FeCoNiCrMn High Entropy Alloy Research Articles

Evolution of microstructure and mechanical properties of aluminum matrix composites reinforced with dual-phase heterostructures

The trade-off between strength and plasticity has long been challenging in particle-reinforced aluminum matrix composites (PRAMCs). This study proposes an innovative approach for preparing aluminum matrix composites (AMCs) using a dual-phase hybrid of FeCoNiCrMn high entropy alloy (HEA) and multiscale aluminum oxide (Al2O3) particles. The microstructure evolution and strengthening mechanisms were evaluated through scanning electron microscopy (SEM), electron backscatter diffraction (EBSD), and transmission electron microscopy (TEM). The results demonstrated that the dual-phase particle strengthening resulted from the alternating distribution and synergistic action of HEA and Al2O3 particles within the matrix, forming a continuous strain buffer with a strength gradient. Notably, introducing HEA and nano-Al2O3 led to a higher density of dislocations. Additionally, EBSD analysis revealed a uniform strain distribution within the AMCs, with a significant concentration of kernel average misorientation (KAM) near the grain boundaries (GBs). In terms of micromechanical properties, the micro-zones of heterogeneous phases exhibit exceptionally high elastic modulus and nanohardness. In terms of macroscopic mechanical properties, the material exhibited impressive ultimate compressive strength and compression ratio values of 447.9 MPa and 37.9 %, respectively. These results represented a remarkable enhancement of 72.1 % and 6.6 % compared to the single FeCoNiCrMn HEA strengthening. Moreover, when applying the HEA + nano-Al2O3 blending mode, the ultimate compressive strength further increased to 506.7 MPa, representing an astonishing boost of 94.7 %. This significant strength improvement can be attributed to effective interfacial bonding, grain refinement, and a high dislocation density resulting from both HEA and Al2O3 particles.

Enhancement effects of FeCoNiCrMn high-entropy alloy doping on the Ti(C, N)-based cermets: Microstructure and mechanical properties

The enhancement effects of doping Ti(C, N)-based cermets with different contents of FeCoNiCrMn (HEA, high entropy alloy) on the mechanical properties, microstructure, cutting performance and high temperature bending strength of the Ti(C, N)-based cermets were investigated. Ti(C, N) particles had good wettability to the metal liquid phase of HEA, and with the increase of HEA content, the strength of the binder gradually improved. When the content of HEA was 12%, the cermets had the best comprehensive mechanical properties, with a relative density of 99.8%, Vickers hardness of 19.5 ± 0.2 GPa, fracture toughness of 8.2 ± 0.1 MPa·m1/2, and bending strength of 1229 ± 82 MPa. Compared with Co binders, HEA binders had better softening resistance at high temperatures. When the content of HEA exceeded 6%, the bending strength at 700 °C of the Ti(C, N)-based cermet tools were enhanced by 78%–96%, and the cutting life was increased by 35%–65%.

Effect of Sm2O3 particles on microstructure and properties of FeCoNiCrMn composite coating by laser cladding

In this work, FeCoNiCrMn high entropy alloy (HEA) coating and xSm2O3/FeCoNiCrMn (x = 0 wt%, 1 wt%, 2 wt%, 3 wt%) composite coating were prepared on the surface of 45# steel by laser cladding technology. The microstructure, phase, microhardness, wear resistance and corrosion resistance of Sm2O3/HEA composite coating were described in detail. The results show that the addition of Sm2O3 powder reduces the crack sensitivity of HEA composite coating, and the Sm2O3/HEA composite coating is mainly composed of FCC phase, Co5.24Sm0.97 phase and Fe7Sm phase. Due to the addition of Sm2O3 powder, the microstructure of the coating is refined, and the grain size is reduced. When the content of Sm2O3 is 2%, the hardness of the HEA composite coating is the highest, which is 15.85% higher than that of the HEA coating. With the increase of Sm2O3 content, the wear resistance and corrosion resistance of HEA composite coating increase first and then decrease. When the Sm2O3 content is 2%, the optimal wear resistance and corrosion resistance are achieved, and meanwhile the surface residual stress of HEA composite coating is the smallest.

The pre-corrosion fatigue behavior of 321 steel coated by laser additively manufactured FeCoNiCrMn high-entropy alloy

Corrosion caused by salt-spray and fatigue failure resulting from cyclic sea wave and strong storm are common degradation problem in offshore structural steels, and their interaction would accelerate service failure of these steels. In this work, therefore, FeCoNiCrMn high-entropy alloy (HEA) coatings were first prepared on 321 steels to simultaneously improve their corrosion and fatigue resistance. Then the pre-corrosion in salt-spray environment and subsequent high-cycle fatigue (HCF) tests were conducted on both coated and uncoated steel. The same HCF tests were also performed on the uncorroded steel specimens to reveal the influence of pre-corrosion on their fatigue resistance. The results showed that the corrosion and fatigue resistance of coated steel were both improved, which should be attributed to the higher strength, dislocation motivity and formation rate of corrosion film of the HEA coating. Moreover, pre-corrosion would decrease the mechanical properties and depth of the HEA coating, leading to significant damage to the fatigue resistance of coated steel. However, after pre-corrosion, the fatigue life of uncoated and coated steel was decreased by 18.2 %–38.8 % and 34.4 %–42.6 % at different stress amplitudes, respectively, showing the significant protective effect of HEA coatings against the pre-corrosion damage to fatigue life of offshore 321 steel.

Enhancing tensile properties of laser additive manufactured FeCoNiCrMn high entropy alloy via adding Fe-based metallic glass

It has always been difficult to significantly improve the tensile strength of FeCoNiCrMn high entropy alloy (HEA) by traditional technical methods. Here, high-strength Fe-based metallic glass (MG) was precisely selected as the strengthening phase to reinforce the mechanical properties of FeCoNiCrMn HEA fabricated by laser additive manufacturing (LAM) technology. The results showed that although the addition of Fe-based MG with 5 wt% did not change the original phase composition of HEA, it facilitated grain refinement to a great extent. Of special significance was that the strength and ductility of HEA-MG exhibited a synergistic enhancement (σy, σUTS and εf were increased by 23.8 %, 28.4 % and 31.0 %, respectively) after Fe-based MG addition, deriving from the grain refinement, increased the dislocation density and formation of deformation twins.

Significant improvement of mechanical properties of cold-spray-additive manufactured FeCoNiCrMn high-entropy alloy via post-annealing

In this work, equimolar FeCoNiCrMn high-entropy alloy (HEA) was fabricated by solid-state cold spray additive manufacturing (CSAM) technique and post-annealed. The microstructure evolution and mechanical properties of the deposits before and after annealing were systematically evaluated. The tensile test results revealed that the deposit annealed at 1000 °C for 2 h exhibited an excellent combination of tensile strength and ductility, with a doubled ultimate tensile strength of 455 MPa compared with the as-sprayed and significantly improved elongation (28%). The improved strength can be attributed to the healing of micropores and interparticle interfaces in the deposit due to the interface diffusion induced by high temperature. The recovery of ductility is the result of a significantly decreased dislocation density and enhanced metallurgical bonding at interfacial regions. For the first time, the current work demonstrated that the combination of CSAM and post-annealing strategy could achieve the strength-ductility synergy of HEA deposits. The results of in-situ analysis show that the mechanism of tensile deformation process includes particle separation, and it can be inferred that the preparation of dense sediments combined with post-treatment is the direction of further optimization.

Microstructure and properties of FeCoNiCrMn and Al2O3 hybrid particle-reinforced aluminum matrix composites fabricated by microwave sintering

In this paper, multiscale Al2O3 micro/nanoparticles (0–14 wt%) mixed with FeCoNiCrMn high-entropy alloy (HEA) particles (15 wt%) were used as reinforcements to prepare dual-phase-reinforced aluminum matrix composites (AMCs) through microwave sintering. The strengthening effects of doping different weight fractions of Al2O3 micro/nanoparticles on the microstructure, mechanical properties, and strengthening mechanisms of the mixed-phase particle-reinforced AMCs were investigated. The performance after 11 wt% Al2O3+HEA microparticles was similar to that obtained by adding 2 wt% and 5 wt% Al2O3+HEA nanoparticles. The hardness, yield strength, and compressive strength of the 2 wt% nano-Al2O3 composite were 109.7 HV, 286.5 MPa, and 506.7 MPa, respectively, which were 70.9%, 98.5%, and 94.7% higher than those of the single HEA-reinforced sample. In terms of the strengthening and toughening mechanisms, Orowan strengthening, dislocation strengthening, and thermal mismatch strengthening were the main strengthening mechanisms of particles species mixed in the metal matrix composites. Hall-Petch strengthening and load-transfer effects were mainly attributed to the cross-scale mixing of particles. The hybrid particles of HEA and Al2O3 synergistically delayed interfacial crack propagation. This study provides a new preparation method for high-performance metal matrix composites.

Evaluation of the impact of Mn and Al on the microstructure of Fe–Co–Ni–Cr based high entropy alloys

ABSTRACT In this study, an equiatomic FeCoNiCrMn high entropy alloy (HEA) was examined and compared to two Al-containing variants, FeCoNi1.5CrMnAl0.5 and FeCoNi1.5CrAl0.5, in terms of microstructure, phase composition and hardness. The vacuum cast, hot isostatically pressed (HIP’d) alloys were evaluated using differential scanning calorimetry (DSC), SEM, energy-dispersive X-ray spectroscopy (EDS), X-ray diffraction (XRD) and Vickers microhardness testing. The DSC results indicated that the solidus and liquidus temperature of the base alloy on cooling are 1296.3 and 1314.8°C, respectively. Its microstructure exhibited a single-phase face centred cubic (FCC) structure, with a small amount of σ-phase. The two Al-containing alloys (FeCoNi1.5CrMnAl0.5 and FeCoNi1.5CrAl0.5) were observed to form a secondary phase, in a FCC matrix, along the grain boundaries and within the grains. FeCoNi1.5CrMnAl0.5 had a solidus and liquidus temperature at 1271.8°C and 1287.6°C upon cooling, while FeCoNi1.5CrAl0.5 exhibited a solidus at 1354.7°C and liquidus at 1376.1°C. The hardness of the base composition was measured at 142 HV while the addition of Al and increase of Ni content in FeCoNi1.5CrMnAl0.5 increased the hardness to 202 HV and the removal of Mn in FeCoNi1.5CrAl0.5 further enhanced the hardness to 217 HV. These results aim to form a basis for understanding the effects of HEA microstructure on the material performance in oxidising environments, such as supercritical-CO2.

Process optimisation of cold spray additive manufacturing of FeCoNiCrMn high-entropy alloy

ABSTRACT The deposition window of cold spray additive manufacturing (CSAM) a high-entropy alloy (HEA) was optimised by investigating processing parameters on deposition efficiency and porosity. The optimal parameters were obtained with helium as the driving gas, gas inlet temperature was at 700°C, and spray distance at 25 mm, at which the deposit was the thickest and of the lowest porosity. The type of driving gas is critical as it affects the porosity and deposition efficiency, and helium is required to obtain high-quality HEA deposits. With it, gas inlet temperature and spray distance have a minimal effect. Furthermore, higher gas temperature and moderate spraying distance were selected to increase particle deformation and reduce the effect of shock waves at the plate front.

Enhancement of oxygen evolution reaction performance of FeCoNiCrMn high entropy alloy thin film electrodes through in-situ reconstruction

Due to the large number of defects and high entropy properties, high entropy alloy thin film electrodes prepared by magnetron sputtering are beneficial for electrocatalytic oxygen evolution reaction (OER). However, the electrocatalytic OER performance of high entropy alloy thin film electrodes without activation is limited. In this work, in-situ reconstruction (chloride corrosion) is applied to activate FeCoNiCrMn high entropy alloy thin film electrodes for promoting the electrocatalytic OER performance. The research reveals that high entropy hydroxides and high entropy (oxy)hydroxides, which are real active centers of OER electrocatalysts, are generated on the surface of FeCoNiCrMn high entropy film electrodes during in-situ reconstruction. Moreover, it is also proved that there is an obvious quantitative relationship among elements in the surface of the high entropy alloy thin film electrodes after complex chloride corrosion reaction: Ni>Mn>Fe>Co>Cr. In addition, the OER performance of FeCoNiCrMn high entropy film electrodes with in-situ reconstruction can achieve an overpotential of 263 mV and a Tafel slope of 50.9 mVdec−1. Moreover, sponge-like structures created by in situ reconstitution can help to increase surface active areas and the increased contents of high-valence elements after in situ reconstruction contribute to enhance electrocatalytic OER activity.

Enhancing hydrogen storage properties of MgH2 using FeCoNiCrMn high entropy alloy catalysts

Herein, we report the successful preparation of the FeCoNiCrMn high entropy alloy (HEA) loaded MgH2 and HEA's effect on the hydrogen storage properties of Mg/MgH2. The HEA shows high catalytic activity toward hydrogen dissociation and recombination reaction, and successfully suppressed activation energy of dehydrogenation reaction from 151.9 to 90.2 kJ mol–1. Moreover, part of Co and Ni can react with Mg, and produce Mg2Co/Mg2CoH5 and Mg2Ni/Mg2NiH4 during the hydrogen storage processes, further enhancing dehydrogenation reaction through the “hydrogen pumping” mechanism. As a result, the MgH2–5 wt% HEA composite can release 5.6 wt% of H2 at 280 °C within 10 min, and absorb 5.5 wt% H2 within 0.5 min at 150 °C. The loaded HEA shows robustness against particle aggregation, leading to stable reversible hydrogen storage processes at least 50 times. These findings show the synergistic effects of HEA on Mg-based hydrogen storage materials, providing an additional degree of freedom for catalyst design.

Novel self-supporting thin film electrodes of FeCoNiCrMn high entropy alloy for excellent oxygen evolution reaction

The characteristics of FeCoNiCrMn high entropy alloy lead to great significance in electrocatalytic oxygen evolution reaction (OER) of water splitting. However, the preparation process of high entropy alloy for OER electrocatalyst still has limitations. And thin films of metals prepared by magnetron sputtering has a large amount of defects which facilitate the formation of active sites. In this work, FeCoNiCrMn high entropy alloy self-supporting electrodes based on nickel foam were fabricated by magnetron sputtering and applied for OER. It is confirmed that there is an optimum deposition time for the best OER performance. Furthermore, the OER performance of FeCoNiCrMn high entropy alloy electrodes can be boosted by surface reconstruction through cyclic voltammetry. As is revealed by morphology and surface chemical state characterization, there are a large amount of high entropy hydroxides and oxyhydroxides formed on the surface of FeCoNiCrMn high entropy alloy electrodes after CV reconstruction. The FeCoNiCrMn high entropy alloy electrodes reconstructed by cyclic voltammetric can reach an overpotential of 282 mV and a Tafel slope of 64.3 mVdec−1.

Microbiologically influenced corrosion of FeCoNiCrMn high-entropy alloys by Pseudomonas aeruginosa biofilm.

Pseudomonas aeruginosa is widely found in industrial water and seawater. Microbiologically influenced corrosion (MIC) caused by P. aeruginosa is a serious threat and damage to the safe service of steel materials. In this study, the MIC behavior of FeCoNiCrMn high-entropy alloy (HEA) by P. aeruginosa biofilm was investigated in the simulated marine medium. The maximum pitting depth of the HEA coupons in the P. aeruginosa-inoculated medium was ~4.77 μm, which was 1.5 times that in the sterile medium. EIS and potentiodynamic polarization results indicated that P. aeruginosa biofilm reduced the corrosion resistance of the passive film of HEA coupons and promoted its anodic dissolution process. XPS and AES results further demonstrated that P. aeruginosa interfered with the distribution of elements in the passive film and significantly promoted the dissolution of Fe.

Investigation of microstructure, texture, and mechanical properties of FeCoNiCrMn high entropy alloy during drive friction welding

FeCoNiCrMn high-entropy alloy (HEA) with FCC structure was welded by continuous drive friction welding. The microstructure and mechanical properties of welding joints were investigated using OM, XRD, EBSD, TEM, microhardness, and tensile tests. The microstructure of welding joints samples consist of three zones: the weld zone (WZ), the thermal-mechanically affected zone (TMAZ) and the base metal zone (BM). The microstructure of WZ is consistent with that of BM, which is a single FCC solid solution. Discontinuous dynamic recrystallization (DDRX) and twin-induced dynamic recrystallization (TDRX) mainly occur in WZ and TMAZ. The hardness of TMAZ is significantly increased and higher than that in WZ and BM; the hardness of WZ is slightly higher than that of BM. The increase of the hardness is related to grain refinement. The tensile strength and uniform elongation of the joint samples are increased by 4.2% and 31% respectively compared with the results of the base metal. The results exhibited ductile fracture.

Microstructure and tribological properties of Al2O3 reinforced FeCoNiCrMn high entropy alloy composite coatings by cold spray

High entropy alloys (HEAs) are novel materials that have been extensively studied in recent years. In this work, Al2O3 particles reinforced FeCoNiCrMn HEA composite coatings were fabricated by cold spray. The microstructure, mechanical and tribological properties of the composites coating were studied and compared with those of the pure FeCoNiCrMn coating. The results indicate that cold spray is a promising process to fabricate HEA composite coatings. The composite coatings made in this work had higher hardness than pure FeCoNiCrMn coating due to the reinforcing effect of well distributed Al2O3 particles. The composite coatings also had improved wear-resistance properties with nearly 50% reduction in wear rate as compared to the pure FeCoNiCrMn coating. The improvement was due to the formation of tribo-layer which can effectively withstand material loss. The results also reveal that the main wear mechanisms for the composite coatings were dominated by adhesive wear in comparison to abrasive wear for the pure FeCoNiCrMn coating. This study proves the feasibility of cold spray for the fabrication of high-performance HEA composite coatings.

Enhanced wearing resistance of carbide reinforced FeCoNiCrMn high entropy alloy prepared by mechanical alloying and spark plasma sintering

Aiming to improve the wearing resistance of high entropy alloys (HEAs), this work prepared carbide reinforced FeCoNiCrMn HEA composites using mechanical alloying (MA) and spark plasma sintering (SPS) methods. The multiple carbides were introduced into the HEAs in two ways using in situ hydrocarbon additives in the MA process (HECin) and ex situ carbide additives (HECex) as carbon resources, respectively. The HECin consisted of HEA solid solution and embedded carbides of M23C6 and M7C3, leading to yield strength (YS) 1756 MPa and maximum compressive strain (MCS) 10.28%, ~14.5% stronger than the reported HEAs prepared via MA and SPS processing. The HECex introduced additional 5 wt% TaC and TiC, leading to YS 1760 MPa and MCS 7.85%. Compared with the HECin, the HECex increased hardness by ~40% (from 7.44 GPa to 9.47 GPa), but decreased friction coefficients by ~18% (from 0.32 to 0.26). The microstructure analysis of worn surface show that the HECin had adhesive wearing and slight oxidation wearing while the HECex had mainly oxidation wearing with slight adhesive wearing and fatigue wearing. This work demonstrated that the carbide reinforced HEA has superior wearing resistance properties compared with the pristine HEA and can be adopted as an effective hard coating materials.

Fabrication of Fe-based metallic glass reinforced FeCoNiCrMn high-entropy alloy through additive manufacturing: mechanical property enhancement and corrosion resistance improvement

In recent years, high entropy alloys (HEA) receive extensive attention for their excellent mechanical performance. In this paper, the FeCoNiCrMn high-entropy alloy reinforced material is produced by laser powder bed fusion (LPBF). The excellent tensile performance can be achieved through many strengthening mechanisms, e.g., solution strengthening, dislocation strengthening, fine-grain refinement, and dispersion strengthening. The reinforced material with additive Fe-based metallic glass shows a yield strength of 675 MPa, 29.8% higher than FeCoNiCrMn (520 MPa), and an average hardness of 241.9 HV, 12.7% higher than FeCoNiCrMn (214.6 HV). Meanwhile, the plasticity of the reinforced material is maintained at a good level. In comparison with FeCoNiCrMn, the corrosion current density is reduced by 18.9%, and the corrosion resistance is significantly improved. The high strength and corrosion resistance are achieved by the addition of Fe-based metallic glass, which provides a feasible approach for the preparation of HEA with enhanced mechanical properties in the future.

Effect of Mo addition on structures and properties of FeCoNiCrMn high entropy alloy film by direct current magnetron sputtering

FeCoNiCrMnMox high-entropy alloy (HEA) films were prepared by direct current (DC) magnetron co-sputtering. The influence of the Mo content on the microstructures and mechanical properties of the HEA films were systematically studied by X-ray diffraction (XRD), field emission scanning electron microscope (FESEM), Vickers hardness test and tribological test. The addition of Mo results in the formation of a denser film with refined grain size, and promotes the transformation from a face-centered cubic (FCC) phase to a mixture of FCC and body-centered cubic (BCC) phases. The hardness of the films increases from 8.5 GPa (x = 0) to 12 GPa (x = 1) and the friction coefficient decreases from 0.5 (x = 0) to 0.3 (x = 1), which greatly enhance the damage tolerance of the film. The improved mechanical and tribological properties of the HEA films are attributed to the formation of the hard BCC phase and grain refinement at high contents of Mo. The FeCoNiCrMnMox HEA films are suitable candidates for structural application as protective coatings.

Dislocation-driven high catalytic performance of FeCoNiCrMn high-entropy alloy for the hydrolysis of NaBH4

A high-entropy alloy Fe10Co10Ni10Cr10Mn60 ribbon catalyst with a face-centered cubic structure was designed by using Co and Ni as the main catalytic elements and combining various co-catalytic elements, such as Fe, Mn, and Cr. Substantial element selective corrosion occurs during the acid solution corrosion process, which induces the exposure of many Co and Ni atoms, increases the specific surface area, and further results in the formation of many vacancies and dislocations. This unique structure generates a positive electron effect, that is the peaks of Ni2p3/2 and Co2p3/2 shift to lower binding energies, namely, approximately 1 eV for Ni and 0.8 eV for Co, indicating the Co and Ni enrich electrons. The catalyst shows an excellent catalytic performance for the hydrolysis of NaBH4 after corrosion for 90 s, whose hydrogen production rate approaches 18.46 l/(m2·min). This work opens up a direction for the application of the macroscopic scale high-entropy alloy in the catalytic hydrogen field.

Microstructure and mechanical properties of a laser welded Ti–6Al–4V titanium alloy/FeCoNiCrMn high entropy alloy with a Cu filler layer

A high-power solid-state laser was used to weld the Ti–6Al–4V titanium alloy and the FeCoNiCrMn high-entropy alloy. By adding a pure Cu filler layer for the laser welding, a strong welded joint is obtained and the average tensile strength of the laser welded Ti–6Al–4V/FeCoNiCrMn joint exceeds 140 MPa. Composition and mechanical properties of phases in the laser welded Ti–6Al–4V/FeCoNiCrMn joint were investigated by the optical microscope, the electron probe microanalysis technique, the scanning electron microscope and the nanoindentation technique. The fusion zone is mainly composed of the Cu-rich and the FeCoNiCrMn-rich regions. The Cu-rich phases can disperse brittle intermetallic compounds such as Ti–Fe, to prevent the formation of a continuous brittle compound layer, thereby improving the plasticity of the welded joint and promoting the formation of the joint. The temperature distribution model in the fusion zone was established, and combined with the element distribution and phase composition analysis results in the fusion zone, microstructure mechanism for formation of the fusion zone was proposed.