3 particles within the primer well away from the scribe (100–260 μm) whereas a mixture of void and detachment in and around Li2CO3 particles was observed at longer times. The detachment was assumed to be part of a channel network within clusters of particles. Internal stresses within the primer resulting from buildup of inhibitor dissolution product within the voids were modelled using finite element analysis. It was found that strains related to von Mises stresses were concentrated around the inorganic particles and developed preferentially within the plane of the primer beneath the topcoat with some indication of concentration towards the primer/metal interface. These stresses resulted from osmosis and swelling related to the voids. They were also attributed to the observed cracking of the binder at some locations. Leaching experiments showed that Li was released very rapidly from the primer. The leaching data was modelled using a power law where the mass released is proportional to tn where the n is an index that reflects the kinetic behavior dictated by the evolving primer porosity. In this study n values between 0 and 1 were observed for all species, with Li starting at around 0.7 but rapidly decreasing to close to zero.

While paint coatings act as important barriers to corrosion, defects can lead to localized, rapid metal loss. The addition of corrosion inhibitors that are capable of leaching from a coating to protect the metal surface at a defect can prevent this type of corrosion. This work investigates the release and corrosion protection capabilities of two rare earth (RE) carboxylate inhibitors from an epoxy coating as an initial step to understanding their leaching behavior and interaction with the coating system. Leaching experiments were performed via inductively coupled plasma mass spectroscopy (ICP-MS) analyses of the solutions in which free-standing coatings loaded with varying concentrations of inhibitor compounds had been immersed. Inhibitor release from the epoxy coating was observed to be dependent on initial inhibitor concentration, inhibitor chemistry, and solution pH conditions. The coating systems with greater initial inhibitor loadings showed higher leaching rates, particularly in acidic environments. Following immersion, the absence of characteristic inhibitor peaks in the FTIR spectra of the coatings also confirmed leaching had taken place. Cross-sectional views of the coatings after exposure to the pH 1 environment presented a chloride infusion zone at the coating/solution interface where the inhibitor had leached out. The RE active inhibition provided by the leached RE carboxylate inhibitors was verified by exposure of a coating defect to a chloride contaminated environment.

The erosion-corrosion behaviour of a near fully dense 316L stainless steel (316L SS), with relative density higher than 99.5%, produced by selective laser melting (SLM) has been evaluated, for the first time, in a jet impingement system. Although the SLM-produced 316L SS possessed superior pitting corrosion resistance and higher hardness, unexpectedly, it has shown lower erosion-corrosion resistance than its conventionally produced commercial counterpart. This behaviour has been related to weaker repassivation ability of the SLM-produced 316L SS mainly due to the presence of the SLM process-induced pores within the specimen.

In this work two novel rare-earth (RE) 3-(4-methylbenzoyl)-propanoate (mbp) complexes (RE(mbp)3; RE = La, Y) have been investigated and compared with the well-researched inhibitor, lanthanum 4-hydroxycinnamate (La(4-OHcin)3), for AS1020 mild steel in 0.01 M NaCl solutions. The electrochemical results reveal a high corrosion inhibition performance of Y(mbp)3 which is attributed to the build-up of a protective surface film with a high level of corrosion resistance particularly after 24 h. Surface analyses indicate that the metal surface is protected during the immersion in Y(mbp)3-inhibited solutions and the presence of Y is confirmed on the substrate surface.

Stable pits with H2 evolution preferentially occurred in an annular region surrounding the centre of AA2024 wire. The grain size and intermetallic particles (α-phase, Al7Cu2Fe, Al2CuMg, Mg2Si, Al2Cu) distributions were the same for both regions. However, the annulus had mixed orientations, high angle grain boundaries and microshear bands while the centre was dominated by [111] orientations and low angle grain boundaries with the latter being responsible for its passive nature.

Localized corrosion is usually resulted from nonuniform electrochemical and chemical processes occurring on metal surfaces at different spatial and temporal scales, frequently influenced by large scale environmental complexities such as stray currents and nano- or micro-scale heterogeneous metallurgical structures/defects such as porosities in materials. In order to predict the corrosion of large infrastructure such as buried pipelines and to develop alloys with superior corrosion resistance, it is necessary to probe and understand multi-scale electrochemical and chemical processes. Unfortunately conventional electrochemical and surface analytical techniques have difficulties in doing so due to the lack of either spatial or temporal resolution. This paper provides an overview of recent approaches to facilitating the probing of spatial and temporal scale localized corrosion processes by means of the combined used of advanced electrochemical and surface analytical techniques. Cases that the authors have firsthand experiences are briefly described to illustrate these applications.

An Al–Cu–Li aerospace alloy has been investigated to determine the order in which corrosion at different types of sites occurs in AA2099-T83. Specifically, the sequence of galvanic attack on intermetallic (IM) particles and other sites of AA2099-T83 was determined as a function of time, in 0.1 M NaCl, through the use of scanning electron microscopy and electron backscatter diffraction characterization techniques. The earliest attack occurred at isolated grains and grain boundaries and on Li-containing dispersoids. Similarly, some constituent IM particles showed evidence of trenching in the surrounding alloy matrix. These IM particles included Al7Cu2Fe and another group of unidentified particles which displayed complete trenching within the first 10 min of exposure. Al13(Fe, Mn)4 were next most active followed by Al37Fe12Cu2 with Al6(Fe,Mn) and large TiB2 particles being the least active.

Samples from the sphalerite-dominated zone of a seafloor massive sulfide chimney, the Satanic Mills Chimney of the PACMANUS hydrothermal field, have been investigated to determine the internal macrostructure and microstructure of this zone, the phases present, and the distribution of metals. A combination of electron probe microanalysis, electron backscattered diffraction, and x-ray diffraction has been used. At the macroscale, this zone of the chimney wall is heavily porous and is comprised primarily of sphalerite, enclosing minor chalcopyrite, pyrite, and wurtzite. A Pb–As sulfosalt layer of possible microbial origins is present at the outer edge of the sphalerite matrix, next to a pore. The sphalerite has grown in globules on the order of 300 μm in diameter. At the microscale, the sphalerite features a colloform texture and a duplex-type grain structure consisting of either fine-grain regions in the center surrounded by coarse-grained regions or radiating coarse grains only. Pb- and As-rich bands have been detected in the colloform sphalerite, and growth twins have been observed in both the sphalerite and chalcopyrite crystals. A qualitative description of the growth of a typical globule is given, including nucleation, crystal growth, and solute redistribution.

Electron and proton microprobes, along with electron backscatter diffraction (EBSD) analysis were used to study the microstructure of the contemporary Al–Cu–Li alloy AA2099-T8. In electron probe microanalysis, wavelength and energy dispersive X-ray spectrometry were used in parallel with soft X-ray emission spectroscopy (SXES) to characterize the microstructure of AA2099-T8. The electron microprobe was able to identify five unique compositions for constituent intermetallic (IM) particles containing combinations of Al, Cu, Fe, Mn, and Zn. A sixth IM type was found to be rich in Ti and B (suggesting TiB2), and a seventh IM type contained Si. EBSD patterns for the five constituent IM particles containing Al, Cu, Fe, Mn, and Zn indicated that they were isomorphous with four phases in the 2xxx series aluminium alloys including Al6(Fe, Mn), Al13(Fe, Mn)4 (two slightly different compositions), Al37Cu2Fe12 and Al7Cu2Fe. SXES revealed that Li was present in some constituent IM particles. Al SXES mapping revealed an Al-enriched (i.e., Cu, Li-depleted) zone in the grain boundary network. From the EBSD analysis, the kernel average misorientation map showed higher levels of localized misorientation in this region, suggesting greater deformation or stored energy. Proton-induced X-ray emission revealed banding of the TiB2 IM particles and Cu inter-band enrichment.

International audience; The corrosion behaviour of AA 1370 in different metallurgical states was studied in chloride-containing sulphatesolutions. The microstructures of a rod, a deformed strand and an annealed strand constitutive of wires wereexamined using scanning electron microscopy, transmission electron microscopy and electron backscattereddiffraction. Results offered evidence for the ultra-fine grain size, high density of interfaces and high level ofmisorientation of the interfaces as relevant explanations for the low corrosion resistance of the deformed strandcompared to the rod and the annealed strand.

The major applications of PGMs are as catalysts in automotive industry, petroleum refining, environmental (gas remediation), industrial chemical production (e.g., ammonia production, fine chemicals), electronics, and medical fields. As the next generation energy technologies for hydrogen production, such as electrolysers and fuel cells for stationary and transport applications, become mature, the demand for PGMs is expected to further increase. Reserves and annual production of Ru, Rh, Pd, Ir, and Pt have been determined and reported. Based on currently available resources, there is around 200 years lifetime based on current demand for all PGMs, apart from Pd, which may be closer to 100 years. Annual primary production of 190 t/a for Pt and 217 t/a for Pd, in combination with recycling of 65.4 t/a for Pt and 97.2 t/a for Pd, satisfies current demand. By far, the largest demand for PGMs is for all forms of catalysis, with the largest demand in auto catalysis. In fact, the biggest driver of demand and price for Pt, Pd, and Rh, in particular, is auto emission regulation, which has driven auto-catalyst design. Recovery of PGMs through recycling is generally good, but some catalytic processes, particularly auto-catalysis, result in significant dissipation. In the US, about 70% of the recycling stream from the end-of-life vehicles is a significant source of global secondary PGMs recovered from spent auto-catalyst. The significant use of PGMs in the large global auto industry is likely to continue, but the long-term transition towards electric vehicles will alter demand profiles.

Dealloying of S-phase particles on AA2024-T3 leave behind highly cathodic Cu-rich particles, creating a galvanic corrosion environment. Clustering of these particles intensify localised dissolution of adjacent matrix leading to pitting. Evaluation of such galvanic activities is critical to develop effective corrosion inhibitors. Unfortunately conventional electrochemical methods are unable to probe this type of anodic attack because in principle they only evaluate general corrosion and cannot measure galvanic corrosion currents flowing between particles and adjacent matrix. This work uses a multielectrode composed of four copper and forty-four aluminium electrodes to model galvanic activities occurring over a cluster of dealloyed S-phase particles to better understand localised attack and at clustered sites. The model Al-Cu multielectrode was shown to be an effective tool to investigate local interactions between Cu electrodes and Al electrodes which undergo significant anodic current densities, simulating the anodic attack on the aluminium matrix of AA2024-T3. Additionally this tool can more strictly differentiate between inhibitors for localised corrosion control. An environmentally friendly rare earth corrosion inhibitor, praseodymium mercaptoacetate (Pr(MAcet)3), has been evaluated by this technique and has been found to rapidly reduce anodic current densities at a faster rate than PrCl3 when concentrations were sufficiently high (>10-3 M).

High-strength aluminium alloys such as AA2024-T3 are often developed by the introduction of plastic deformation to a precipitate containing microstructure. These alloys contain complex, near-surface nanostructures whose effects on localised corrosion processes have not been well understood due primarily to the difficulty of characterising these heterogeneous compositions and structures. In this work, we observed entangled oxide networks co-located with dislocation structures piled up at corroded intermetallic particles of an AA2024-T3 alloy. It was revealed that dislocation arrays act as pathways for corrosive species and promote structural degradation at interfacial regions, providing a new insight into corrosion initiation at the nano-scale.

The role of constituent intermetallic particles in the pitting corrosion of aluminium (Al) alloys is well recognised. A definitive quantification of the role of unique constituent particles has contributed towards an enhanced understanding of Al-alloy corrosion, however the complexity of Al-alloy microstructures warrants further attention. In the present work we identify a unique intermetallic type in contemporary versions of AA2024-T3, which has a two-phase structure, defined by two distinct crystal types, and distinct compositions. Detailed characterisation is used to unambiguously define this constituent, along with its role in localised corrosion.

Studies of Li depletion in sections of a Li 2 CO 3 -primer comprising a polyurethane binder, MgO, TiO 2 , BaSO 4 in addition to Li 2 CO 3, were performed using a combination of particle induced γ-ray and X-ray emission spectroscopies along with SEM/EDS analysis. A mixture of depletion behaviours was observed. At the earliest stages (to around 48 h)initial release was confined to the surface. At longer times (168 h)voids developed deeper into the primer and after 500 h Li 2 CO 3 dissolution was observed at places throughout the thickness of the primer to the metal/primer interface. Microscopic transport pathways formed which involved all large inorganic particles. SEM showed that rupture of the polyurethane matrix contributed to network formation. Finite element analysis indicated that rupture may be due to internal stresses around particles isolated in the polyurethane matrix and associated with water uptake. Thus the transport network seemed to be generated by chemical dissolution at the particle/polymer interface and may be enhanced by mechanical degradation due to internal mechanical stresses. The release kinetics of the Li 2 CO 3 inhibitor from the primer was followed as a function of time and the data analysed according to a release behaviour of t n . There was very rapid initial release of Li followed by a slower release of Mg and to a lesser extent Ba. The value of n varied significant with time, but showed a mixture of Fickian release and direct dissolution for Mg and Ba at intermediate times, but transport through a pore network at longer times. The leaching data was interpreted in terms of local transport networks that developed in the primer with time.

Electrochemically integrated multi-electrode arrays are variously designed for probing complex localised corrosion initiation and propagation processes occurring over different spatial and temporal scales. Electrode arrays made of 100 μm and 1 mm diameter aluminium alloy AA2024-T3 wires were used to illustrate the probing of submillimetre and millimetre scale localised corrosion processes over heterogeneous metal surfaces, while a patterned electrode array was employed to probe co-operative corrosion occurring across different metallurgical and microstructural features. The combined use of variously designed and patterned electrode arrays and surface analytical techniques is shown to provide unique insights into different stages of localised corrosion on heterogeneous alloy surfaces.

Despite the obvious advantages of additive manufacturing (AM) in producing metallic parts, defect formation remains a challenge that deleteriously impacts some critical materials properties of AM parts. Here, through electron microscopy and X-ray computed tomography (X-ray CT), new insights are revealed about lack-of-fusion (LOF) pores; the most common defect reported for AM. We show that LOF pores are not simply a void but a complex structure comprising oxide films decorating pore walls and grain refined regions with dislocation structures surrounding the pore. The formation of a thin nanocrystalline metallic layer on the pore wall is also observed. Spatter particles are the source of most LOF structures at high densities typical of recommended processing conditions and can only be eliminated by careful selection of processing parameters. Data constrained modelling, which uses the materials’ properties, was used for generating 3D representations of the complex structure surrounding LOF pores from X-ray CT datasets.

Localised corrosion of 316 L stainless steel (316 L SS) produced by selective laser melting (SLM) was investigated by two and three-dimensional techniques. It was revealed that porosity, which inevitably exists in the SLM-produced parts, is a critical factor determining the susceptibility to localised corrosion. Specimens containing lack-of-fusion (LOF) pores were found to be extremely susceptible to localised corrosion, as indicated by their lower breakdown potentials measured in polarisation tests. Computed tomography (CT) analysis, capable of linking the microstructure and corrosion propagation paths in three dimensions, showed the development of localised corrosion at the sites of LOF pores upon exposure to ferric chloride solution.

The pitting corrosion resistance of 316L stainless steel (316L SS) additively manufactured by selective laser melting (SLM) has been reported to be substantially higher than its commercial counterpart due to the elimination of MnS inclusions. Here we report that the pitting corrosion resistance of the SLM-produced 316L SS declines drastically after thermal post-processing above 1000 °C. This unanticipated drastic decline in pitting resistance is explained based on the formation of deleterious MnS inclusions in the SLM-produced 316L SS after high-temperature thermal post-processing. This finding may have wide implications for determining suitable post-processing and industry application conditions for SLM-produced 316L SS.

The intergranular corrosion (IGC) resistance of 316L stainless steel (316L SS) produced by selective laser melting (SLM) was investigated using microscopy analysis and electrochemical measurements. The IGC resistance of SLM-produced 316L SS, determined using a double-loop electrochemical potentiokinetic reactivation test, was found to be substantially higher than that of conventional 316L SS. This unusual behaviour was explained by the fact that no Cr-rich precipitates were detected for SLM-produced specimens after long-term sensitisation heat-treatment and those SLM-produced specimens exhibited a high frequency of twin boundaries and low-angle grain boundaries along with fine grains, leading to the avoidance of localised Cr depletion.

Localized corrosion compromises the durability of high-strength aluminium alloys and challenges the value of these high-performance materials. Currently, the role of structures (especially nanostructures) that lead to localized corrosion initiation is not well understood due primarily to the difficulty of characterizing chemistry and structure at the atomic scales. Development of new alloys will add to the complexity arising from the emergence of heterogeneous structure/chemistry of new types of coarse intermetallic particles at the nanoscale. These complex structures might include inclusions containing residual deformation or small amounts of less considered elements, such as Mg or Li in particles consisting of Al, Cu, Fe, Mn, and Si elements. Besides, from nano- to even microscales, high-density structural features induced during deformation processes are prone sites of preferential attack. These aspects are interesting topics of ongoing research in alloy development and new applications should spur further investigations of their atomic-scale corrosion initiation.

With significant increases in the production and utility of magnesium (Mg) in the past decade, Mg-alloys remain an attractive material for weight reduction in several industries, 1 in addition to substantial exploration as electrode materials in primary and secondary batteries. 2‐3 In such cases, the unambiguous determination of factors that play a role in corrosion/electrochemistry of Mg are of critical importance. The influence of impurities on the corrosion of Mg has been well documented since the early 20 th century, 4 with tolerance limits for a number of elements in Mg proposed. 5 In particular, the influence of deliberate alloying additions of low levels of transition metals (iron, manganeseandzirconium)oncorrosionofMghavebeendocumented by systematic studies. 6 Furthermore, the comparison of the electrochemistry of pure Mg specimens with low (at commercial levels of ∼40 ppmw) and ultra low levels (≤ 1 ppmw) of Fe were also recently presented. 7 Such studies add to the evidence that impurity elements, nominally of low solubility, 8‐10 influence the corrosion electrochemistry of Mg. In spite of this, at least two key aspects with respect to the in-service performance of Mg remain under researched. The first of these includes the detection and analysis of impurity elements on the Mg surface, and the study of possible enrichment of impurity elements on Mg during dissolution; both aspects are worthy of elaboration. Regarding the analysis of impurity elements on Mg surfaces, this is a particularly challenging task for the common methods nominally used in corrosion related works. Nominally, impurity concentrations are in the parts per million range. For example, commercial purity Mg will nominally contain < 100 ppmw Fe, which is below < 0.01% on the basis of weight %, and even lower on the basis of atom %. The analysis of such low levels of Fe with accuracy is not readily possible by methods such as X-ray photoelectron spectroscopy or Auger electron spectroscopy, which require concentrations approaching 1% (which is ∼100 times larger than the typical Fe impurity content) for accurate detection. Similarly, the signal to noise ratio, and large interaction volume, from energy dispersive X-ray spectroscopy are also prohibitive. In fact, even imaging of, and evidence of, impurity Fe (which is known to be present from ICP analysis of chemically dissolved metals) using Field Emission Gun-Scanning Electron Microscopy (FEG-SEM) is elusive. Site-specific Transmission Elec

Localised corrosion is typical on AA2024-T3 due to intermetallic particles embedded in the alloy. The effect of intermetallic compositions on corrosion are not yet fully understood. EPMA data on AA2024-T3 surfaces before and after a 16. min immersion, analyses the influence of intermetallic clustering on the severity attack at local sites. While sites with a high number of domains and a large S-phase surface area typically lead to severe attack, maximising these features did not always lead to severe corrosion attack. Cerium or praseodymium mercaptoacetate inhibited corrosion ring formation. The common trends observed from such attack sites was also discussed.

De-alloying of S-phase in AA2024-T3 in the presence chlorides, is well-known. However, it is unclear how rare earth mercaptoacetate inhibitors affect this process when immersed in a 0.1. M NaCl solution. This paper analyses data obtained using EPMA on AA2024-T3 surfaces before and after a 16. min immersion period. Cerium and praseodymium mercaptoacetate inhibited the de-alloying process of S-phase particles. Although no significant change in composition was observed for cathodic intermetallics, each appeared to participate in local corrosion reactions as evidenced by the development of surface oxides. Clustering between S-phase and one of the Cu-containing intermetallic domains was also evident.

AA2024-Tx is one of the most common high-strength aluminium alloys used in the aerospace industry. This article reviews current understanding of the microstructure of sheet AA2024-T3 and chronicles the emergence of new compositions for constituent particles as well as reviews older literature to understand the source of the original compositions. The review goes on to summarise older and more recent studies on corrosion of AA2024-T3, drawing attention to areas of corrosion initiation and propagation. It pays particular attention to modern approaches to corrosion characterisation as obtained through microelectrochemical techniques and physicochemical characterisation, which provide statistical assessment of factors that contribute to corrosion of AA2024. These approaches are also relevant to other alloys.

Atom probe tomography (APT) has been used to investigate the surface and sub-surface microstructures of aluminum alloy 2024 (AA2024) in the T3 condition (solution heat treated, cold worked, and naturally aged to a substantially stable condition). This study revealed surface Cu enrichment on the alloy matrix, local chemical structure around a dispersoid Al20Mn3Cu2 particle including a Cu-rich particle and S-phase particle on its external surface. Moreover, there was a significant level of hydrogen within the dispersoid, indicating that it is a hydrogen sink. These observations of the nanoscale structure around the dispersoid particle have considerable implications for understanding both corrosion and hydrogen embrittlement in high-strength aluminum alloys.

Transport paths for inhibitor release within a model strontium chromate (SrCrO4) inhibited/epoxy primer have been studied using a combination of tomography techniques. It has been found that the SrCrO4 particles form independent clusters within the model primer. The clusters have a range of fractal dimensions with the largest clusters (a few hundred microns in size) having a fractal dimension of 2.36. Leaching of the SrCrO4 from the primer appears to be initially through direct dissolution of particles in contact with the electrolyte but changes to diffusion through void pathways created by dissolution of the SrCrO4 phase. No evidence was found for the diffusion of chromate ions through the epoxy. Transport through such clusters does not follow Fickian diffusion, which has traditionally been employed to describe inhibitor release dynamics. Release kinetics typically follow a tm behaviour where t is time and m is an index which would be 0.5 for Fickian diffusion. Thus the overall release with time will evolve, being initially the result of direct dissolution, then at intermediate times, be dominated by transport through the fractal network and at the final stage go to zero since all the strontium chromate will be dissolved from the cluster connected to the surface. Clusters not connected to the surface remain undissolved and form additional reservoirs for further release in when local damage occurs in their vicinity. This new model of inhibitor transport creates new strategies for the development of self-healing properties for coatings.

Lithium based inhibitors in aerospace coatings are seen as excellent replacements for their chromium counterparts which are both carcinogenic and heavier. However, Li is generally difficult to detect and following changes in its distribution due to corrosion is impossible with many standard techniques. Combining MeV Particle Induced Gamma and X-ray emission provides a powerful tool and in this paper we summarise some recent experiments on such coatings using the CSIRO Nuclear Microprobe. PIGE mapping of the LiCO3 particles and their patterning illustrates how the method will be extremely useful in monitoring surface corrosion.

Rare earths are used in the renewable energy technologies such as wind turbines, batteries, catalysts and electric cars. Current mining, processing and sustainability aspects have been described in this paper. Rare earth availability is undergoing a temporary decline due mainly to quotas being imposed by the Chinese government on export and action taken against illegal mining operations. The reduction in availability coupled with increasing demand has led to increased prices for rare earths. Although the prices have come down recently, this situation is likely to be volatile until material becomes available from new sources or formerly closed mines are reopened. Although the number of identified deposits in the world is close to a thousand, there are only a handful of actual operating mines. Prominent currently operating mines are Bayan Obo in China, Mountain Pass in the US and recently opened Mount Weld in Australia. The major contributor to the total greenhouse gas (GHG) footprint of rare earth processing is hydrochloric acid (ca. 38%), followed by steam use (32%) and electricity (12%). Life cycle based water and energy consumption is significantly higher compared with other metals.

The inhibitive effects of the dibutyl phosphate anion in cerium dibutylphosphate [Ce(dbp)3] on AA 2024-T351 immersed in 0·05M NaCl were evaluated by comparison with immersion in cerium chloride (CeCl3) in 0·05M NaCl as well as 0·05M NaCl alone. Scanning electron microscopy and energy dispersive X-ray hyperspectral mapping were used to examine the surfaces after exposure to the different inhibitor solutions. It was found that the dibutylphosphate anion produced additional inhibition for the matrix and the S phase intermetallic particles. The most significant mode of corrosion in the absence of inhibitors was in the form of rings of corrosion product. CeCl3 largely suppressed the formation of the rings of corrosion product, and the Ce(dbp)3 entirely eliminated them (for the time scales investigated here), indicating the additional inhibitive action of the dibutylphosphate anion.

The susceptibility of the aluminium alloy, AA2024-T3, to localised corrosion as well as the toxicity of chromate inhibitors are both well known facts. In this paper the effect on the corrosion of AA2024-T3 of the thiol-containing mercaptoacetate, when coupled with cerium or praseodymium is examined. Potentiodynamic polarisation and SEM/EDXS were used to analyse the inhibiting behaviour of the compounds cerium mercaptoacetate and praseodymium mercaptoacetate. Both inhibitors were predominantly cathodic inhibitors with increasing anodic inhibition after 24 h of immersion. A mechanism of film formation and corrosion protection was also proposed.

Progressive restrictions on the use of toxic chromate-based corrosion inhibitors present serious technical challenges. The most critical of these is the lack of non-toxic ‘green’ alternatives that offer comparable performance, particularly on corrosion-prone aluminium alloys such as the 2000 and 7000 series. In this study we used computational modelling methods to investigate the properties of a range of small organic, potentially safer inhibitors and their interactions with technologically relevant alloy surfaces. We have generated robust and predictive computational models of corrosion inhibition for a structurally related data set of organic compounds from the literature. Our studies have correlated molecular features of the inhibitor molecules with inhibition and identified those features that have the greatest impact on experimentally determined corrosion inhibition. This information can be used to drive guided decision making for in silico or experimental screening of molecules for their corrosion inhibition efficiency, while considering more carefully their environmental consequences.