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• Laser-deposition technique was employed for the fabrication. • The influence of laser process parameters on the corrosion resistance was investigated. • The scanning speed had more influence on corrosion behaviour than the laser power. • The Ti-based HEAs was more resistant to corrosion than the Cu-based HEAs. Corrosion is a conservational occurrence that has a large economic impact on most metals and its alloys because it destroys and deteriorates most materials by an electrochemical process through the reaction of these materials with the environment. High Entropy Alloys in aerospace applications react with the environment in applications such as jet engines, especially at elevated temperatures. Thus, the capacity of high entropy alloys to resist corrosion must be investigated to expand the application of this advanced material in the aerospace industry. In this comparative study, AlCoCrFeNiCu and AlCoCrFeNiTi High Entropy Alloy samples were fabricated by Laser Additive Manufacturing, particularly direct energy deposition and the corrosion behaviour of both alloys were examined and compared. The influence of the laser processing parameters on the microstructure and corrosion responses of the high entropy alloys in 3.5 wt% NaCl solution was also investigated. The microstructural morphologies were examined using an X-ray diffraction system (XRD) and Scanning electron microscope (SEM) equipped with Energy Dispersion Spectroscopy (EDS). The results showed that the Scan speed had the most influence on the microstructure and corrosion behaviour of the alloys. There was a strong relationship between the phase structure of the alloys and their susceptibility to localized corrosion. Therefore, it has been proposed in this study that the phase distribution within the alloys also influences the corrosion behaviour of laser deposited high entropy alloys. [ABSTRACT FROM AUTHOR]

The chemically architectured alloys were proposed as a new concept of microstructure, with a multi-scale architecturation. They are composed of a solid-solution at the atomic scale, grain boundaries and composition gradients at the micronic scale and finally a 3D network of gradients at the mesoscale. Composition gradients are between two phases with the same crystalline structure but different compositions. As a first application of this concept, powders of pure Ni and CoCrFeMnNi high entropy alloy were successfully densified by Spark Plasma Sintering. Then the microstructure and mechanical properties were characterized by scanning electron microscope coupled with energy dispersive spectroscopy and electron backscattered diffraction, X-ray diffraction, nanoindentation and compression tests. The obtained chemically architectured alloys present a homogeneous distribution of the two phases with a 10 μm wide chemical gradient in between. By comparison with reference non architectured materials, the chemical architecturation induces a 35% increase of the yield strength. Thus the concept of chemically architectured metallic alloys and composition gradients was proven as very promising: processing of this complex microstructure is possible and it induces a significant mechanical strengthening. Image 1 • A mixture of CoCrFeMnNi and Ni powders was fully densified by spark plasma sintering. • A chemical gradient of around 10 μm was formed between HEA and Ni phases. • This material is called a chemically architectured alloy. • Mechanical strength is improved compared to an ideal mixture of Ni and CoCrFeMnNi. [ABSTRACT FROM AUTHOR]

In this work we analyse the formation of sigma phase in Al x CrFeCoNi (x = 0–1.5) alloys. In order to characterise the Al x CrFeCoNi system, we decided to investigate 5 additional samples corresponding to the individual phases of alloys for x = 1 and 1.5. They were annealed at 600–1000∘C for 24 h. For each of those five samples scanning electron microscope, SEM, XRD and Mössbauer measurements were performed. The SEM/BSE images allowed identify the number of different phases present in the samples and EDX method gave elemental composition of every phase. The XRD technique helped identify those phases, and thanks to Mössbauer spectroscopy we were able to determine the percentage of each of them. The SEM/EDX measurements also revealed spherical Al precipitations which can be clearly divided into two groups in respect of diameter distribution. The analysis of the Mössbauer spectra revealed magnetically split and a paramagnetic component for phases rich in Cr as well as for a phase rich in Al and Ni. We established that the sigma phase is formed in the phase rich in Cr, and has a secondary character. We also provide the degree of transformation to sigma phase for every sample. • Separate sample series of AlxFeCrCoNi HEA were fabricated, their properties were compared. • FeCrCoNi-rich fcc phase forms a doublet in Mössbauer spectrum. • σ phase transforms from Cr-rich bcc phase only. • Spinodal decomposition was observed in AlNi-rich bcc phase only. • Mössbauer spectra of AlxFeCrCoNi were decomposed into subspectra of respective phases. [ABSTRACT FROM AUTHOR]