Abstract
Abstract High-entropy alloys (HEAs) have become a research focus because of their easy access to nanostructures and the characteristics of high strength, hardness, wear resistance, and oxidation resistance, and have been applied in aerospace lightweight materials, ultrahigh temperature materials, high-performance materials, and biomimetic materials. At present, the study of HEAs mainly focuses on the microstructure and mechanical properties. HEAs of Mo, Ti, V, Nb, Hf, Ta, Cr, and W series have high strength, while HEAs of Fe, Co, Ni, Cr, Cu, and Mn series have good toughness. However, the emergence of medium-entropy alloys, metastable HEAs, dual-phase HEAs, and multiphase HEAs increased the complexity of the HEA system, and the phase transition mechanism and strengthening and toughening mechanisms were not fully established. In this article, the preparation, phase formation, phase transformation as well as strengthening and toughening mechanisms of the HEAs are reviewed. The inductive effects of alloying elements, temperature, magnetism, and pressure on the phase transformation were systematically analyzed. The strengthening mechanisms of HEAs are discussed, which provides a reference for the design and performance optimization of HEAs.
Highlights
In the early stage of the development of high-entropy alloys (HEAs), the concept was that five or more elements were alloyed according to equiatomic ratio to form a single-phase solid solution [1–3]
The phase structure of HEAs after alloying is related to the type and content of elements, such as Ti, Al, and V that can promote the formation of body-centered cubic (BCC) structure, while Cu and Co can promote the formation of face-centered cubic (FCC) structure [84]
The CuCoNiCrAlxFe was prepared by Yeh et al [22], with the Al content from 0 to 2.8 at%, and the HEA changed from FCC to BCC structure
Summary
In the early stage of the development of high-entropy alloys (HEAs), the concept was that five or more elements were alloyed according to equiatomic ratio to form a single-phase solid solution [1–3]. Phase transformation and strengthening mechanisms of nanostructured HEAs 1117 type of crystal structure is an important factor to control the strength, hardness, and plasticity of HEAs. The crystal structure of the HEAs is closely related to the thermodynamic parameters [9,10]. By reducing the phase stability and promoting phase transformation induced plastic (TRIP) deformation effect, the synergistic strength and toughness of HEAs can be achieved [18–21], mainly including the transformation between BCC and FCC [22,23] and from FCC to close-packed hexagonal (HCP) [24,25]. In order to optimize the mechanical properties of HEAs, many effective methods have been proposed, such as composition control [22,23], adding reinforcements [26,27], twin induced plastic (TWIP) deformation effect [28,29] and TRIP effect [20,21]. The mechanisms of strengthening and toughening were summarized, and the similarities and differences between the HEAs and the traditional alloy in the mechanism were analyzed, hoping to provide a theoretical basis for the optimization design of mechanical properties of the HEAs
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