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Refractory high‐entropy alloys (RHEAs) with excellent high‐temperature performance are attractive for high‐temperature structural applications. However, many RHEAs suffer from high density and poor room temperature (RT) malleability. Herein, the effects of Ti and Nb contents on the phase equilibrium and mechanical properties of HfZrVTaMoWTixNby RHEAs are studied to achieve unique balanced properties in a wide temperature range. With the increase of Ti or Nb content, the Laves phase precipitation is suppressed and RT malleability is improved. Particularly, the HfZrVTaMoWTi2Nb2 RHEA without Laves precipitates exhibits a high yield strength of 1.7 GPa and a compressive strain of ∼30% at RT. Moreover, it retains a high systemic yield strength of 31 MPa cm3 g−1 at 1200 °C, which is nearly three times that of HfZrTaTiNb and nearly equal to that of MoWTaNb, suggesting its potential applicability at elevated temperatures. [ABSTRACT FROM AUTHOR]

Recently, eutectic high-entropy alloys (EHEAs) have become a hotspot in the realm of metal materials because of their superior castability and excellent mechanical properties. Among these, the CoCrFeNi-M (M = Al, Nb, Ta, Zr, and Hf) system has been the most widely investigated. However, most of these are composed of four to five elements, which hinder the emergence of new alloy components with promising properties. A modified simple mixture method was proposed to systematically design EHEAs containing more than five elements in CoCrFeNi-M (Nb, Ta, Zr, and Hf) EHEAs to further expand the compositional space. Following this strategy, four novel senary and septenary EHEAs consisting of face-centered cubic and Laves phase were designed and prepared, indicating the validity and accuracy of this method. The two senary EHEAs showed attractive peak strength of 592 and 660 MPa at 1073 K. They were, therefore, superior to most reported EHEAs, and even better than some reported refractory high-entropy alloys (RHEAs). This study provided a significant paradigm for designing EHEAs with more than five elements. • A simple method to design EHEAs containing more than five elements was proposed. • Four novel EHEAs were designed and prepared based on the simple method. • The CoCrFeNiNb 0.25 Ta 0.20 EHEA showed excellent mechanical properties. [ABSTRACT FROM AUTHOR]

Refractory high-entropy alloys (RHEAs) have attracted extensive attention due to their outstanding high-temperature performance. However, high density and poor ductility are the two bottleneck problems in industrial application. This study aims to exploit novel RHEAs with high specific strength and good ductility by adding light Group IVB elements. The effect of Zr on the as-cast microstructure, density, and mechanical properties of Ti 2 VNbMoZr x (x = 1, 1.5, 2, and 3) RHEAs was investigated in detail. All Ti 2 VNbMoZr x RHEAs exhibited a disordered body-centered-cubic solid-solution phase. The as-cast microstructures changed from dendritic morphology (x = 1 and 1.5) to equiaxed dendritic morphology grain (x = 2 and 3) with the increasing Zr content. The Ti 2 VNbMoZr 2 RHEA displayed optimal mechanical properties with a compressive yield strength of 1421 MPa, a plastic strain of 31.6%, and a specific yield strength of 211 kPa · m3 · kg−1, superior to the most-reported RHEAs. The microbands along {110} and {112} slip planes, which was a typical poly slip configuration, were observed in the Ti 2 VNbMoZr 2 alloy after compression test using ex-situ transmission electron microscopy. Furthermore, the Ti 2 VNbMoZr 2 RHEA exhibited good high-temperature mechanical properties, showing a yield strength of 977 MPa at 600 °C and 386 MPa at 800 °C without fracture at a plastic strain of 50%. The solution strengthening model revealed that the high yield strength of Ti 2 VNbMoZr x RHEAs was mainly derived from the atomic radius misfit and shear modulus misfit of the Zr atoms. • This work proposed a novel Ti 2 VNbMoZr 2 RHEA with a specific yield strength of 211 kPa·m3·kg−1. • The Ti 2 VNbMoZr 2 RHEA exhibited a yield strength of 977 MPa at 600 °C and 386 MPa at 800 °C. • The solution strengthening model revealed that the atomic misfit of the Zr atoms mainly caused the high strength. [ABSTRACT FROM AUTHOR]

Tribological behavior of the model AlCoCrFeNi 2.1 eutectic high-entropy alloy (EHEA) sliding against different counterfaces including Al 2 O 3 , Si 3 N 4 , SiC ceramics and GCr15 steel at room temperature (RT), and particularly SiC at elevated temperatures were investigated. Our EHEA was found to maintain high hardness (＞197 HV) up to 900 °C. The RT tribology tests show that the friction and wear of the EHEA are slightest when against SiC. The wear rates of the EHEA increases monotonously from RT to 900 °C, but the friction coefficient drops sharply (＜0.35) when the temperature exceeds 600 °C. This is attributed to the enhancing in the oxidative wear and the formation of deformed fine-grained layer beneath the worn surface. Image 1 • Tribological behavior of the AlCoCrFeNi 2.1 EHEA against different counterfaces was investigated. • The EHEA/SiC tribo-pair shows the optimal compatibility at RT. • The high hardness of over 197 HV of the EHEA could be maintained up to 900 °C, superior to the Inconel 718 superalloy. • The EHEA exhibits good wear resistance over a wide temperature range from RT to 900 °C. [ABSTRACT FROM AUTHOR]

NbMoTaW-based refractory high-entropy alloys (RHEAs) are now at the research frontier of advanced metallic materials due to outstanding mechanical properties at elevated temperatures. However, the poor plasticity of NbMoTaW-based RHEAs at room temperature hinders further development. The present work proposes a new strategy to tailor in-situ forming heterogeneous structures and improve the room-temperature mechanical properties of NbMoTaW-based RHEAs. A novel series of as-cast Zr x NbMoTaW (x = 0.1, 0.5, and 1, denoted by Zr0.1, Zr0.5, and Zr1, respectively) RHEAs was designed and prepared. The effect of Zr on the mechanical properties and microstructure evolution was investigated. The Zr1 alloy had a compressive yield strength of 1558 MPa and a strain of 15.8% at room temperature, superior to most reported NbMoTaW-based RHEAs. Surprisingly, the Zr1 alloy also showed an ultra-high strength at 1000 °C, which compressive yield strength was 555 MPa without fracture at the strain of 25%. Moreover, all Zr x NbMoTaW RHEAs were composed of two disordered body-centered cubic (BCC) phases. The nanoindentation results showed that the hardness of the dendrite exceeded that of the interdendritic region. Such heterogeneous structure of the Zr1 alloy had a hetero-deformation-induced enhancing effect on strength and plasticity. The heterogeneous structure was mainly triggered by increased mixing enthalpy, severe lattice distortion, and non-equilibrium solidification. The double cross slipping was the dominant deformation mechanism of the Zr1 alloy, which served as a new dislocation source besides the Frank-Read one. Accordingly, the dislocation multiplication was promoted, enhancing the strength and plasticity. This study successfully introduced a high-strength and high-plasticity NbMoTaW-based RHEA, gaining more insight into the alloy design strategies of RHEAs. • This work proposes a strategy by tailoring heterogeneous structure to improve the mechanical properties of RHEAs. • The mechanical properties of ZrNbMoTaW alloy are superior to the most of NbMoTaW-based RHEAs. • Hetero-deformation-induced effect and enhanced dislocations' multiplication were the origins of the outstanding performance. [ABSTRACT FROM AUTHOR]