Examinando por Autor "Merino-Millán, David"

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Hardness and Young's modulus evolution of low-power plasma sprayed Inconel 625 coatings exposed to high temperatures
(Elsevier, 2024-10-30) Merino-Millán, David; Garrido-Maneiro, Miguel Ángel; Múnez, Claudio J.; Poza, Pedro
The use of renewable energy sources has been increasing in recent years as it aims to balance the production of fossil fuels by 2050. Among the various alternatives, concentrated solar power plants are considered the most feasible due to their capability of storing energy. Ongoing research is conducted to enhance the performance of third-generation plants by achieving higher temperatures. It makes necessary to explore new materials. This research is focused on concentrated solar power plants with central tower receivers, for which coatings used nowadays do not withstand the new requirements. For this reason, an alternative plasma sprayed Inconel 625 coating has been proposed. This study confidently presents an analysis of the high temperature exposure effects on the coating's mechanical properties at two temperatures, 520 and 800 °C. The study focuses on the Young's modulus and hardness, and the results demonstrate a significant improvement in these properties due to the formation of secondary phases. Coating hardness increased gradually from 4.12 GPa to 5.3 GPa during exposition at 520 °C. In contrast, the increment was attained quickly during the first 24 h exposure at 800 °C, reaching 4.5 GPa, and then maintained for all times studied. The microstructure was characterized using transmission electron microscopy, which identified the presence of carbides and intermetallic phases. The application of these coatings will significantly enhance the performance of solar receivers due to their superior properties compared to the currently available Pyromark coatings
Metallisation of additive manufactured polyamide 12 by low pressure cold spray
(Elsevier, 2024-03-15) Verdi, Davide; Merino-Millán, David; Salazar, Alicia
Cold Spray is a solid deposition process that can expand the field of application of polymeric materials thanks to the build-up of a metallic coating that improves their electrical properties and the wear resistance, among others. The novelty of the Cold Spray deposition on polymers has as drawback the lack of processing models that allow to choose the manufacturing parameters and forecast the coatings and substrates properties. In this work, the influence of the processing parameters for Aluminium-Zinc coating build-up via Low Pressure Cold Spray on polyamide 12 additively manufactured via Fused Filament Fabrication was investigated. Several sets of processing parameters combinations were systematically modified to establish the deposition window, leading to a final set that allowed to determine the physical, microstructural, and mechanical properties of the coatings, and the physical and thermal properties of the polymeric substrate. For the fixed gas pressure of 0.45 MPa and gas temperature of 500 °C, the scanning speed and the powder mass flow rate had a strong influence. Thick coatings (around 850 μm in size) were achieved at high powder mass flow rate (26 g/min) at the expense of low bond strength (between 1 and 3 MPa). The surface roughness acquired the highest values in those samples where erosion took place, occurring this phenomenon at small standoff distances and low powder mass flow rate, and no finding any relationship with the transverse gun speed. The generation of an interface layer of mixed metallic particles polymeric substrate plays a key role in the subsequent metallic coating growth, with thicknesses that ranged from 30 μm to 200 μm. In the substrate, the crystallinity degree of the polyamide underneath the coating increased, evidence of a heat affected zone where temperatures around the crystallisation temperature were reached, that also promoted stretching of the polymeric substrate due to dilatational phenomena. All this accompanied of an overall decrease in the thickness of the PA12 coupon after coating build up deposition with the high powder mass flow rate. This evidence indicates that a large plastic deformation of the polymeric substrate at the most energetic combination of processing parameters took place