Examinando por Autor "Bedmar, Javier"

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Comparison of Different Additive Manufacturing Methods for 316L Stainless Steel
(MDPI, 2021-10-29) Bedmar, Javier; Riquelme, Ainhoa; Rodrigo, Pilar; Torres, Belén; Rams, Joaquín
In additive manufacturing (AM), the technology and processing parameters are key elements that determine the characteristics of samples for a given material. To distinguish the effects of these variables, we used the same AISI 316L stainless steel powder with different AM techniques. The techniques used are the most relevant ones in the AM of metals, i.e., direct laser deposition (DLD) with a high-power diode laser and selective laser melting (SLM) using a fiber laser and a novel CO2 laser, a novel technique that has not yet been reported with this material. The microstructure of all samples showed austenitic and ferritic phases, which were coarser with the DLD technique than for the two SLM ones. The hardness of the fiber laser SLM samples was the greatest, but its bending strength was lower. In SLM with CO2 laser pieces, the porosity and lack of melting reduced the fracture strain, but the strength was greater than in the fiber laser SLM samples under certain build-up strategies. Specimens manufactured using DLD showed a higher fracture strain than the rest, while maintaining high strength values. In all the cases, crack surfaces were observed and the fracture mechanisms were determined. The processing conditions were compared using a normalized parameters methodology, which has also been used to explain the observed microstructures.
Effects of the heat treatment on the microstructure and corrosion behavior of 316 L stainless steel manufactured by Laser Powder Bed Fusion
(Elsevier, 2022) Bedmar, Javier; García-Rodríguez, Sonia; Roldán, M.; Torres, Belén; Rams, Joaquín
Additively manufactured AISI 316 L stainless steel samples were heat treated at temperatures from 400 ◦C to 1100 ◦C, and the corrosion behavior in chloride environments was electrochemically studied. Heat treatments at 400 ◦C and 650 ◦C increased the grain size and the treatment at 1100 ◦C formed MnCr2O4 inclusions. Also, these postprocessing techniques reduce the hardness and increased the porosity. Heat treatment at 400 ◦C increased the polarization resistance and maintained the pitting corrosion mechanisms of the additively manufactured samples. Heat treatments at higher temperatures reduced the polarization resistance but changed the corrosion resistance mechanisms.
Influence of the surface state on the corrosion behavior of the 316 L stainless steel manufactured by laser powder bed fusion
(Elsevier, 2022) Bedmar, Javier; Abu-Warda, Najib; García Rodríguez, Sonia; Torres, Belén; Rams, Joaquín
The effect of surface roughness on the corrosion behavior of 316 L stainless steel manufactured by LPBF has been evaluated. The behavior of the steel in the as-built state was compared to that ground up to 2500 grade. Three different aggressive environments were used: 3.5 wt% NaCl water solution, 3 wt% H2SO4 solution, and hightemperature oxidation at 800 ºC. The ground specimens showed higher corrosion resistance. The corrosion resistance was much smaller in the as-built samples for electrochemical tests, and the lowest mass gain after hightemperature oxidation was found in the ground specimens.
Manufacturing of Aluminum Matrix Composites Reinforced with Carbon Fiber Fabrics by High Pressure Die Casting
(MDPI, 2022-05-09) Bedmar, Javier; Torres, Belén; Rams, Joaquín
Aluminum matrix composites reinforced with carbon fiber have been manufactured for the first time by infiltrating an A413 aluminum alloy in carbon fiber woven using high-pressure die casting (HPDC). Composites were manufactured with unidirectional carbon fibers and with 2 2 twill carbon wovens. The HPDC allowed full wetting of the carbon fibers and the infiltration of the aluminum alloy in the fibers meshes using aluminum at 680 C. There was no discontinuity at the carbon fiber-matrix interface, and porosity was kept below 0.1%. There was no degradation of the carbon fibers by their reaction with molten aluminum, and a refinement of the microstructure in the vicinity of the carbon fibers was observed due to the heat dissipation effect of the carbon fiber during manufacturing. The mechanical properties of the composite materials showed a 10% increase in Young’s modulus, a 10% increase in yield strength, and a 25% increase in tensile strength, which are caused by the load transfer from the alloy to the carbon fibers. There was also a 70% increase in elongation for the unidirectionally reinforced samples because of the finer microstructure and the load transfer to the fibers, allowing the formation of larger voids in the matrix before breaking. The comparison with different mechanical models proves that there was an effective load transference from the matrix to the fibers.
Teaching Design, Arts, and Fashion Students about Plastics and Recycling: The Use of Online and Offline Escape Room Scenarios
(ACS, 2024-03-06) Vázquez-López, Antonio; Artigas-Arnaudas, Joaquín; Bedmar, Javier
Herein we propose the implementation of an “escape room” activity to reinforce chemistry-related concepts for students of the Bachelor of Arts and Fashion. In this work, a combined online and offline activity is developed, easily adaptable to different environments. The online activity consists of 5 blocks of multiple-quiz questions regarding the concepts taught in theory classes of the subject ranging from the basic concepts of densities of fluids to thermoplastics alongside other concepts such as recycling. After successfully completing each question block, one clue is revealed. The offline activity consists of 6 laboratory-based experiments based on the same concepts but providing an immersive scenario by the use of experiments and puzzles. The experiments are simple and related to concepts (polymer science, density, and recycling) for nonscientific bachelor’s degrees. The final objective is to obtain a four-digit code which can deactivate a “bomb” which is constructed with a simple Arduino microcontroller, providing a real urgency scenario for the activity. To construct the Arduino-based “bomb” minimum electronic parts and cost are needed as well as minimal programming knowledge, making this activity accessible to every teacher worldwide. An alternative to the use of Arduino by employing Google Collab is also provided. Positive feedback regarding concept consolidation and amusement has been observed.