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A recently published study of high temperature nitridation of iron chromium aluminum alloys (FeCrAl) at 900°C in N2–H2 has redundantly shown the formation of locally confined corrosion pockets reaching several microns into the alloy. These nitrided pockets form underneath chromia islands laterally surrounded by the otherwise protective alumina scale. Chromia renders a nitrogen‐permeable defect under the given conditions and the presence of aluminum in the alloy. In light of these findings on FeCrAl, a focused ion beam–scanning electron microscope tomography study has been undertaken on an equally nitrided FeNiCrAl sample to characterize its nitridation corrosion features chemically and morphologically. The alloy is strengthened by a high number of chromium carbide precipitates, which are also preferential chromia formation sites. Besides the confirmation of the complete encapsulation of the corrosion pocket from the alloy by a closed and dense aluminum nitride rim, very large voids have been found in the said pockets. Furthermore, metallic particles comprising nickel and iron are deposited on top of the outer oxide scale above such void regions.
Using additive manufacturing to process precipitation-strengthened high conductive copper alloys
(2024)
The present study demonstrates a proof of principle for additive manufacturing of CuCr1Zr with alumina nanoparticles for precipitation strengthening via in-situ alloying, aimed at improving the alloy’s strength and conductivity through oxide dispersion strengthening. Gas-atomized CuCr1Zr powder was mixed with single-core and multi-core particles, produced by copper plating onto alumina nanoparticles. Furthermore, the study also investigated the effects of two functionalization ratios (1:1 and 1:10) for the single-core particles, as well as the use of different laser sources (red and green) in laser-based powder bed fusion (PBF-LB/M). Key results showed that multi-core particles exhibited poor miscibility, leading to highly inhomogeneous powder beds and defective samples with a high porosity. In contrast, single-core particles maintained spherical shapes and had minimal impact on the particle size distribution, making them suitable for in-situ alloying. The use of a green laser resulted in a relative density of up to 95%, while a red laser produced defect-free samples with relative densities exceeding 99.5%. However, microhardness measurements indicated no significant improvement due to the interaction with alumina nanoparticles.
Additive manufacturing of CuCr1Zr demonstrates significant potential for industrial applications, particularly in the field of e-mobility. This paper describes the process chain and key factors involved. Suitable raw material for laser-based powder bed fusion can be produced via close-coupled gas atomization. Using argon at a pressure of 0.8 MPa, spherical particles of up to 200 µm can be achieved. After sieving and air separation, a particle size distribution in the range from 20 µm to 60 µm was measured. Samples manufactured using a green qcw-laser exhibit a higher microhardness of 220 HV0.1 compared to conventional CuCr1Zr or samples produced with a red cw-laser. Based to the greater geometric flexibility of additive manufacturing, internal cooling inlets can be integrated into pin contacts, significantly reducing temperature increases during the application of charging currents up to 300 A. This effect is further enhanced by applying a silver coating to the contact. After water injection, no further temperature increase is observed.
The aim of the paper was to investigate the air oxidation behaviour of pack aluminised steels exposed at 650 °C for 1000 h in static natural air atmosphere. The pack coatings were doped by rare elements such as gadolinium (Gd), cerium oxide (CeO2), and lanthanum (La) in order to enhance the corrosion resistance and plasticity of the deposited layers. In this work, the following steels were used: 16M, T91, VM12, Super 304H, and finally SANICRO25. The results indicated a much higher corrosion resistance in the coated 16M, T91, and VM12 steels; the steels with a higher Cr content than 16 wt % Cr indicated a better behaviour in the uncoated state than in the coated state. However, the observed difference in mass gain between the uncoated and the coated austenitic steels was not enormous. Furthermore, the addition of RE elements to the coating showed some effect in terms of coating thicknesses and differences in the layer structures. The materials prior to testing and after the exposure were investigated using XRD, the SEM X-ray maps with an EDS instrument were used for particular samples to evaluate the phase identifications, element concentrations, microstructure, and chemical composition.
Due to the inhibiting behavior of Cu, NiCu alloys represent an interesting candidate in carburizing atmospheres. However, manufacturing by conventional casting is limited. It is important to know whether the corrosion behavior of conventionally and additively manufactured parts differ. Samples of binary NiCu alloys and Monel Alloy 400 were generated by laser powder bed fusion (LPBF) and exposed to a carburizing atmosphere (20 vol% CO–20% H2–1% H2O–8% CO2–51% Ar) at 620 °C and 18 bar for 960 h. Powders and printed samples were investigated using several analytic techniques such as EPMA, SEM, and roughness measurement. Grinding of the material after building (P1200 grit surface finish) generally reduced the metal dusting attack. Comparing the different compositions, a much lower attack was found in the case of the binary model alloys, whereas the technical Monel Alloy 400 showed a four orders of magnitude higher mass loss during exposure despite its Cu content of more than 30 wt%.