We designed a novel Co-free AlCrFe2Ni2Ti0.5 high-entropy alloy (HEA) that features an excellent combination of strength and ductility in this study. The as-cast AlCrFe2Ni2Ti0.5 alloy showed equiaxed grains undergoing spinodal decomposition, which consisted of ultrafine-grained laminated body-centered cubic (bcc) phases and an ordered body-centered cubic (b2) phase, and some precipitates embedded in the b2 matrix. The bcc and b2 phases also feature a coherent interface. This unique structure impedes mobile dislocations and hinders the formation of cracks, thereby giving the AlCrFe2Ni2Ti0.5 HEA both high strength and plasticity. At room temperature, the as-cast AlCrFe2Ni2Ti0.5 alloy exhibited a compressive yield strength of 1714 MPa, an ultimate strength of 3307 MPa, and an elongation of 43%. These mechanical properties are superior to those of most reported HEAs.
This study aimed to investigate the microstructure and mechanical properties of TixZrVNb (x = 1, 1.5, 2) refractory high-entropy alloys at room and elevated temperatures. The TiZrVNb alloy consisted of the body-centered cubic (bcc) matrix with a small amount of V2Zr phase. The Ti1.5ZrVNb and Ti2ZrVNb alloys exhibited a single-phase bcc structure. At room temperature, the tensile ductility of the as-cast alloys increased from 3.5% to 12.3% with the increase in the Ti content. The TixZrVNb alloys exhibited high yield strength at 600°C, and the ultimate yield strength was more than 900 MPa. Softening occurred at 800°C, but the ultimate yield strength could still exceed 200 MPa. Moreover, the TixZrVNb alloys displayed low densities but high specific yield strengths (SYSs). The lowest density of TixZrVNb alloys was only 6.12 g/cm3, but the SYS could reach about 180 MPa·cm3·g−1, which is better than those of most reported high-entropy alloys (HEAs).
We prepared (CuCoFeNi)Tix (x = 0, 0.2, 0.4, 0.6, 0.8, and 1.0) high-entropy alloys (HEAs) by vacuum arc melting and then investigated the effects of Ti on their microstructure and mechanical properties. When x was inreased to 0.6, the structure of the alloy transformed from their initial single face-centered cubic (fcc) structure into fcc+Laves mixed structure. The Laves phase was found to comprise Fe2Ti and be mainly distributed in the dendrite region. With increasing Ti content, both the Laves phase and the hardness of the alloy increased, whereas its yield and fracture strengths first increased and then decreased, reaching their highest value when x was 0.8. The (CuCoFeNi)Ti0.8 alloy exhibited the best overall mechanical properties, with yield and fracture strengths of 949.7 and 1723.4 MPa, respectively, a fracture strain of 27.92%, and a hardness of HV 461.6.
AlCrFeNiCuNbx (x = 0.05, 0.15, and 0.26) high-entropy alloys (HEAs) were successfully fabricated using the laser metal deposition technique. The laser power of 1600 W and scanning speed of 1.2 m/min were used during laser processing of the alloys. The microstructural, mechanical, and electrochemical characteristics of the alloys were evaluated using various advanced characterization techniques. Results showed that the alloys exhibited a dual-phase structure with dendritic grains. The inclusion of Nb in the AlCrFeNiCu alloy matrix promoted the formation of fine eutectic structures and changed the shape of the grains from columnar to equiaxed. The Cu content decreased with the increase in the content of Nb, whereas the Al content increased with the increase in the content of Nb. The findings indicated that the presence of Nb in the alloy promoted the formation and enhanced the stability of the body-centered cubic (bcc) phase. All of the alloys that contained Nb also exhibited high hardness, compressive strength, and wear resistance. Furthermore, the low current density and positive shift in potential exhibited by HEAs with appropriate addition of Nb highlighted the superior anticorrosive properties.
The evolution of the microstructure and tensile properties of dual-phase Al0.6CoCrFeNi high-entropy alloys (HEAs) subjected to cold rolling was investigated. The homogenized Al0.6CoCrFeNi alloys consisted of face-centered-cubic and body-centered-cubic phases, presenting similar mechanical behavior as the as-cast state. The yield and tensile strengths of the alloys could be dramatically enhanced to ~1205 MPa and ~1318 MPa after 50% rolling reduction, respectively. A power-law relationship was discovered between the strain-hardening exponent and rolling reduction. The tensile strengths of this dual-phase HEA with different cold rolling treatments were predicted, mainly based on the Hollomon relationship, by the strain-hardening exponent, and showed good agreement with the experimental results.
A new method of high-gravity combustion synthesis (HGCS) followed by post-treatment (PT) is reported for preparing high-performance high-entropy alloys (HEAs), Cr0.9FeNi2.5V0.2Al0.5 alloy, whereby cheap thermite powder is used as the raw material. In this process, the HEA melt and the ceramic melt are rapidly formed by a strong exothermic combustion synthesis reaction and completely separated under a high-gravity field. Then, the master alloy is obtained after cooling. Subsequently, the master alloy is sequentially subjected to conventional vacuum arc melting (VAM), homogenization treatment, cold rolling, and annealing treatment to realize a tensile strength, yield strength, and elongation of 1250 MPa, 1075 MPa, and 2.9%, respectively. The present method is increasingly attractive due to its low cost of raw materials and the intermediate product obtained without high-temperature heating. Based on the calculation of phase separation kinetics in the high-temperature melt, it is expected that the final alloys with high performance can be prepared directly across master alloys with higher high-gravity coefficients.
Friction stir processing of an Al0.1CoCrFeNi high entropy alloy (HEA) was performed at controlled cooling conditions (ambient and liquid submerged). Microstructural and mechanical characterization of the processed and as-cast HEAs was evaluated using electron backscatter diffraction, micro-hardness testing and nanoindentation. HEA under the submerged cooling condition showed elongated grains (10 μm) with fine equiaxed grains (2 μm) along the boundary compared to the coarser grain (~2 mm) of as-cast HEA. The hardness showed remarkable improvements with four (submerged cooling condition) and three (ambient cooling condition) times that of as-cast HEA (HV ~150). The enhanced hardness is attributed to the significant grain refinement in the processed HEAs. Cavitation erosion behavior was observed for samples using an ultrasonication method. All of the HEAs showed better cavitation erosion resistance than the stainless steel 316L. The sample processed under a submerged liquid condition showed approximately 20 and 2 times greater erosion resistance than stainless steel 316L and as-cast HEA, respectively. The enhanced erosion resistances of the processed HEAs correlate to their increased hardness, resistance to plasticity, and better yield strength than the as-cast HEA. The surface of the tested samples showed nucleation and pit growth, and plastic deformation of the material followed by fatigue-controlled disintegration as the primary material removal mechanism.
Using thermochemical treatments, boronized layers were successfully prepared on Al0.25CoCrFeNi high-entropy alloys (HEAs). The thickness of the boronized layers ranged widely from 20 to 50 μm, depending on the heat treatment time. Boronizing remarkably improved the surface hardness from HV 188 to HV 1265 after treating at 900°C for 9 h. Moreover, boronizing enhanced the yield strength of HEAs from 195 to 265 MPa but deteriorated the tensile ductility. Multiple crackings in the boride layers significantly decreased the plasticity. The insufficient work-hardening capacity essentially facilitated the plastic instability of the boronized HEAs. With decreasing substrate thickness, the fracture modes gradually transformed from dimples to quasi-cleavage and eventually to cleavage.
This paper demonstrates an intrinsic modulation of the cutoff wavelength in the spectra for solar selective absorbing coating based on high-entropy films. The (NiCuCrFeSi)N ((NCCFS)N) films were deposited by a magnetron sputtering system. Rutherford backscattering spectroscopy analysis confirms the uniform composition and good homogeneity of these high-entropy films. The real and imaginary parts of the permittivity for the (NCCFS)N material are calculated on the basis of the reflectance spectral fitting results. A redshift cutoff wavelength of the reflectance spectrum with increasing nitrogen gas flow rate exists because of the different levels of dispersion when changing nitrogen content. To realize significant solar absorption, the film surface was reconstituted to match its impedance with air by designing a pyramid nanostructure metasurface. Compared with the absorptance of the as-deposited films, the designed metasurface obtains a significant improvement in solar absorption with the absorptance increasing from 0.74 to 0.99. The metasurfaces also show low mid-infrared emissions with thermal emittance that can be as low as 0.06. These results demonstrate a new idea in the design of solar selective absorbing surface with controllable absorptance and low infrared emission for high-efficiency photo-thermal conversion.
High-entropy alloys (HEAs) generally possess complex component combinations and abnormal properties. The traditional methods of investigating these alloys are becoming increasingly inefficient because of the unpredictable phase transformation and the combination of many constituents. The development of compositionally complex materials such as HEAs requires high-throughput experimental methods, which involves preparing many samples in a short time. Here we apply the high-throughput method to investigate the phase evolution and mechanical properties of novel HEA film with the compositional gradient of (Cr,Fe,V)–(Ta,W). First, we deposited the compositional gradient film by co-sputtering. Second, the mechanical properties and thermal stability of the (Cr0.33Fe0.33V0.33)x(Ta0.5W0.5)100−x (x = 13–82) multiple-based-elemental (MBE) alloys were investigated. After the deposited wafer was annealed at 600°C for 0.5 h, the initial amorphous phase was transformed into a body-centered cubic (bcc) structure phase when x = 33. Oxides were observed on the film surface when x was 72 and 82. Finally, the highest hardness of as-deposited films was found when x = 18, and the maximum hardness of annealed films was found when x = 33.
The effects of substrate temperature and deposition time on the morphology and corrosion resistance of FeCoCrNiMo0.3 coating fabricated by magnetron sputtering were investigated by scanning electron microscopy and electrochemical tests. The FeCoCrNiMo0.3 coating was mainly composed of the face-centered cubic phase. High substrate temperature promoted the densification of the coating, and the pitting resistance and protective ability of the coating in 3.5wt% NaCl solution was thus improved. When the deposition time was prolonged at 500°C, the thickness of the coating remarkably increased. Meanwhile, the pitting resistance improved as the deposition time increased from 1 to 3 h; however, further improvement could not be obtained for the coating sputtered for 5 h. Overall, the pitting resistance of the FeCoCrNiMo0.3 coating sputtered at 500°C for 3 h exceeds those of most of the reported high-entropy alloy coatings.
Refractory high-entropy alloys (RHEAs) are emerging as new materials for high temperature structural applications because of their stable mechanical and thermal properties at temperatures higher than 2273 K. In this study, the mechanical properties of MoNbTaTiW RHEA are examined by applying calculations based on first-principles density functional theory (DFT) and using a large unit cell with 100 randomized atoms. The phase calculation of MoNbTaTiW with CALPHAD method shows the existence of a stable body-centered cubic structure at a high temperature and a hexagonal closely packed phase at a low temperature. The predicted phase, shear modulus, Young’s modulus, Poisson’s ratio, and hardness values are consistent with available experimental results. The linear thermal expansion coefficient, vibrational entropy, and vibrational heat capacity of MoNbTaTiW RHEA are investigated in accordance with Debye–Grüneisen theory. These results may provide a basis for future research related to the application of RHEAs.
To clarify the effect of pressure on a (TaNb)0.67(HfZrTi)0.33 alloy composed of a solid solution with a single body-centered-cubic crystal structure, we used first-principles calculations to theoretically investigate the structural, elastic, and electronic properties of this alloy at different pressures. The results show that the calculated equilibrium lattice parameters are consistent with the experimental results, and that the normalized structural parameters of lattice constants and volume decrease whereas the total enthalpy difference ΔE and elastic constants increase with increasing pressure. The (TaNb)0.67(HfZrTi)0.33 alloy exhibits mechanical stability at high pressures lower than 400 GPa. At high pressure, the bulk modulus B shows larger values than the shear modulus G, and the alloy exhibits an obvious anisotropic feature at pressures ranging from 30 to 70 GPa. Our analysis of the electronic structures reveals that the atomic orbitals are occupied by the electrons change due to the compression of the crystal lattices under the effect of high pressure, which results in a decrease in the total density of states and a wider electron energy level. This factor is favorable for zero resistance.
The quasi-metallic fibers were selected from 1 to 40 pieces and connected in parallel in this study. The giant magneto impedance (GMI) effect of Co-based melt extract fibers in the bundle mode was investigated, and the distribution of the surface circumferential magnetic field on the fibers was also analyzed. Such distribution was induced by the driving current, which gave rise to the circular magnetization process and the GMI effect. The improved GMI effect with much higher field sensitivity was observed in these fiber bundles. Results show that the field sensitivities of the four-fiber and six-fiber bundles reach 19.5 V·m·kA−1 (at 1 MHz) and 30.8 V·m·kA−1 (at 5 MHz). The circumferential magnetic field distributed throughout the fiber’s circumferential surface is rearranged and becomes uneven due to the magnetic interaction among fibers. There are both strengthened and weakened magnetic field parts around these fibers’ surfaces. The strengthened magnetic field improves the circumferential domain magnetization of the surface, resulting in larger GMI effects. However, the weakened parts inhibit the circumferential magnetization process and, therefore, the GMI effect. This also induces greater magnetization damp because of the increased domain interactions under the strong skin effect. The co-effect between the magnetic domains and the circumferential magnetization induces the optimization of the GMI effect in the four-fiber bundles. The observed GMI effect proves that fibers in bundle form can modify the sensitivity of the GMI effect. Moreover, different fiber bundles could be tuned according to the working conditions in order to manipulate the GMI response.