With a volume fraction of austenite and ferrite that is roughly equal, duplex stainless steels (DSS) have good mechanical characteristics and a high level of corrosion resistance. On the other hand, for decades, laser welding of sheets has been adopted as a profitable technology for joining many metallic materials. Obtaining a balanced microstructure and ensuring its qualities and uses is the difficulty in DSS laser welding. Generally, when DSS is welded with a technique inherently associated with high cooling rates, a mostly ferritic microstructure results. The addition of austenite stabilizing elements or heat treatments is indicated to balance the microstructure. Before butt welding two UNS S32750 DSS sheets with a pulsed Nd:YAG laser, a 50-µm-thick cobalt layer was electro-deposited onto the edge of one of them with a Watts bath procedure. The microstructural characterization of the weld beads was performed using optical microscopy, scanning electron microscopy, energy dispersive spectroscopy, and X-ray diffraction. The volume fractions were determined using two methods: (1) Image analysis software for SEM images and (2) computerized volume fraction computation from XRD spectra. As the volume fractions of austenite increased, the results demonstrated that adding cobalt in the fusion zone effectively resolved the unwanted unbalanced microstructure that resulted from autogenous laser welding of the DSS. Residual stresses were determined for the austenitic phase and the ferrite matrix in the weld bead, the former resulting affected by tensile stresses, while the latter by compressive stresses.

In this work, antifouling copper-containing PEO coatings were produced on zinc-aluminized steels and their antifouling properties in circulating seawater were tested at the Hydrobiological Station Umberto D'Ancona located in Chioggia (Venice, Italy). The effect of the presence of the copper particles on the localized corrosion properties of the PEO coatings was also investigated in depth. In detail, the PEO-coated samples were produced and characterized in terms of microstructure and phase composition through SEM and XRD analysis. The antifouling properties of the samples were evaluated through stereo-microscope and SEM observations after up to 28 days of immersion and the corrosion properties were analyzed with EIS and SVET tests. The results, besides the successful incorporation of the copper particles into the coatings, evidenced the remarkable antifouling effect of the copper particles which also produced a clear selection in the type of algae that can colonize the samples. Considering the corrosion properties, the copper particles were found to be detrimental, due to the galvanic coupling with the substrate. Considering both results, the copper-containing PEO coating can be suggested only in combination with a topcoat which further increases the corrosion performance.

Plasma-activated water (PAW) is a recently developed cutting-edge technology that is increasingly gaining interest for its applications in medicine, food industry and agriculture. In plant biology, PAW has been shown to promote seed germination, plant growth, and plant resistance to biotic and abiotic stresses. Despite increasing knowledge of the beneficial effects exerted by PAW on plants, little information is currently available about how this emerging technology may affect the mutualistic plant-microbe interactions in the rhizosphere. In this work we have investigated the impact of irrigation with PAW, generated by a plasma torch, on arbuscular mycorrhizal (AM) symbiosis between the model legume Lotus japonicus and the AM fungus Rhizophagus irregularis . Since PAW sensing by plants has recently been demonstrated to occur through calcium-mediated signalling, we monitored early cellular responses to different doses of PAW in L. japonicus roots expressing the Ca2+ -sensitive photoprotein aequorin targeted to either the cytosol or nucleus. Quantitative analyses of AM fungal accommodation in host roots along with phosphate accumulation in leaves, as well as chemical analysis of N, C, S in shoots, showed that treatments with PAW play a modulatory role on plant AM symbiotic performance, in a manner dependent on the time interval of water exposure to the plasma and on the duration of plant irrigation treatment with PAW. Establishing a solid scientific ground for plasma-related technology may provide key elements to develop tools and treatments aimed to increase crop plant yield in a sustainable manner. ### Competing Interest Statement The authors have declared no competing interest.

In this work, the possibility of incorporating TiO2 titanium dioxide particles derived from the recycling process of photovoltaic panels into PEO coatings was investigated. These particles constitute the main filler of the polymer constituting the rear part of the panels, and are characterized by possessing photocatalytic properties. The particles were added in different quantities to the electrolyte (a basic solution containing sodium silicate). The incorporation into the PEO coating produced on an aluminum alloy 1050, and the possibility of conferring photocatalytic properties to the surface of the samples were studied. The different samples were first characterized by optical microscope analysis, SEM and XRD and from the point of view of corrosion resistance by means of potentiodynamic tests. The photocatalytic properties of the samples were evaluated by monitoring the degradation of aqueous solutions of methylene blue exposed to a UV lamp. The particles have been successfully incorporated into the coating, and their presence does not alter the corrosion properties, which are improved compared to the uncoated sample. The particles, initially composed of a mixture of rutile and anatase, are instead transformed into rutile after incorporation due to the locally very high temperatures that can occur during the PEO process. In the samples obtained with higher quantities of titanium dioxide particles (60 and 80 g/L), a significant photocatalytic effect is observed with a significant reduction of methylene blue.

Super-duplex stainless steel (SDSS) shows high mechanical and corrosion resistance because of the balanced structure of austenite and ferrite. However, maintaining this phase ratio after welding is a challenge. The use of austenite stabilizing components is recommended to balance the microstructure. The addition of alloying elements presents a challenge because of the characteristics of Nd:YAG pulsed laser welding. An approach, which has proven to be effective, is to use metal electroplating to prepare the surfaces of the mechanical SDSS components that will be welded, therefore promoting the phase balance in the fusion zone. While the effects of metals such as nickel as an austenite stabilizer are well recognized, cobalt’s effects require more research. The present work investigated the influence of the use of cobalt addition in the joining process by preliminary electroplating on UNS S32750 SDSS Nd: YAG pulsed laser welding, specifically regarding microstructure and microhardness. Three conditions were investigated, changing the thickness of the deposited cobalt layer. The addition of cobalt modified the morphology and increased the volume fraction of austenite. An austenite volume fraction of around 48% was obtained using a 35 μm thick cobalt coating. The microhardness was affected by austenite/ferrite proportions. The microhardness dropped from about 375 HV to 345 HV as the cobalt layer’s thickness rose, being similar to that of the base metal. The effect of cobalt as an austenite stabilizer was observed, and the cobalt electroplating technique was effective to correct the phase balance on UNS S32750 laser welding.

Several metallic materials are employed in the manufacture of solenoid valve for domestic heating systems. However, galvanic corrosion could be a problem when two different materials are electrically coupled to each other in the presence of electrolytes. To avoid this, several types of protective coating have been developed. In this work, the galvanic corrosion between brass (both chromate coated and un-coated) and three kinds of metals, AISI 430, galvanized steel and aluminum alloy (both passivated and un-passivated), were studied in aggressive solutions (3.5 % NaCl), using a potentiostat in zero resistance ammeter mode (ZRA). Further ZRA tests were conducted using an external potential of 0.7V DC.

Non-thermal plasma technology is increasingly being applied in the plant biology field. Despite the variety of beneficial effects of plasma-activated water (PAW) on plants, information about the mechanisms of PAW sensing by plants is still limited. In this study, in order to link PAW perception to the positive downstream responses of plants, transgenic Arabidopsis thaliana seedlings expressing the Ca2+-sensitive photoprotein aequorin in the cytosol were challenged with water activated by low-power non-thermal plasma generated by a dielectric barrier discharge (DBD) source. PAW sensing by plants resulted in the occurrence of cytosolic Ca2+ signals, whose kinetic parameters were found to strictly depend on the operational conditions of the plasma device and thus on the corresponding mixture of chemical species contained in the PAW. In particular, we highlighted the effect on the intracellular Ca2+ signals of low doses of DBD-PAW chemicals and also presented the effects of consecutive plant treatments. The results were discussed in terms of the possibility of using PAW-triggered Ca2+ signatures as benchmarks to accurately modulate the chemical composition of PAW in order to induce environmental stress resilience in plants, thus paving the way for further applications in agriculture.

Duplex stainless steels (DSS) are increasingly employed in the industry based on their combination of good mechanical properties and high corrosion resistance. These properties are achieved by stabilising quasi-equal volume fractions of the austenitic and ferritic phases at room temperature. The pitting resistance of a DSS is influenced by its chemical composition, presence of second phases, heat treatment, grain size, cold working, as-well-as surface roughness. In this research, LDX 2101 (EN 1.4162) lean DSS is investigated at different grades of cold deformation (thickness reduction from 9% to 61%), obtained by multi-pass cold rolling. The effect of this type of cold-working method on the corrosion properties of the material was evaluated by means of potentiodynamic polarization tests at room temperature in 3.5 wt.% NaCl solution and of critical pitting temperature (CPT) evaluation in 1 M NaCl solution. The results of the corrosion tests were also linked with proper OM and SEM microstructural observation and with results of XRD tests. The results showed that the multi-pass cold rolling does not affect the corrosion properties of the investigated material with deformation steps that are <10%. Corresponding to this finding, the microstructural and phase analysis investigations proved that no strain-induced martensite was formed during the process. The obtained results were also compared with single-pass cold-rolled properties of the material from a previous study pf the authors. As an effect of single-pass cold rolling, the same DSS (LDX2101) suffers a significant decrease of the CPT and destabilisation of the protective oxide layer with the thickness reduction. Therefore, this research shows that it is advisable to use multi-pass cold rolling instead of the single-pass method to reach high deformations without the deterioration of corrosion properties.

In this work, plasma electrolytic oxidation (PEO) process was used to produce bioactive coatings, mainly composed by hydroxyapatite (Hap) and titanium oxide, on grade 2 titanium alloy. All PEO treatments were carried out using a maximum voltage of 315 V, a lower value in comparison with the works present in literature, thus resulting a more environmentally friendly process. The effects on the PEO coatings of KOH addition to electrolyte and of working in direct or pulsed current mode, were also investigated. The morphology and elemental composition of the coatings were characterised by scanning electron microscopy (SEM), whereas the phase analysis was carried out with X-ray diffraction (XRD). The corrosion resistance properties were investigated by open circuit potential measuraments, potentiodynamic polarization (PDP), and electrochemical impedance spectroscopy (EIS) tests. Moreover, cell-adhesion biological tests were performed. SEM analysis evidenced the presence of needle-shape crystals of hydroxyapatite, as confirmed by XRD, that totally or partially filled the pores of PEO layer. The corrosion test showed an improvement in the corrosion behaviour of the PEO coated samples in comparison with the untreated sample. Cell-Adhesion biological tests evidenced excellent cytocompatibility of the coatings with human cells and an improvement in the cell adhesion in comparison with the untreated sample.

In this work, we investigated the possible incorporation of YAG (yttrium aluminum garnet)-Ce particles into plasma electrolytic oxidation (PEO) coatings on 1050AA (aluminum alloy) in order to endow the surface with photoluminescent properties. Different treatment times and current modes (direct or pulsed) were tested as PEO process parameters using as electrolyte a silicates-containing solution. The microstructure of the samples was characterized by SEM and XRD measurements, the corrosion properties were determined by EIS tests, whereas the photoluminescence was evaluated with a proper spectrometer. The concentration of the YAG-Ce particles incorporated in the PEO coating was strongly influenced by the current mode, and in particular, it was higher with pulsed current mode. A higher content of YAG-Ce particles results in a better corrosion resistance and photoluminescent effect. PEO process in pulsed unipolar mode using an electrolyte containing YAG-Ce particles resulted an effective way to produce samples of 1050AA with a surface characterized by photoluminescent properties.

A process for producing a black oxide coating on aluminum alloy was investigated in the present work. The blackening process is widely used in industrial applications, but it was not deeply studied for aluminum alloys. The aim of this work is to study the black coating obtained on AA6060 surfaces employing two different solutions, both containing potassium permanganate, copper nitrate and nitric acid. The first solution carried out the coloring treatment at 50 °C, whereas the second one was done at room temperature. Different immersion times were investigated. The morphology of the coating was investigated by means of optical and electron microscopy to evaluate the color of the layer and the presence of defects, porosities, and cracks. X-ray diffraction analysis was performed to evaluate the protective layer composition. The corrosion properties were studied with potentiodynamic polarization tests and electrochemical impedance spectroscopy tests. The results showed that the blackening process performed at room temperature, besides the clear advantages in term of costs and safety, obtained more uniform coatings with increased corrosion performance in comparison with the ones obtained at higher temperatures.

Super-duplex stainless steel (SDSS) exhibits an austenite-ferrite dual-phase structure, which promotes many benefits upon single-phase grades, such as high mechanical strength and corrosion resistance. Welding process results in an unbalanced microstructure, with large amount of ferrite, which compromise SDSS’s properties. This paper investigates the effect of using electrolytic nickel foils as an addition metal on UNS S32750 SDSS Nd:YAG pulsed laser welding, through the evaluation of the microstructure, hardness, tensile strength, and corrosion resistance of the weld bead. Six conditions were investigated: autogenous welding and with addition of nickel, varying the thickness of nickel foil added. Microstructural analysis reveals an increase in volume fraction of austenite for the conditions with addition of nickel. Using a 30 µm thick nickel foil, approximately equal amount of austenite and ferrite was obtained in the weld bead. The higher microhardness was obtained for the autogenous welding, 400 HV and decreased with the addition of nickel. The tensile strength decreased 4% in the experimental conditions with high nickel addition. The corrosion resistances were the same for all the conditions with addition on nickel, regardless of the nickel foil thickness added, but it compared to autogenous welding the CPT’s increased approximately 14 °C.

Cu-Ti alloys are one of the main candidates to act as a substitute for Cu-Be alloys due to their more environmentally friendly nature. Cu-Ti alloys are age hardenable alloys, and their treatments can modify their microstructure, causing the formation of various Cu-Ti intermetallic that can strongly influence both the mechanical and corrosion properties. In this work, the effect of homogenization heat treatment at 1173 K followed by aging at 723 K for different times (0–24 h) on the microstructure, corrosion and mechanical properties of Cu-4.5 wt.%Ti alloy was investigated. Moreover, the corrosion mechanism based on the different kinetics for the formation of the protective oxide layer was studied. The microstructure and phase analyses were analyzed with SEM and XRD. The mechanical properties were investigated by microhardness test, whereas the corrosion properties were studied by potentiodynamic anodic polarization and potentiostatic tests in artificial sweat. The results showed that the cast sample had the highest corrosion resistance, and the mechanical properties decrease with the homogenization treatment and increase after the combination of homogenization and aging. A corrosion mechanism correlated to the amount and type of intermetallic material was proposed.

New generations of green concretes are often consuming large amounts of industrial waste, as recycled or manufactured aggregates and alternative binders substituting ordinary Portland cement. Among the recycled materials that may be used in civil engineering works, construction and demolition waste (C&DW), fly ashes, slags and municipal solid waste incinerator bottom ashes (MSWI BA) are those most diffused, but at the same, they suffer due to a large variability of their properties. However, the market increasingly asks for new materials capable of adding some specific features to construction materials, and one of the most interesting is the pozzolanic activity. Hence, this work deals with an experimental study aimed at assessing the technical feasibility of using an industrial waste comprised largely of MSWI BA, with small quantities of C&DW and electric arc furnace slag (EAFS), in green cement-based mixtures (cement paste and mortars). The aim of the work is to achieve the goal of upcycling such waste and avoiding its disposal and landfilling. Particularly, the test methods for assessing the pozzolanic activity of this waste are discussed, analyzing the efficacy of indirect methods such as the strength activity index (SAI), the conductivity test and the efficiency factor (k), together with a direct method based on lime consumption.

Plasma Electrolytic Oxidation treatment (PEO) is of great interest due to its capability to produce a thick ceramic coating with a great adhesion and very high corrosion and wear resistance on metallic components. Mainly characteristics of these coatings are a high porosity in the outer part of the coating and the opportunity to incorporate into the coating particles coming from the electrolyte. The aim of this work was to realize on an aluminum substrate a PEO coating with an homogeneous distribution of phosphors (in the form of YAG:Ce particles) in order to ensure good thermal conductivity and photoluminescence. This is important in application as LED where it is required a big heat exchange. Moreover, it was evaluated the effect of pulsed current compared to direct current on particles distribution.

A novel high silicon austempered (AHS) steel has been studied in this work. The effect of different austenitizing temperatures, in full austenitic and biphasic regime, on the final microstructure was investigated. Specimens were austenitized at 780 °C, 830 °C, 850 °C and 900 °C for 30 min and held isothermally at 350 °C for 30 min. A second heat treatment route was performed which consisted of austenitizing at 900 °C for 30 min and austempering at 300 °C, 350 °C and 400 °C for 30 min. Scanning electron microscopy (SEM) and X-ray diffraction (XRD) have been used to evaluate the microstructural evolution. These techniques revealed that the microstructures were composed of carbide-free bainite, ferrite, martensite and retained austenite (RA) in different volume fractions (Vγ). An aqueous borate buffer solution with 0.3 M H3BO3 and 0.075 M Na2B4O7∂10H2O (pH = 8.4) was used for corrosion tests in order to evaluate the influence of the different volume fractions of retained austenite on the corrosion properties of the specimens. The results showed that when increasing the austenitization temperatures, the volume fractions of retained austenite reached a maximum value at 850 °C, and decrease at higher temperatures. The corrosion properties were investigated after 30 min and 24 h immersion by means of potentiodynamic polarization (after 30 min) and electrochemical impedance spectroscopy (after both 30 min and 24 h) tests. The corrosion resistance of the samples increased with increases in the volume fraction of retained austenite due to lower amounts of residual stresses.

Increasing evidence indicates that water activated by plasma discharge, termed as plasma-activated water (PAW), can promote plant growth and enhance plant defence responses. Nevertheless, the signalling pathways activated in plants in response to PAW are still largely unknown. In this work, we analysed the potential involvement of calcium as an intracellular messenger in the transduction of PAW by plants. To this aim, Arabidopsis thaliana (Arabidopsis) seedlings stably expressing the bioluminescent Ca2+ reporter aequorin in the cytosol were challenged with PAW generated by a plasma torch. Ca2+ measurement assays demonstrated the induction by PAW of rapid and sustained cytosolic Ca2+ elevations in Arabidopsis seedlings. The dynamics of the recorded Ca2+ signals were found to depend upon different parameters, such as the operational conditions of the torch, PAW storage, and dilution. The separate administration of nitrate, nitrite, and hydrogen peroxide at the same doses as those measured in the PAW did not trigger any detectable Ca2+ changes, suggesting that the unique mixture of different reactive chemical species contained in the PAW is responsible for the specific Ca2+ signatures. Unveiling the signalling mechanisms underlying plant perception of PAW may allow to finely tune its generation for applications in agriculture, with potential advantages in the perspective of a more sustainable agriculture.

Blackening process of steel is widely used in many industrial applications to create a protective layer against corrosion, environmental attack and to improve the aesthetic features. This study is focused on obtaining a black coating on a low carbon steel surface employing three different solution. In particular, two solution based on sodium nitrate and sodium hydroxide were used at boiling point, while the third based on selenous acid at ambient temperature. The samples were immersed for 5, 15 and 30 min in the boiling solutions, while for cold solution it was chosen 1 min of immersion time. The morphology of the protective layer were studied with stereo-microscope in order to evaluate the color, and Scanning Electron Microscope (SEM) to identify any defects in the surface, X-ray diffraction (XRD) was used to evaluate the composition of the protective layer. The corrosion resistance was measured performing potentiodynamic polarization tests and electrochemical impedance spectroscopy tests. The layer obtained with 15 min immersion time for the two boiling solutions is dense and adherent as shown by SEM analysis. For the other immersion times the layer was not uniform with porosities. Cold solution lead to a not homogenous layer reducing corrosion resistance.

Obtaining a balanced microstructure in the fusion zone on a super duplex stainless steel (SDSS) weld is a challenge. The present work reports the use of the Watts bath to correct the phase balance on laser-welded SDSS. Three different Watts bath times were used, and the microstructure of the weld bead was evaluated. The Watts bath was efficient to correct the undesirable unbalanced microstructure resulting from SDSS laser welding as the austenite percentage increased.