Additive manufactured high entropy alloys:A review of the microstructure and properties

High entropy alloys (HEAs) are promising multi-component alloys with unique combination of novel microstructures and excellent properties. However, there are still certain limitations in the fabrication of HEAs by conventional methods. Additive manufactured HEAs exhibit optimized microstructures and improved properties, and there is a significantly increasing trend on the application of additive manufacturing (AM) techniques in producing HEAs in recent years. This review summarizes the additive manufactured HEAs in terms of microstructure characteristics, mechanical and some functional properties reported so far, and provides readers with a fundamental understanding of this research field. We first briefly review the application of AM methods and the applied HEAs systems, then the microstructure including the relative density, residual stress, grain structure, texture and dislocation networks, element distribution, precipitations and the influence of post-treatment on the microstructural evolution, next the mechanical properties consisting of hardness, tensile properties, compressive properties, cryogenic and high-temperature properties, fatigue properties, creep behavior, post-treatment effect and the strengthening mechanisms analysis. Thereafter, emerging functional properties of additive manufactured HEAs, namely the corrosion resistance, oxidation behaviors, magnetic properties as well as hydrogen storage properties are discussed, respectively. Finally, the current challenges and future work are proposed based on the current research status of this topic

Effect of Nitrogen Pressure on the Fabrication of AlCrFeCoNiCu0.5 High Entropy Nitride Thin Films via Cathodic Arc Deposition

High entropy alloys (HEAs), consisting of five or more than five elements in equal or nearly equal proportions, usually exhibit superior mechanical properties, outstanding corrosion & oxidation resistance, and exceptionally high thermal stability compared to traditional alloys. HEA thin films possess further improved mechanical properties due to their nanocrystalline microstructure. Compared to HEA thin films, high entropy nitrides (HENs) have even higher mechanical strength and chemical inertness. AlCrFeCoNiCu0.5 HEN thin film is reported to be an extraordinarily hard material that possesses high levels of surface protective nitrides layer, while limited work of AlCrFeCoNiCu0.5 HEN thin film deposited by cathodic arc has been done. In this work, AlCrFeCoNiCu0.5 HEN thin films were deposited on (100) Si wafer using a filtered cathodic arc. The nitrogen concentration for each thin film was regulated by changing pressure during depositions, tuning the distortion energy and mechanical properties. STEM-EDS revealed increased aluminium concentration as pressure increased. X-ray photoelectron spectra revealed that AlN was the preferred nitride formed. Interstitial solid solution of nitrogen enhanced the lattice distortion in the HEN films, while stronger covalent bonds contracted the crystal lattice according to XRD and HRTEM images. Amorphization was observed in the thin film with increased pressure. The mechanical properties of the cathodic arc deposited AlCrFeCoNiCu0.5 HEN thin films were found to improve when pressure increased with the highest hardness of 12.4 0.6 GPa and elastic modulus of 347.3 17.7 GPa found at the highest pressure of 0.05 Pa. These mechanical properties were significantly enhanced compared to those of similar films fabricated by RF magnetron sputtering