Enhancing the mechanical properties of high-entropy alloys through severe plastic deformation: A review

High-entropy alloys (HEAs) are one of the breakthroughs in the past decade in alloy development that have the potential to exhibit outstanding physical, mechanical, and chemical properties. This allows HEAs to be highly versatile materials for use in a variety of applications. Through reasonable composition design and post-manufacturing processes, HEAs can show superior properties compared to traditional alloys, which are highly demanded for novel emerging technologies. Severe plastic deformation (SPD) has been known as one of the most popular post-manufacturing processes for enhancing the mechanical properties of HEAs. However, there is still a lack of knowledge about the microstructure, physical, and mechanical properties of HEAs subjected to SPD processes. This review is concerned with the production of nano/ultrafine-grained HEAs using SPD techniques such as severe cold rolling (SCR), high-pressure torsion (HPT), and equal channel angular pressing (ECAP). Also, the characteristics of HEAs with respect to SPD are demonstrated, such as reduced grain growth and phase decomposition. These characteristics increase the possibility of producing nanostructured high-entropy alloys (NsHEAs) with multiple principal elements by SPD processes or by post-annealing and enable extremely high superplasticity at high strain rates. Finally, these findings introduce SPD as not only a processing tool to improve the physical and mechanical properties of HEAs, but also as a synthesis tool to fabricate novel HEAs with superior properties compared to conventional engineering materials, especially for high-tech applications

Use of laser cladding for the synthesis of coatings from high-entropy alloys reinforced with ceramic particles

The purpose of this work was to develop methods for obtaining composite coatings based on high-entropy alloys by laser cladding from mixtures of low-entropy powders. Powders of pure copper (Cu), titanium carbide (TiC), aluminum oxide (Al2O3), as well as commercial powders of low- and medium-entropy alloys were used for the implementation of laser additive technologies. The powder particle size ranged from 40 to 150 µm. Coatings were obtained using an ytterbium fiber-optic laser on a steel substrate. The structure of experimental samples was studied on a scanning electron microscope. In order to confirm the composition of the zones found in the studied samples (for chemical and structural analysis of phases in the studied samples), X-ray spectral microanalysis was performed using an energy-dispersive X-ray spectrometer. The phase structure of the obtained samples was studied by X-ray phase analysis using a powder diffractometer using Cu-Kα radiation. The technique used made it possible to obtain composite coatings with inclusions of Al2O3 and TiC. The results of the work open the way to the development of technologies for producing, by laser cladding, highly functional coatings from high-entropy alloys strengthened with reinforcing ceramic particles or from composite materials based on high-entropy alloys, using a combination of commercially available powders of low-entropy and medium-entropy alloys