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Next-generation concentrated solar power (CSP) technology needs to work at high temperatures to increase its power generation efficiency. It represents overcoming some issues for the structural materials, such as corrosion mitigation. In the present work, the laser-surface texturing (LST) treatment is investigated as a surface modification method to mitigate corrosion of a duplex stainless steel for CSP structural material. Corrosion tests of duplex steel were carried out immersed in a static molten salt mixture of Li2CO3-Na2CO3-K2CO3 at 600 °C for 1000 h. Complementary microscopy, microanalysis and optical characterization techniques were used to analyse both the steel surface after LST and the oxide scales formed after corrosion tests. Results evidenced that the laser treatment favoured the formation of a denser oxide layer, improving its effectiveness as a protective barrier against further oxidation. Compared with an untreated surface, the laser-treated one significantly decreased the corrosion rate by 48 %., This research was funded by Direcció General d'Indústria and ACCIÓ (Generalitat de Catalunya) to IMEM-CIEFMA in the INNOTEC project with grant number ACE034/21/000031, and Agency for Administration of University and Research (Agència de Gestió d'Ajuts Universitaris i de Recerca, AGAUR) (2021 SGR 01053). Mohammad Rezayat also acknowledges the AGAUR Fellowship (FI-SDUR-2020) of the Generalitat de Catalunya for its financial support., Peer Reviewed, Postprint (author's final draft)

Molten carbonate salt nanofluids have become an excellent strategy to enhance the power generation efficiency of the next-generation concentrated solar power (CSP) technology due to their excellent thermophysical properties at high temperatures. The corrosion behaviour in contact with salt nanofluids is one of the main issues to address for implementing cost-effective steels as construction materials for CSP. In the present work, the effects of molten salt nanofluids with Al2O3 nanoparticles (<50 nm and 1.0 wt%) on the corrosion behaviour of AISI 301LN stainless steel have been investigated. Corrosion tests were carried out in a static molten salt mixture of Li2CO3–Na2CO3–K2CO3 at 600 °C for 1000 h. Complementary electron microscopy, microanalysis and optical characterization techniques and micromechanical tests were carried out to study the oxide scales formed after corrosion tests in salt nanofluids and base salt of reference. Results evidenced that doping nanoparticles in molten salts significantly decreased the corrosion rate by ~50%, compared with a base salt. Incorporating nanoparticles into the oxide scale, forming a nanostructure of reticulated Al2O3 nanoparticles generated a more homogeneous and dense oxide scale, increasing its hardness about 30% and enhancing its effectiveness as a protective barrier., Peer Reviewed, Postprint (author's final draft)

Laser surface texturing is a promising technique for improving the surface properties of metals. In this study, a nanosecond pulsed laser was used to perform surface texturing on a metastable austenitic stainless steel AISI 301LN. The effects of the number of laser passes (from 1 to 1000 passes) on the surface morphology, microstructure, and mechanical properties were investigated. The results show that the depth of laser tracks increases with the number of passes due to thermal accumulation. Increasing the number of laser passes produces a rougher surface, but beyond a certain value, a smoother texture is observed. The amount of a’-martensite phase induced by the laser increases with the number of passes, producing augments in hardness. However, again, this trend changes after a certain number of laser passes, and hardening saturates and even decreases. Therefore, selecting the appropriate laser processing parameters and number of passes is essential to control the dimensions of laser tracks and thus the desired surface texture and also to achieve the level of hardening., Peer Reviewed, Postprint (author's final draft)

Esta investigación analiza los efectos de un láser de pulsos de nanosegundos en las características del acero inoxidable AISI 301LN. El estudio pretende utilizar este material en una aplicación específica de almacenamiento de energía que incluye condiciones de alta temperatura y carga cíclica. El texturizado superficial con láser (LST) ha surgido como un tratamiento prometedor para mejorar las características de corrosión a altas temperaturas, y es el enfoque empleado en este proyecto. Tras el tratamiento, se examinaron la morfología, la rugosidad, la transición de fase, la microdureza y la tensión residual de la superficie en relación con la potencia del láser y la velocidad de escaneado. Para la caracterización se emplearon la microscopía electrónica de barrido (SEM), el análisis de rayos X, la dureza Vickers, la espectroscopía Raman, la espectroscopía infrarroja por transformada de Fourier (FTIR) y la difracción de electrones retrodispersados (EBSD). Los resultados revelaron que una alta potencia del láser y una baja velocidad de escaneado dan lugar a un mayor contenido de martensita, lo que se traduce en una superficie más dura y también la rugosidad aumenta significativamente, además de una mayor tensión residual. El aumento de la velocidad de escaneado o la reducción de la potencia del láser tienen el efecto contrario en las características. Tras las pruebas de corrosión, se han caracterizado por SEM las secciones transversales de las muestras. Se ha visto que las tasas de corrosión se pueden reducir por LST, alcanzando un 34% de reducción en el caso más relevante. Tras estos resultados, se investigó el compuesto de la capa de óxido mediante EBSD y difracción de rayos X (XRD) para comprender completamente el efecto de la LST. Por otra parte, las pruebas de fatiga muestran que cuando el LST afecta demasiado al estado de la superficie, la vida a fatiga del material puede reducirse en un 15%. Para explicar este efecto se utilizó la fractografía., La investigació analitza els efectes d'un làser polsat de nanosegons sobre el rendiment d'un acer inoxidable AISI 301LN. L'estudi pretén utilitzar aquest material en una aplicació específica d'emmagatzematge d'energia que inclou condicions d'alta temperatura i càrrega cíclica. La texturització de la superfície amb làser (LST) ha sorgit com un tractament prometedor per millorar les característiques de corrosió a altes temperatures, i és l'enfocament emprat en aquest projecte. Després del tractament, es van examinar la morfologia, la rugositat, la transició de fase, la microduresa i la tensió residual de la superfície en relació amb la potència del làser i la velocitat d'escaneig. Per a la caracterització es va utilitzar la microscòpia electrònica d'escaneig (SEM), l'anàlisi de raigs X, la duresa Vickers, l'espectroscòpia Raman, l'espectroscòpia d'infrarojos de transformada de Fourier (FTIR) i la difracció d'electrons retrodispersats (EBSD). Els resultats van revelar que l'alta potència del làser i la baixa velocitat d'escaneig donen lloc a un contingut de martensita més gran, que condueix a una superfície més dura, amb un augment significatiu de la rugositat i tensions residuals més altes. L'augment de la velocitat d'escaneig o la reducció de la potència del làser tenen l'efecte contrari sobre aquestes característiques. S'han fet proves de corrosió i les observacions amb SEM de la secció transversal de les mostres va demostrar que les taxes de corrosió es poden reduir per LST fins a un 34% en el cas més rellevant. Després d'aquests resultats, es va investigar la composició de la capa d'òxid mitjançant EBSD i difracció de raigs X (XRD) per entendre completament l'efecte de la LST. D'altra banda, les proves de fatiga mostren que el LST afecta negativament l'estat de la superfície i, aleshores, la vida a fatiga es redueix al voltant d'un 15%. Per explicar aquest efecte, es van fer estudis fractogràfics., The research looks into the effects of a nanosecond pulse laser on the performance of an AISI 301LN stainless steel. The study intends to use this material in a specific application of energy storage that includes high temperature and cyclic load conditions. Laser surface texturing (LST) has emerged as a promising treatment for improving corrosion characteristics at high temperatures, and this is the approach employed in this project. Following laser treatment, characteristics such as the morphology, roughness, phase transition, microhardness, and residual stress of the surface, were examined in relation to the main laser parameters, i.e., power and scanning speed. Scanning electron microscopy (SEM), X-ray analysis, Vickers hardness, Raman spectroscopy, Fourier transform infrared spectroscopy (FTIR), and electron backscatter diffraction (EBSD), were employed for characterisation. They revealed that high laser power and low scanning speed result in a larger martensite content, which leads to a harder surface, with a significant roughness increase, and higher residual stresses. Increasing scanning speed or reducing laser power have the opposite effect on those characteristics. Corrosion tests have been done and SEM of the cross-sectional samples showed that corrosion rates can be reduced by LST up to 34% in the most relevant case. Following these results, the composition of the oxide scale was investigated by EBSD and X-ray diffraction (XRD) to completely understand the effect of the LST. On the other hand, fatigue testing shows that LST impacts negatively on the state of the surface, and then fatigue life is reduced by around 15%. To explain this effect, fractographic studies were carried out., Incoming

The development of direct dimethyl ether (DME) solid oxide fuel cells (SOFCs) has several drawbacks, due to the low catalytic activity and carbon deposition of conventional Ni–zirconia-based anodes. In the present study, the insertion of 2.0 wt.% Ru-Ce0.7Zr0.3O2-d (ruthenium–zirconium-doped ceria, Ru-CZO) as an anode catalyst layer (ACL) is proposed to be a promising solution. For this purpose, the CZO powder was prepared by the sol–gel synthesis method, and subsequently, nanoparticles of Ru (1.0–2.0 wt.%) were synthesized by the impregnation method and calcination. The catalyst powder was characterized by BET-specific surface area, X-ray diffraction (XRD), field emission scanning electron microscopy with an energy-dispersive spectroscopy detector (FESEM-EDS), and transmission electron microscopy (TEM) techniques. Afterward, the catalytic activity of Ru-CZO catalyst was studied using DME partial oxidation. Finally, button anode-supported SOFCs with Ru-CZO ACL were prepared, depositing Ru-CZO onto the anode support and using an annealing process. The effect of ACL on the electrochemical performance of cells was investigated under a DME and air mixture at 750 °C. The results showed a high dispersion of Ru in the CZO solid solution, which provided a complete DME conversion and high yields of H2 and CO at 750 °C. As a result, 2.0 wt.% Ru-CZO ACL enhanced the cell performance by more than 20% at 750 °C. The post-test analysis of cells with ACL proved a remarkable resistance of Ru-CZO ACL to carbon deposition compared to the reference cell, evidencing the potential application of Ru-CZO as a catalyst as well as an ACL for direct DME SOFCs., This research has received funding from grant PID2021-126614OB-I00 funded by MCIN/AEI/10.13039/501100011033, Agencia Estatal de Investigación, Ministerio de Ciencia e Innovación, and AGAUR, Agency for Administration of University and Research (Agència de Gestió d’Ajuts Universitaris i de Recerca) (2021 SGR 01053). Mohammad Rezayat also acknowledges the AGAUR Fellowship (FI-SDUR-2020) of the Generalitat de Catalunya for its financial support. Miguel Morales Comas is Serra Húnter Lecturer Professor, and he is grateful to the Serra Húnter program (Generalitat de Catalunya)., Peer Reviewed, Postprint (published version)

This article discusses recent advancements in the Laser Surface Transformation Hardening (LSTH) process applied to industrial metals. It focuses on examining the microstructure of the metal surface layer and explores different methods of performing LSTH to evaluate mechanical and surface properties. The study also investigates the utilization of various industrial lasers and simulation software for the LSTH process. The careful analysis of heat transfer and temperature control during LSTH aims to prevent the generation of surface defects like micro-cracks and surface melting. Finite element method (FEM) software effectively simulates the LSTH process. The research provides a comprehensive overview of recent developments in LSTH, categorized based on different metals and subsequent testing, highlighting its applications in the automotive industry. Electrochemical, wear, and microhardness tests are investigated to assess the potential applications of automotive metals., Peer Reviewed, Postprint (published version)

En aquest treball de final de carrera, es vol realitzar un tractament de texturitzat superficial amb làser polsat de nanosegons a l'acer austenític metaesble AISI 301LN. A diferència d'altres texturitzats superficials amb làser, en aquest treball es fa servir la tècnica de texturitzat superficial làser oscil·latori. Amb aquest mètode s'aconsegueixen patrons circulars sobre les mostres. En aquest projecte s'han estudiat dues variables que poden afectar els diferents texturitzats, com l'amplitud i la freqüència d'oscil·lació del làser. Amb això, es pretén aconseguir saber quines són les variables i/o patrons que proporcionen millors propietats finals al material. Per poder comprovar els diferents canvis i conèixer les propietats finals del material, es fan anàlisis superficials per conèixer com afecta la rugositat superficial i la tribologia. També es realitzen assajos d'humectabilitat, de corrosió, de microduresa a la secció transversal i determinació de la microestructura i composició final després del texturitzat. Tot això, es compara per a cada textura diferent amb les mostres sense tractar per poder determinar quines són les millors variables i patrons oscil·latoris. L'obtenció de les diferents propietats mecàniques del material es fan amb l'ajuda de diferents màquines avançades de caracterització com és un microscopi SEM, el sistema FIB, microduròmetre, microscòpia confocal, etc., En este trabajo de final de carrera se ha realizado un tratamiento de texturizado superficial con láser pulsado de nanosegundos en el acero inoxidable austenítico metaesble AISI 301LN. A diferencia de otros texturizados superficiales con láser, la novedad de este estudio reside en que se ha utilizado la técnica de texturizado superficial mediante láser oscilatorio. Con este método se consiguen patrones circulares sobre las muestras. En este proyecto se han estudiado dos variables que pueden afectar a los diferentes texturizados, como son la amplitud y la frecuencia de oscilación del láser. Con ello, se pretende conseguir saber cuáles son las variables y/o patrones que proporcionan mejores propiedades finales al material. Para poder comprobar los diferentes cambios y conocer las propiedades finales del material, se realizan análisis superficiales para determinar cómo se modifica la rugosidad superficial. También se realizan ensayos de humectabilidad, de corrosión, de microdureza en la sección transversal y se determinan de la microestructura y la composición final después del texturizado. Todo ello; se compara para cada diferente texturizado con las muestras sin tratar para poder determinar cuáles son las mejores variables y patrones oscilatorios. La determinación de las diferentes propiedades, se ha realizado con la ayuda de diferentes equipamientos avanzados de caracterización como un microscopio SEM, el sistema FIB, microdurómetro, microscopia confocal, etc., In this final project, we want to carry out a surface texturing treatment with a nanosecond pulsed laser on the AISI 301LN metastable austenitic steel. Unlike other laser surface texturing, the oscillatory laser surface texturing technique is used in this work. With this method, circular patterns are achieved on the samples. In this project, two variables have been studied that can affect the different texturing, such as the amplitude and frequency of oscillation of the laser. With this, it is intended to get to know which are the variables and/or patterns that provide better final properties to the material. In order to verify the different changes and find out the final properties of the material, surface analyzes are carried out to find out how it affects the surface roughness and tribology. Wettability, corrosion, microhardness tests are also carried out in the cross section and determination of the microstructure and final composition after texturing. All this is compared for each different texturing with the untreated samples in order to determine which are the best variables and oscillatory patterns. The different mechanical properties of the material are obtained with the help of different advanced characterization machines such as a SEM microscope, the FIB system, microdurometer, confocal microscopy, etc.

Laser cutting is a widely used manufacturing process, and the quality of the resulting cuts plays a crucial role in its success. This research employed the Design of Experiments (DOE) to investigate the impact of input process parameters on kerf quality during the laser cutting of 5 mm polymethyl methacrylate (PMMA) sheets. Response surface methodology (RSM) was utilized to model the relationship between the input parameters and the kerf quality, with regression equations developed for each response using the Design Expert software. A statistical analysis revealed the significant effects of high laser power, cutting speed, and focal plane position on kerf quality. Optimization, guided by the desirability function, identified optimal parameter combinations that offered the most favorable tradeoff among various responses. Optimal conditions were found to involve a high laser power, a cutting speed ranging from 4 to 7 mm/s, and a focal plane position at the center. Experiments indicated the suitability of the models for practical applications. An overlay plot analysis revealed a weak negative correlation between the laser power and the cutting speed, while the focal plane’s position could be adjusted independently., M. Rezayat acknowledges the AGAUR Fellowship (FI-SDUR-2020) of the Generalitat de Catalunya for its financial support., Peer Reviewed, Postprint (published version)