CrFeCoNi High Entropy Alloy Research Articles

Effect of nitric acid concentration on corrosion behavior of CrFeCoNi high entropy alloy

CrFeCoNi high entropy alloy (HEA) was prepared by the method of vacuum melting. Its corrosion behavior in HNO3 solution with different concentrations was studied. The electrochemical test results indicated that the corrosion resistance firstly increased with increasing HNO3 concentration from 0.1 M to 4 M, and then decreased with further increasing HNO3 concentration to 6 M. The CrFeCoNi HEA exhibited the best corrosion resistance in 4 M HNO3 solution. The discrepancy of corrosion property in different concentration of HNO3 solutions could be attributed to the different protection of passive film formed on HEA. XPS results indicated that the content of Cr2O3 in the passive film initially increased with increasing HNO3 concentration from 0.1 M to 4 M, and then decreased with further increasing HNO3 concentration to 6 M. Higher content of Cr2O3 in the passive film was responsible for better corrosion property.

Atomistic simulations of tensile properties and deformation mechanisms in a gradient nanostructured Al0.3CrFeCoNi high-entropy alloy

Atomistic simulations of tensile properties and deformation mechanisms in a gradient nanostructured Al0.3CrFeCoNi high-entropy alloy

Chemical environment effects on the size of mono-vacancy in CrFeCoNi alloy

Atomic studies of mono-vacancy are crucial for comprehending the mechanisms governing the related macroscopic properties of materials. High-entropy alloys (HEAs) manifest unique properties arising from a complex, localized, disordered chemical environment and distinctive site lattice distortions. In this study, the effects of chemical environment on the size of vacancy point defects in equiatomic CrFeCoNi alloy are investigated using Density Functional Theory through positron annihilation lifetime (PL) calculations. To better understand the nature of local lattice distortion, a similar atomic environment method is employed for supercell construction. Our findings reveal a significant inverse relationship between the PL of single-vacancy in CrFeCoNi HEA and the number of its first nearest neighbor Cr atoms. The underlying mechanisms in the perspective of local atomic mismatch and electronic structures are discussed.

Effect of transition-metals (Fe, Co and Ni) on the L12-phase strengthening in the Al0.3CrFeCoNi high-entropy alloy

L12-strengthened high-entropy alloys have become research of interest for their great potential to achieve a superb balance between ductility and strength. While much attention has been paid to strong L12-phase forming elements, little discussion has focused on the role of transition-metals. The concentration of Fe, Co, and Cr in the Al0.3CrFeCoNi alloy was decreased to investigate how transition-metals affect the stability and distribution of the L12 precipitate. The transmission electron microscope was used to characterize the precipitation behavior in the four alloys. The results show that reducing the level of transition-metals promotes the stability of the L12 phase. In the case of the base Al0.3CrFeCoNi alloy, B2 phase replaces nanosized L12 particles as the main precipitates when aging at 700 °C. In contrast, uniformly dispersed L12 nanoparticles remain stable after 700 °C aging, with almost no B2 phase observed. Adjusting the content of these transition-metals can also alter the solid solubility of Al in the fcc matrix and change the site occupancy of Al sites in the L12 phase, enabling a shift in the volume percentage of the L12 phase. Of the three elements tested, Fe reduction effectively increases the fraction of the L12 phase, while Cr reduction even have a little negative influence on the density of the L12 particles. As a result, the microhardness and strength decrease in the following sequence: Al0.3CrFe0·6CoNi1.4, Al0.3CrFeCo0·6Ni1.4, Al0.3CrFeCoNi and Al0.3Cr0·6FeCoNi1.4. This study provides significant insights into the role of transition-metals and facilitates the design of L12-strengthened high-entropy alloys with excellent mechanical properties.

Effect of Heat Treatment on Microstructure of Silicon-containing CrFeCoNi High Entropy Alloys Produced by Low-Pressure Plasma Spraying

Effect of Heat Treatment on Microstructure of Silicon-containing CrFeCoNi High Entropy Alloys Produced by Low-Pressure Plasma Spraying

Surprising cocktail effect in high entropy alloys on catalyzing magnesium hydride for solid-state hydrogen storage

Magnesium hydride (MgH2) attracts wide interests as a promising hydrogen energy carrier, but its commercial application is hampered by the high operating temperatures and slow dehydrogenation kinetics. Herein, CrMnFeCoNi and CrFeCoNi high-entropy alloys (HEAs) were adopted to boost the hydrogen storage performance of MgH2. It was demonstrated that the morphology of catalysts and addition of Mn had a great impact on the performance of HEAs catalysts. In particular, the Mn containing HEAs nanosheets presented the best performance. The MgH2-CrMnFeCoNi composite could release 6.5 wt% H2 in 10 min at 300 °C and started to absorb H2 at 40 °C. Moreover, kinetic analysis revealed that the rate control model in dehydrogenation process of HEA-4 modified MgH2 changed from permeation model of MgH2 to diffusion. In addition, 97% hydrogen storage volume could be maintained after 20 cycles at 300 °C, showing a good cycling performance. Microstructure analysis showed that the CrMnFeCoNi nanosheets were uniform dispersed over the surface of MgH2, bringing numerous heterogeneous activation sites to speed up the dispersal of hydrogen. Besides, the cocktail effect of HEAs exerted synergic action between Cr, Mn, Fe, Co and Ni elements to improve the overall catalytic efficiency. Therefore, the de/rehydrogeantion performance of the MgH2-CrMnFeCoNi composite was surprisingly accelerated.

A superior strength-ductility synergy of Al0.1CrFeCoNi high-entropy alloy with fully recrystallized ultrafine grains and annealing twins

• Giant strengthening in Al 0.1 CrFeCoNi by cold rolling and short-time annealing. • Al 0.1 CrFeCoNi possesses yield strength of 885 MPa and uniform elongation of 23.4%. • Ultrafine-grained structure and multiple deformation twins lead to high strength. Grain refinement usually makes the materials stronger, while ductility has a dramatic loss. Here, a superior tensile strength–ductility synergy in a fully recrystallized ultrafine-grained (UFG) Al 0.1 CrFeCoNi with abundant annealing twins was achieved by cold rolling at room temperature and short-time annealing. The microstructure characterization using electron backscattered scattering diffraction demonstrates that abundant geometrically necessary dislocations (GNDs) gather around the grain boundaries and twin boundaries after tensile deformation. Although coarse-grained (CG) samples undergo a larger plastic deformation than UFG samples, the GND density decreases with grain size ranging from UFG to CG. Transmission electron microscopy results reveal that the annealing twin boundary, which effectively hinders the dislocation slip and stores dislocation in grain interior, and the activation of multiple deformation twins are responsible for the superior strength–ductility synergy and work hardening ability. In addition, the yield strength of fully recrystallized Al 0.1 CrFeCoNi follows a Hall–Petch relationship ( σ y = 24 + 676 d –1/2 ), where d takes into account both grain boundaries and annealing twin boundaries. The strengthening effects of grain boundaries and annealing twin boundaries were also evaluated separately.

Effects of Fe on L12 phase precipitation and mechanical properties in Al0.3CrFeCoNi high-entropy alloy

The newly developed L12-strengthened high-entropy alloy shows great potential to possess superior combinations of physical and mechanical properties. It has been extensively studied how to control the L12 phase by adjusting L12-phase forming elements such as Al, Ti, Ta and Nb. However, the effect of transition-metal elements on L12 precipitation is still unclear. This work investigated the effect of Fe on the stability and distribution of the L12 phase by reducing the level of Fe in a well-studied high-entropy alloy Al0.3CrFeCoNi. A close examination of the precipitation behaviour in the Al0.3CrFeCoNi and Al0.3CrFe0.6CoNi1.4 alloys was conducted using transmission electron microscopes. When the aging temperature reaches 700 °C in the Al0.3CrFeCoNi alloy, nanosized L12 particles would transition to the B2 phase. By reducing the amount of Fe, the stability and density of the L12 phase were both enhanced. After 700 °C annealing, L12 nanoparticles are still stable in the Al0.3CrFe0.6CoNi1.4 alloy and there is no evidence of B2 phase precipitation. Less Fe can lower the concentration of Al in both the fcc and L12 phases during aging at a lower temperature of 620 °C when the L12 phase in both alloys is stable. A lower Fe concentration can also lead to more Cr and Fe atoms occupying Al sites in the L12 phase, which can result in the formation of more L12 particles. Since more L12 particles were precipitated when the amount of Fe was reduced, the Al0.3CrFe0.6CoNi1.4 alloy exhibits better strength and higher hardness than the Al0.3CrFeCoNi alloy. These findings give us insight into how transition metals affect the behaviour of L12 precipitation and suggest ways to develop and improve L12-strengthened HEAs.

Study on the deformation mechanism of the Al0.1CrFeCoNi high entropy alloy at different deformation degrees under electric pulse treatment

In this study, electrical pulses were used as a treatment to investigate the role played by dislocations in the deformation mechanism of the Al0.1CrFeCoNi high-entropy alloy (HEA) at different stages of deformation. The results demonstrated that the HEA was completely deformed through dislocation slip during compression, and no twins were evident. Under the action of Electric pulse treatment (EPT), the specimen expanded thermally owing to Joule heating. Additionally, the pulse current accelerated the movement of the dislocations and led to dislocation annihilation, softening the material without changing the grain shape. However, further application of EPT with the same parameters failed to produce significant changes in the dislocation density, a phenomenon that has rarely been reported before. Our results provide strong theoretical and technical support for the rapid annealing of metallic materials during processing and the use of HEA in electrical structural components, such as wear-resistant coatings or parts resistant to galvanic corrosion.

First-principle study of interstitial atoms (C, B and Si) in CrFeCoNi high entropy alloy

The incorporation of nonmetallic elements in alloys is one of the major approaches to tailor properties. In this paper, first-principles methods are employed to investigate the effect of interstitial C, B and Si in CrFeCoNi high entropy alloys (HEAs). The four local environments around interstitial atom, i.e., Cr-rich, Fe-rich, Co-rich and Ni-rich have the close formation energy for each interstitial atom. The bond length between the interstitial atom and alloying component suggests the severe lattice distortion occurs, even in Si doped case. Whereas the local magnetic moments of Ni are not affected by the interstitial atoms.

High temperature tensile and creep properties of CrMnFeCoNi and CrFeCoNi high-entropy alloys

High temperature tensile and creep properties of face-centered cubic (FCC) high-entropy alloys (HEAs), CrMnFeCoNi and CrFeCoNi, were evaluated at 500–700 and 650–725 °C, respectively, to evaluate high temperature structural integrity of the most well-known FCC HEAs with special attention on (i) sigma phase formation in CrMnFeCoNi and (ii) difference in solid solution strengthening between the two alloys in the temperature range where commercial heat-resistant wrought alloys including austenitic heat-resistant steels and Ni-based superalloys are used. No remarkable difference was detected in tensile behavior measured both at room and high temperatures between the two alloys. However, creep rupture life turned out to be significantly longer for the CrFeCoNi quaternary alloy. On top of the longer creep rupture life, CrFeCoNi alloy is characterized by lower minimum creep rate and larger creep activation barrier energy which could be attributed to higher level of lattice distortion of CrFeCoNi than CrMnFeCoNi resulting in higher solid solution strengthening. Also, grain boundary strength of CrMnFeCoNi was compromised by the formation of sigma phase during creep deformation which led to lower elongation especially for long-term creep conditions. Therefore, the longer creep life of CrFeCoNi is mainly attributed to the combination of enhanced solid solution strengthening and stronger grain boundary which is free from the deleterious sigma phase due to the reduced thermodynamic driving force for formation of intermetallic phase.

Effects of Fe on L12 Phase Precipitation in Al0.3crfeconi High-Entropy Alloy

Effects of Fe on L12 Phase Precipitation in Al0.3crfeconi High-Entropy Alloy

Temperature-dependent hardening contributions in CrFeCoNi high-entropy alloy

We studied the deformation behavior of CrFeCoNi high-entropy alloy by in situ neutron diffraction at room temperature, intermediate low temperature of 140 K, low temperatures of 40 K (no serrated deformation) and 25 K (with massive serrations). The evolution of lattice strain and texture along different grain orientations provided distinct insights into deformation behavior at low temperatures. The in situ data showed an early activation of stacking faults and a higher stacking fault probability with decreasing test temperature. The stacking fault probability reached ∼4.7% at low temperatures. The dislocation density at 40 and 25 K evolved similarly and had a very high value of ∼9.2 × 1015 m−2. However, twin fault probability at 25 K (∼6%) was higher than that at 40 K (∼5%). The samples at 40 and 25 K deformed uniformly and lacked any necking region, thus imparting an excellent ductility of ∼58%. The contributions from different deformation mechanisms to the yield strength and strain hardening have been estimated. The athermal contributions to the yield strength were ∼183 MPa at all temperatures, while the Peierls stress increased significantly at low temperatures (from 148 MPa at room temperature to 493 MPa at 25 K). Dislocations contributed to ∼94% strain hardening at room temperature. Although the dislocation strengthening remained the major hardening mechanism at very low temperatures, the planar faults contribution increased steadily from 6% at room temperature to 28% at 25 K.

Phase and structural changes during heat treatment of additive manufactured CrFeCoNi high-entropy alloy

Additive manufacturing (AM) of high-entropy alloys (HEAs) is a new challenge in the Material Science and Advanced Manufacturing fields. In the AM processing procedure, heat treatments after fabrication are often beneficial to stabilize microstructure and properties, while limited reports are available for AM HEAs. In the current study, the effect of a post-printing heat treatment at 400–1000 ℃ for 24 h and for 21 days on the changes in structures and phase compositions of an AM CrFeCoNi alloy prepared by the laser powder bed fusion AM technique is presented to better understand a heat treatment-microstructure-property relationship of the AM HEA. Heating up to 600 ℃ demonstrated the polygonization process in the alloy. Grain growth was observed in the alloy upon heating over 700 ℃, while a preferred texture is observed along the build direction after annealing at 900 ℃ for 24 h. The formation of the secondary phase was revealed, and it is associated with the impurities of the initial CrFeCoNi powder. The AM CrFeCoNi system demonstrates excellent phase stability inthe solid solution for all annealing temperatures.

Improved Tribocorrosion Resistance by Addition of Sn to CrFeCoNi High Entropy Alloy

Among the high entropy or complex concentrated alloys (HEAs/CCAs), one type of system is commonly based on CoCrFeNi, which as an equiatomic quaternary alloy that forms a single phase FCC structure. In this work, the effect of Sn in an equiatomic quinary system with CoCrFeNi is shown to lead to a great improvement in hardness and resistance to tribocorrosion. The addition causes a phase transition from a single FCC phase in CoCrFeNi to dual phase in CoCrFeNiSn with an Ni-Sn intermetallic phase, and a CoCrFeNi FCC phase. The presence of both the hard intermetallic and this ductile phase helps to resist crack propagation, and consequent material removal during wear. In addition, the high polarization resistance of the passive film formed at the surface and the high corrosion potential of the Ni-Sn phase contribute to preventing chloride corrosion attack during corrosion testing. This film is tenacious enough for the effect to persist under tribocorrosion conditions.

Improving high-temperature mechanical properties of cast CrFeCoNi high-entropy alloy by highly thermostable in-situ precipitated carbides

The CrFeCoNi high-entropy alloy (HEA) exhibits excellent mechanical properties at lower temperatures due to its low stacking-fault energy, however, its medium- and high-temperature strengths are still insufficient. In consideration of the potential diversified applications, more strengthening approaches except for the previously proposed L12 phase hardening deserve further exploration due to its rapid coarsening tendency at high temperatures. Here, we achieved significant high-temperature strengthening of the cast CrFeCoNi HEA by in-situ precipitation of highly thermostable carbides. Alloys with 0.5 at.% and 1 at.% niobium and carbon were prepared by simple casting processes, i.e. drop cast, solute solution and aging. A highly thermostable microstructure was formed, which comprises very coarse grains accompanied with extensive thermostable carbide precipitates embedded, including submicrometer coherent NbC particles in grain interiors and intergranular coherent M23C6 carbides. This high thermostability of microstructure, which is beneficial for the high-temperature loading, is ascribed to the synergy of lacking growth driving force and Zenner pinning effect by the carbides. Tensile properties tested at 673, 873 and 1073 K show that the yield strength and ultimate tensile strength are significantly increased by Nb/C doping, along with the elongation escalation at higher temperatures. The strengthening is mainly due to the precipitation hardening of carbide particles.

Notch-tensile behavior of Al0.1CrFeCoNi high entropy alloy

Notch-tensile behavior of an Al0.1CrFeCoNi high entropy alloy (Al0.1-HEA) was studied using V-notch geometry and with local strain mapping using digital image correlation (DIC). A notch-strength ratio of 1.51 indicated notch strengthening. Further analysis of stress-strain response supplemented with microstructural analysis revealed that, while the presence of notch results in strengthening due to work hardening by twinning induced plasticity, the notch also contributes strongly to geometrical softening in the non-uniform ductility regime, and accounts for the onset of failure. The strain localization behavior of Al0.1-HEA due to the presence of V-notch was compared with three conventional alloys: Inconel 625 nickel-based superalloy, 304 stainless steel and Ti–6Al–4V titanium alloy. The study revealed that the nature of notch widening with increasing strain was dependent on material characteristics. The extent of notch widening impacted the local strain field and stress distribution, thereby influencing the propensity for crack initiation and growth. The experimental results were verified by finite element analysis.

The influence of incorporation of Mn on the pitting corrosion performance of CrFeCoNi High Entropy Alloy at different temperatures

The electrochemical behavior and susceptibility to pitting corrosion of CrFeCoNi and CrMnFeCoNi high entropy alloys were studied in a 0.1 M NaCl solution at temperatures ranging from 25 to 75 °C. Electrochemical measurements revealed that CrMnFeCoNi is more susceptible to oxide film breakdown and localized corrosion compared to CrFeCoNi. Post corrosion microscopic observations showed severe pitting corrosion for CrMnFeCoNi in higher temperatures compared to CrFeCoNi. Based on in-depth XPS profile measurements on the remaining oxide films, this behavior was attributed to the depletion of Cr in the oxide film and detrimental presence of Mn in the matrix solid solution of CrMnFeCoNi.

Vanishing of room-temperature slip avalanches in a face-centered-cubic high-entropy alloy by ultrafine grain formation

High-pressure torsion (HPT) was applied to Al0.3CrFeCoNi high-entropy alloy to study the effect of severe grain-refinement on the deformation behavior. After 10 rotations of HPT, the grain size was reduced to tens of nanometers. Nano-twins and stacking faults were found in the nano-grained samples. This nano-grain formation led to an obvious increase in micro-Vickers hardness, and vanishing of slip avalanches during nanoindentation which was evidenced by the absence of pop-ins in the loading segment. These phenomena can be attributed to the affluent grain boundaries that acted as extra mediators for plastic deformation and obstacles for the propagation of lattice dislocations.

The Role of Carbon in Grain Refinement of Cast CrFeCoNi High-Entropy Alloys

As a promising engineering material, high-entropy alloys (HEAs) CrFeCoNi system has attracted extensive attention worldwide. Their cast alloys are of great importance because of their great formability of complex components, which can be further improved through the transition of the columnar to equiaxed grains and grain refinement. In the current work, the influence of C contents on the grain structures and mechanical properties of the as-cast high-entropy alloy CrFeCoNi was chosen as the target and systematically studied via a hybrid approach of the experiments and thermodynamic calculations. The alloys with various C additions were prepared by arc melting and drop cast. The as-cast macrostructure and microstructure were characterized using optical microscopy, scanning electron microscopy, and transmission electron microscopy. The cast HEAs transform from coarse columnar grains into equiaxed grains with the C level increased to ≥ 2 at. pct and the size of equiaxed grains is further decreased with the increasing C addition. It is revealed that the interdendritic segregation of Cr and C results in grain boundary precipitation of M23C6 carbides. The grain refinement is attributed to the additional constitutional supercoiling from the C addition. The yield stress and tensile strength at room temperature are improved due to the transition of columnar to equiaxed grains and grain refinement.