Eutectic is typically utilized in their as-cast state in industrial applications on account of excellent castability. However, unlike conventional alloys with superior plasticity need to improve strength, the eutectic high-entropy alloys (EHEAs) possess considerable strength but suffer from low ductile, starving for high ductility while maintaining strength. Here, we proposed a simple and feasible strategy by reducing the Al/Ni ratio in AlxCo20Fe20Ni60-x EHEAs with lamellar eutectic microstructure to simultaneously increase the volume fraction of soft phase and promote martensitic transformation in hard phase, thereby enhancing plasticity without sacrificing strength. It is found that the Al17.5Co20Fe20Ni42.5 alloy exhibits a hypoeutectic FCC/BCC microstructure, in which the coarse primary FCC phase facilitates dislocation slip, and the BCC/B2 -> L1(0) martensitic transformation in the post-fracture microstructure enhances strain hardening. As a result, the elongation is increased from similar to 14 % to similar to 27 %, while retaining a tensile ultimate strength of around1040 MPa, comparable to that of the eutectic Al18.5Co20Fe20Ni42.5 alloy (similar to 1071 MPa). This study provides a viable approach for boosting strength and toughness of dual-phase EHEAs solely through composition modulation.

Eutectic high-entropy alloys (EHEAs) exhibit excellent castability and attractive mechanical properties; however, their compositional design flexibility is often limited by the narrow eutectic point, leading to strong compositionproperty sensitivity. In this study, a series of AlCoCrxFeNi2.1 (x = 0.25-1.5) alloys were designed based on phase formation principles and a multi-composition strategy by treating Cr as a balancing element. A continuous eutectic composition range was identified, within which stable lamellar FCC/B2 microstructures were obtained. Remarkably, despite compositional variation, these alloys exhibit nearly constant mechanical performance. The average yield strength and ultimate tensile strength are 602 MPa and 1089 MPa, respectively. Elongation first increases and then decreases with Cr content, reaching a maximum of 16.7% at Cr1.0 alloy. CALPHAD calculations and DSC analysis reveal that an ultranarrow liquidus-solidus temperature interval is maintained across this compositional range, enabling a stable near-eutectic solidification pathway. This strategy effectively mitigates property degradation caused by compositional deviation during processing, offering a practical approach for large-scale manufacturing and additive manufacturing of EHEAs.

In this work, a novel hybrid 2024Al composite reinforced with (TiZrHfTa)C high-entropy ceramic (HEC) particles and AlCoCrFeNi high-entropy alloy (HEA) particles was successfully fabricated by spark plasma sintering. The results show that the single HEC/2024Al composite exhibits a strength-ductility trade-off: increasing the HEC content from 5 vol% to 25 vol% raises the yield strength from 279.5 MPa to 461.8 MPa, but drastically reduces the plastic strain from 25.8% to 3.42%. In contrast, the hybrid composite containing 20 vol% HEC and 5 vol% HEA simultaneously improves both properties, achieving a yield strength of 489.0 MPa (a 5.9% increase) and a plastic strain of 10.12% (a 197% increase) compared to the 25 vol% HEC/2024Al composite. Microstructural characterization reveals the uniform distribution of reinforcements and the formation of a core-shell interfacial structure between the HEA particles and the aluminum matrix, which promotes strong interfacial bonding. Mechanical testing demonstrates that the synergistic effect of the dual HEC-HEA reinforcements significantly enhances the strength of composite while maintaining a useful level of ductility. This work provides a new strategy for designing high-performance AMCs with balanced mechanical properties through the hybrid use of high-entropy ceramic and alloy reinforcements.

A novel x'-strengthened FCC-based Al0.5CoFeNiC0.1 high entropy superalloy (HESA) with minor B2 phase was prepared by arc melting. The FCC/x' dual-phase microstructure with thermal stability is similar to & gamma;/& gamma;' micro-structure of Ni-based superalloys. Surprisedly, the large volume fraction (nearly 50%), high density and nano-scale coherent x' particles with uniform distribution are easily accessible only by direct solidification, which gives rise to superior compressive yield strengths at both room and elevated temperatures, reaching 1130 MPa at 25 degrees C and 830 MPa at 700 degrees C, respectively. The sustained high-temperature yield strength is contributed to both the antiphase boundaries (APBs) and stacking faults (SFs) shearing x' particles. Further, optics and electron microscopy analyses revealed the changes (transition point about at 0.6 Tm, where Tm is melting temperature) of the dominant deformation and failure mechanisms, dependent on the temperature. The dominant deformation mode is planar slip and SFs at relatively low temperatures, while the cross slip and dislocation dissociation above 800 degrees C (0.6 Tm), coupled with the diffusion-controlled recovery mechanisms. The failure mechanism shows failure mode from shearing fracture to thermal softening. Our x'-strengthened FCC-based superalloy provides a route for elevated-temperature applications.

The effect of Mn on the microstructure and tensile properties of Al0.5CoFeNiC0.1 HEA (high-entropy alloy) has been investigated using electron microscopy, atom probe and mechanical testing. The results show that addition of Mn refines dendrite and grain and reduces volume fraction of B2 phase and interdendritic regions. Mn is demonstrated to be not the former of kappa ' phase. Therefore, the addition of Mn reduces the size and volume fraction of the kappa ' phase, leading to a reduction in the yield strength of the HEA whereas an enhancement in ductility. 7.7 at.% Mn doping makes the HEA (Mn0.3) have a good balance between yield strength (1 GPa) and ductility (23% elongation). Adding Mn does not change deformation mechanism of the HEAs.

In the present work, the effect of twin boundary-dislocation and twin boundary-solute atom interaction on detwinning of Mg-2Gd-2Y-0.3Zr alloy has been investigated by annealing treatment and change of loading path. The results show that when the samples were precompressed along transverse direction (TD), unloading, and then recompressed along normal direction (ND), the detwinning is the predominant deformation. However, when the samples precompressed along ND were recompressed along TD, the detwinning of {10 (1) over bar1}-{10 (1) over bar2} double twin is observed difficultly. The {10 (1) over bar2} detwinning can also be suppressed completely if the samples precompressed along TD were annealed and then recompressed along ND. This should be resulted from the segregation of Gd and Y solute atoms at twin boundary during annealing. Thus, the yield strength of the presompressed and annealing samples is increased by about 100 MPa compared with the presompressed samples without annealing during recompressing along ND. (C) 2018 Elsevier B.V. All rights reserved.

In order to explore the influence of hot rolling and annealing treatment on the microstructure and compressive strength of Mg-10Gd-3Y-0.3Zr alloy,an optical metalloscope was used to observe the microstructure of the material rolled at a high temperature and analyze the grain size and the degree of dynamic recrystallization.The result shows that with the deformation increasing,the grain size of Mg-10Gd-3Y-0.3Zr alloy decreases significantly;when the rolling reduction reaches 60%,the grain size is uniform,about 60 μm,and the density of twin crystal is high;when the rolling reduction is less than 60%,the grain size is coarse and the density of twin crystal is low;when the rolling reduction exceeds 60%,the recrystallized grains gradually replace deformed grains,the grain size decreases and twin crystal almost disappears.Annealing treatment can significantly increase the compressive strength of the rolled plate.After annealing treatment at 175 ℃ for 3 hours,the strengthening effect becomes obvious and the compressive strength is 424 MPa.When the annealing temperature exceeds 175 ℃,the strengthening effect begins to decrease.

The influence of the rare earth element yttrium on the dynamic strain aging (DSA)of Mg-3Nd-0.3Zr alloy is investigated.A series of compressive tests were conducted at room temperature and 200 ℃ at a constant rate 4.17×10-5s-1.The results show that the addition of Y causes changes in the type of serration and mechanical properties.The DSA phenomenon occurs at 200 ℃ in Mg-3Nd-0.3Zr and Mg-5Y-3Nd-0.3Zr,whose serrated types are type B and type C.Their critical strains are 4.98% and 2.20%,r,and their probability statistics distributions of stress drop magnitudes are unimodal type and bimodal type,respectively.DSA does no obvious contribution to the enhancement of the strength in Mg-5Y-3Nd-0.3Zr at 200 ℃.Transition of serrated types is related to the difficult diffusion of solute atoms and the impediment of mobile dislocations which are caused by the addition of Y.

The influence of the Gd content on microstructure evolution and mechanical behavior of the Mg-x Gd-0.3Zr magnesium alloy is investigated by optical microscope (OM),X-ray diffraction (XRD),scanning electron microscope (SEM),transmission electron microscope (TEM) and compression test after solution treatment.The results show that the as-cast alloy is mainly composed of α-Mg,eutectic tissue and second phase.After the solution treatment the eutectic phase is completely dissolved,but there is still no undissolved second phase in the grain boundary.With the increase of Gd content,the second phase gradually increases,grain refines,the compression strength and yield strength of the alloys increase linearly.