Due to the limited wear and corrosion properties of the austenitic tainless steel AISI 316 L, some applications require the benefits of nitriding. The aim of this work was to investigate whether the same positive effect of nitriding could be obtained for 316 L that was additive manufactured using the laser powder-bed fusion process and further solution treated at 1060 °C for 30 min, low-temperature plasma nitrided at 430 °C or both. This study was designed to better understand the additive-manufactured and solution-treated microstructures as well as developing a nitride and a diffusion layer. The comparison of the wear and corrosion resistance, the microhardness and the microstructure changes of the additive-manufactured steel in different post-treated conditions with a commercial steel was carried out. It was found that the post-treated low-temperature plasma nitriding improves the wear and corrosion resistance of the additive-manufactured samples. The obtained values are similar to the values of conventionally fabricated and nitrided 316 L. The solution treating itself (without further nitriding) did not have any significant impact on these properties. It was possible to explain the microstructure at the nano level as well as correlating the wear and corrosion properties.
COBISS.SI-ID: 1528746
We present a detailed analysis of the hybrid fabrication of test parts made from Inconel 718 using two additivemanufacturing (AM) technologies: selective laser melting (SLM) and directed-energy deposition (DED). This combination should allow the manufacturing of larger parts with geometrically complex structures that no other technologies could achieve. However, it is necessary to ensure the consistency of the mechanical properties of such parts. The hybrid SLM/DED parts, as well as the individual SLM and DED processed parts, were evaluated in terms of microstructures and mechanical properties, to understand the mechanisms that control the properties. We introduced a custom solution treatment and aging to dissolve the Laves phase, which was present in the DED part, where it reduced the mechanical properties. For a hybrid part with excellent properties, there must be good bonding between the SLM and DED parts, while the DED process must be adapted to prevent ?-phase precipitation. This new technology has the potential to produce high-added-value metallic products for space applications, that benefit from the properties developed through hybrid AM.
COBISS.SI-ID: 45252611
In this study we have assessed the microstructure details of 316L stainless steel produced by the additivemanufacturing selective-laser-melting technique under industrial conditions and correlated them with the mechanical properties. The employed micro- and nano-scale imaging electron microscopy techniques revealed the formation of a rigid hierarchical microstructure, which was driven by the rapidly changing solidification rates. The latter also affected the alloying atoms' distribution in the melt-pool boundary area as well as in the dislocation-dense regions. The melt-pool boundaries in themselves did not produce structural irregularities, but were shown to have a slightly different chemical composition. The arrangement of the complex dislocation cells that developed in the whole material volume led to an increase in the yield strength. The calculated twentytimes-higher dislocation density compared to that of the forged material was linked to a very low strength hardening. The similarity of the calculated yield strength, which came from the experimentally determined structure parameters, with the experimental value additionally supported the structure/mechanical properties correlation, derived in this work.
COBISS.SI-ID: 1529002
Samples of Nitinol were oxidized using different procedures in order to improve their biocompatibility and prevent the release of Ni. The evolution of the surface oxide films was monitored using Auger electron spectroscopy (AES). The only procedure that led to the formation of nickel-free oxide films involved a pre-treatment with hydrogen plasma for 10 s followed by a treatment with a plasma composed of 90% H2 and 10% O2. Optical emission spectroscopy revealed an extremely high dissociation fraction for both the hydrogen and oxygen molecules at a discharge power of 600 W, where the luminous plasma was concentrated in a volume of about 0.1 dm3. The extreme chemical reactivity of such a plasma resulted in the formation of an oxide film in about 15 s, meaning that external oxidation took place. The biocompatibility investigations, performed according to the ISO standard protocol using L929 cells, showed the absence of any cytotoxic effects that might be due to a contact between the biological materials and nickel. The investigation of nickel release of samples exposed to Hank’s solution, measured by ICP-OES showed negligible Ni concentrations.
COBISS.SI-ID: 21981974
18Ni-300 maraging steel manufactured by selective laser melting was plasma nitrided to improve its wear and corrosion resistance. The effects of a prior solution treatment, aging and the combination of both on the microstructure and the properties after nitriding were investigated. The results were compared with conventionally produced 18Ni-300 counterparts subjected to the same heat- and thermo-chemical treatments. The plasma nitriding was performed under the same conditions (temperature of 520 °C and time of 6 h) as the aging in order to investigate whether the nitriding and the aging could be carried out simultaneously in a single step. The aim of this work was to provide a better understanding of the morphology and chemical composition of the nitrided layer in the additive-manufactured maraging steel as a function of the prior heat treatments and to compare the wear and corrosion resistance with those of conventional maraging steel. The results show that nitriding without any prior aging leads to cracks in the compound layer, while nitriding of the prior-heat-treated additive-manufactured maraging steel leads to benefits from the thermochemical treatment in terms of wear and corrosion resistance. Some explanations for the origins of the cracks and pores in the nitride layers are provided.
COBISS.SI-ID: 50534915