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.