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Additive manufacturing (AM) is a promising approach to producing high- or medium-entropy alloys (HEAs or MEAs) with excellent properties. However, some undesirable microstructural defects and unstable precipitated phases were formed owing to the repeated heating and cooling steps and the rapid solidification nature of the AM process. Annealing treatment after AM fabrication is often beneficial for adjusting the comprehensive mechanical properties and stabilizing the microstructures. In this study, a VCoNi MEA single wall sample was fabricated successfully via laser melting deposition (LMD), and the effects of post-annealing treatments on the microstructures and mechanical properties were explored. The grain size and σ-phase particle size increase and the σ-phase particles undergo fragmentation, spheroidization, and coarsening during annealing. As the annealing time increases, the tensile strain increases, but the tensile strength decreases. An excellent combination of strength and ductility can be obtained after annealing for 1.5 h (The yield strength, ultimate tensile strength, and tensile strain are 741.2 MPa, 1287.8 MPa, and 30.5 %, respectively). HDI hardening is the most important strengthening mechanism in this work. The decrease in tensile stress after the annealing treatment is mainly attributed to the decrease of heterogeneity of microstructure, and the increase in tensile strain after the annealing treatment is mainly attributed to the decrease of the pores and the spheroidization of the rod-like σ-phase particles. This work provides practical insight into adjusting the microstructure and comprehensive mechanical properties of HEAs and MEAs for AM. • Excellent combination of strength (1287.8 MPa) and ductility (30.5 %) can be obtained after the annealing of 1.5h. • The increase of elongation after annealing is attributed to the degradation of the pores and the rod-like σ phase particles. • Microstructures and mechanical properties of the LMD VCoNi sample can be adjusted by suitable annealing. [ABSTRACT FROM AUTHOR]

Eutectic high-entropy alloys (EHEAs), combined with good castability and exceptional properties, are becoming hotpots in the field of metallic materials. It is worth noting that the most reported EHEAs are composed of metallic elements, and the EHEAs containing non-metallic elements have been rarely reported. In this work, four novel EHEAs containing B and Si with face-centered-cubic and M 3 B 2 -type boride were designed and prepared. After a simple annealing, they exhibited high ultimate tensile strength (1048 MPã1140 MPa) and good fracture ductility (4.1%–14.7%). Compared with the as-cast alloys, the fracture ductility of the four annealing EHEAs increases by 3.4–6.1 times, while the ultimate tensile strength shows practically no reduction. The outstanding mechanical properties were attributed to the fragmentation and spheroidization of M 3 B 2 -type boride, which not only reduces the nucleation positions of microcracks, but also widens the distance across which the cracks connect. • By introducing nonmetallic elements, four new EHEAs containing B/Si elements were designed and prepared. • The four EHEAs show good heat modification. By annealing, the serrated boride is fully spheroidized into spherical-shaped. • The four annealing EHEAs showed high UTS (1048∼1140MPa) and good ductility (4.1∼14.7%). • Compared with as-cast, the ductility of the four annealing EHEAs increases by 3.4∼6.1 times, and the UTS almost not lose. [ABSTRACT FROM AUTHOR]

• Strength and ductility can be improved simultaneously via simple annealing. • An annealed hypo-EHEA with ultimate tensile strength ∼1410 MPa and elongation ∼15.7 %. • Spherical eutectic phase provides more space for dislocation slip and improves strain-hardening ability. Eutectic high-entropy alloys (EHEAs), combining the advantages of traditional eutectic alloys and high-entropy alloys (HEAs), have become a promising multi-principal alloy system for industrial application. Further improving the strength-ductility of EHEAs has been the pursuit of researchers. In this work, we found that the strength and ductility can be improved simultaneously in a new class EHEAs with serrated eutectic structure via simple spheroidizing annealing. As a manifestation of this fascinating discovery, an Al 0.25 CoCrFeNi 2 V 0.8 B 0.4 EHEA was developed that was composed of face-centered cubic (FCC) and serrated boride phase and then subjected to spheroidizing annealing. The ultimate tensile strength (UTS) and elongation (EL) increased from 1193 MPa, 4.3 % (in as-cast) to 1410 MPa, 15.7 % after spheroidizing annealing. This combined increase in strength and ductility was attributed to that the serrated boride eutectic phase is spheroidized into a dispersed spherical eutectic phase, which effectively alleviates the stress concentration and provides more space for dislocation slip, promoting strain-hardening ability during deformation. This work provides valuable insight into the development of high-performance EHEAs. [ABSTRACT FROM AUTHOR]

In the present work, we studied the effects of transition metal elements on microstructure evolution and high-temperature mechanical properties via the preparation of new modified alloys with micro-additions of Cr, Ti, V, Zr, Mo, and Mn to address the poor high-temperature performance of Al–Si–Cu–Mg alloys for automotive engines. The results show that the addition of transition metal elements formed a variety of new intermetallic phases that were stable at high temperatures, such as (AlSi)3(TiVZr), (AlSi)3Ti, (AlSi)3(CrVTi), Al74Si6Mn4Cr2Fe, Al85Si5Mn2Mo2CrFe, Al0.78Fe4.8Mn0.27Mo4.15Si2, (AlSi)2(CrVTi)Mo, and Al13(MoCrVTi)4Si4, and these phases evidently improved the ultimate high-temperature tensile strength and yield strength. The ultimate tensile strength and yield strength of the modified alloy increased by 17.49% and 31.65% when the test temperature increased to 240 °C, respectively, and by 71.28% and 74.73% when the test temperature increased to 300 °C, respectively. The fundamental reason for this change is that the intermetallic phase hinders the expansion of cracks, which can exist stably at high temperatures. When a crack extends to the intermetallic phases, it will break along with the intermetallic phases or propagate along the morphological edge of the intermetallic phases. [ABSTRACT FROM AUTHOR]