High entropy alloys: A focused review of mechanical properties and deformation mechanisms

Mechanical behavior of high-entropy alloys

Boosted by the success of high-entropy alloys (HEAs) manufactured by conventional processes in various applications, the development of HEAs for 3D printing has been advancing rapidly in recent years. 3D printing of HEAs gives rise to a great potential for manufacturing geometrically complex HEA products with desirable performances, thereby inspiring their increased appearance in industrial applications. Herein, a comprehensive review of the recent achievements of 3D printing of HEAs is provided, in the aspects of their powder development, printing processes, microstructures, properties, and potential applications. It begins with the introduction of the fundamentals of 3D printing and HEAs, as well as the unique properties of 3D-printed HEA products. The processes for the development of HEA powders, including atomization and mechanical alloying, and the powder properties, are then presented. Thereafter, typical processes for printing HEA products from powders, namely, directed energy deposition, selective laser melting, and electron beam melting, are discussed with regard to the phases, crystal features, mechanical properties, functionalities, and potential applications of these products (particularly in the aerospace, energy, molding, and tooling industries). Finally, perspectives are outlined to provide guidance for future research.

Recent Advances on High‐Entropy Alloys for 3D Printing

High-entropy alloys (HEAs) are a class of metallic materials that have revolutionized alloy design. They are known for their high compressive strengths, often greater than 1 GPa; however, the tensile strengths of most reported HEAs are limited. Here, we report a strategy for the design and fabrication of HEAs that can achieve ultrahigh tensile strengths. The proposed strategy involves the introduction of a high density of hierarchical intragranular nanoprecipitates. To establish the validity of this strategy, we designed and fabricated a bulk Fe25Co25Ni25Al10Ti15 HEA to consist of a principal face-centered cubic (fcc) phase containing hierarchical intragranular nanoprecipitates. Our results show that precipitation strengthening, as one of the main strengthening mechanisms, contributes to a tensile yield strength (σ0.2) of ~1.86 GPa and an ultimate tensile strength of ~2.52 GPa at room temperature, which heretofore represents the highest strength reported for an HEA with an appreciable failure strain of ~5.2%.

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A high-entropy alloy with hierarchical nanoprecipitates and ultrahigh strength

Mechanical alloying (MA) followed by sintering has been one of the most widely adopted routes to produce nanocrystalline high-entropy alloys (HEAs). Enhanced solid solubility, room temperature processing, and homogenous alloy formation are the key benefits provided by MA. Spark plasma sintering has largely been used to obtain high-density HEA pellets from milled powders. However, there are many challenges associated with the production of HEAs using MA, which include contamination during milling and high propensity of oxidation. The present review provides a comprehensive understanding of various HEAs produced by MA so far, with the aim to bring out the governing aspects of phase evolution, thermal stability, and properties achieved. The limitations and challenges of the process are also critically assessed with a possible way forward. The paper also compares the results obtained from high-pressure torsion, another severe plastic deformation technique.

https://www.cambridge.org/core/services/aop-cambridge-core/content/view/8B9B1E7CDF719FA7C418330BFEF45912/S0884291419000372a.pdf/div-class-title-high-entropy-alloys-by-mechanical-alloying-a-review-div.pdf

Jozef Zapletal

Papers

Microstructure and mechanical properties of Ni1,5Co1,5CrFeTi0,5 high entropy alloy fabricated by mechanical alloying and spark plasma sintering