Additive Manufacturing Processes in Selected Corrosion Resistant Materials: A State of Knowledge Review.

Additive manufacturing is an important and promising process of manufacturing due to its increasing demand in all industrial sectors, with special relevance in those related to metallic components since it permits the lightening of structures, producing complex geometries with a minimum waste of material. There are different techniques involved in additive manufacturing that must be carefully selected according to the chemical composition of the material and the final requirements. There is a large amount of research devoted to the technical development and the mechanical properties of the final components; however, not much attention has been paid yet to the corrosion behaviour in different service conditions. The aim of this paper is to deeply analyze the interaction between the chemical composition of different metallic alloys, the additive manufacturing processing, and their corrosion behaviour, determining the effects of the main microstructural features and defects associated with these specific processes, such as grain size, segregation, and porosity, among others. The corrosion resistance of the most-used systems obtained by additive manufacturing (AM) such as aluminum alloys, titanium alloys, and duplex stainless steels is analyzed to provide knowledge that can be a platform to create new ideas for materials manufacturing. Some conclusions and future guidelines for establishing good practices related to corrosion tests are proposed.

Removal of dyes, oils, alcohols, heavy metals and microplastics from water with superhydrophobic materials.

A wide variety of pollutants can be currently found in water that are extremely difficult to remove due to their chemical composition and properties. A lot of effort has been made to tackle this issue that directly affects the environment. In this scenario, superhydrophobic surfaces, which have a water contact angle >150°, have emerged as an innovative technology that could be applied in different ways. Their environmental applications show promise in removing emerging pollutants from water. While the number of publications on superhydrophobic materials has remained largely unchanged since 2019, the number of articles on the environmental applications of superhydrophobic surfaces is still rising, corroborating the interest in this area. Herein, we briefly present the basis of superhydrophobicity and show the different materials that have been used to remove pollutants from water. We have identified five types of emerging pollutants that are efficiently removed by superhydrophobic materials: oils, microplastics, dyes, heavy metals, and ethanol. Finally, the future challenges of these applications are also discussed, considering the state of the art of the environmental applications of superhydrophobic materials.

Superhydrophobic 304 Stainless Steel Mesh for the Removal of High-Density Polyethylene Microplastics.

Microplastics are a global issue that affects the environment, economy, as well as human health. Herein, we present a superhydrophobic 304 stainless steel mesh obtained by chemical etching followed by a liquid-phase deposition of lauric acid that can be used for microplastic removal. Field emission scanning electron microscopy (FE-SEM) and high-resolution X-ray photoelectron spectroscopy (HR-XPS), among other techniques, were used to identify the hierarchical structure and chemical composition of the surface. They revealed that iron laurate decreased the surface free energy. The 304 stainless steel mesh was superhydrophobic (169°) and superoleophilic (0°). Taking advantage of these wetting properties, we showed an innovative use of these superhydrophobic surfaces in the removal of microplastics. Additionally, we analyzed the removal efficiency from a surface and colloidal point of view that allowed us to explain and clarify why microplastics can also be removed by their wetting properties. The loss of a double electrostatic cloud between the microplastics and the predominance of van der Waals interactions in the organic phase promote the removal of these persistent pollutants from water.

Study of the Thermochemical Surface Treatment Effect on the Phase Precipitation and Degradation Behaviour of DSS and SDSS.

In this study, the effect of a plasma ion carburizing process to duplex and superduplex stainless steels (DSS and SDSS), at 925 °C for a long time, as thermochemical process influencing the microstructural evolution is presented. The objective is to analyse the diffusion elements' influence on the precipitation of secondary phases after additional short thermal treatment. A comparison among the different treatments was performed after the resulting microstructures were analysed by Field Emission-Scanning Electron Microscope. Precipitation of secondary phases-sigma (σ), chi (χ), nitrides and carbides-seemed to occur during the treatments in a similar way for both steels (DSS and SDSS), although they showed a different morphology and precipitation mode. General corrosion behaviour of untreated and treated samples was investigated by potentiodynamic tests in order to prove their corrosion resistance. It was found that an improvement of the surface protection after the plasma carburizing process occurred.