Fe50Mn30Co10Cr10 High-entropy Alloy Research Articles

Cooperative roles of twinning, transformation and strain partitioning on the excellent cryogenic strength-toughness synergy of dual-heterogeneous metastable high entropy alloys

In a metastable Fe50Mn30Co10Cr10 high entropy alloy (HEA), a dual-heterogeneous structure, encompassing both grain size and dislocation heterogeneity, has been constructed to obtain excellent cryogenic mechanical performance by varying the annealing temperature (630 and 740 °C) following severe deformation. The HS-630 sample, consisting of recovered coarse-grains (CG), recrystallized fine-grains (FGs) and un-recrystallized ultrafine-grains (UFGs), possesses higher yield strength (YS) of ∼965 MPa, ultimate tensile strength (UTS) of ∼1680 MPa and uniform elongation (UEL) of ∼45 % when compared to the fully-recrystallized HS-740 sample at liquid nitrogen temperature (LNT). The difference in YS is primarily caused by the grain boundary and dislocation strengthening of UFGs, whereas the higher ductility of the HS-630 sample is associated with the hierarchical activation of transformation- and twinning-induced plasticity (TRIP and TWIP) effects, and compatible strain partitioning between heterogeneous domains. The dual-heterogeneity results in different critical stresses of ε-phase nucleation in heterogeneous domains, and promotes sustainable TRIP effect in CGs and the emergence of TWIP effect in UFGs with strain progressing. Moreover, the strain of the ductile transformed ε-phase is mainly accommodated by non-basal slip, which contributes to the strain hardening in the later deformation stage. Furthermore, the higher cryogenic impact toughness of the HS-630 sample can be attributed to the synergistic effects of the fracture mode, the transformation characteristics, and the heterogeneous strain partitioning.

Improving tensile and impact properties of Fe50Mn30Co10Cr10 high entropy alloy via microstructural engineering

This study investigates the Fe50Mn30Co10Cr10 high entropy alloy (HEA), featuring a dual-phase structure with face-centered cubic (FCC) and hexagonal close-packed (HCP) phases, in both cast and forged states. The cast samples exhibited an average tensile strength of 675.9 MPa and an elongation at break of 34 %, while the forged samples showed superior properties with a strength of 821.0 MPa and 50 % elongation. Impact tests at room temperature, 200 K, and 77 K revealed that forged samples consistently had higher impact energy (144 J, 119 J, and 109 J, respectively) compared to cast samples (99 J, 80 J, and 66 J). This research underscores the significant influence of the dual-phase structure and fabrication process on the mechanical and impact properties of the Fe50Mn30Co10Cr10 system HEAs.

Superior mechanical properties and multiple strengthening mechanisms of a V-alloyed FeMnCoCr high-entropy alloy

The FeMnCoCr-based high-entropy alloys (HEAs) have attracted much attention owing to their great potential to be used as engineering materials. Yet, due to the dominant face-centered cubic (FCC) structure, yield strength of those alloys is usually low, which limits their practical applications. In this study, we propose a method of obtaining the superior strength and ductility combination of the FeMnCoCr HEAs via V alloying combined with a simple processing route including cold rolling and partial recrystallization annealing. Yield strength of the partially recrystallized Fe50Mn25Co10Cr10V5 material reaches 900 MPa, which is 80 % higher than that of the Fe50Mn30Co10Cr10 alloy fabricated by the same processing route. Meanwhile, a uniform elongation of 17.7 % is maintained. These are attributed to the introduction of the second phase with the body-centered cubic (BCC) structure via V addition together with the improved strengthening by grain boundaries, dislocations and solid solution, while the transformation induced plasticity (TRIP) effect is still maintained during deformation. Additionally, the partial recrystallization annealing process also inhibits nucleation and growth of the hard and brittle σ phase in the Fe50Mn25Co10Cr10V5 alloy, making the uniform elongation reach more than three times that of the fully recrystallized material, while the yield strength is only 51 MPa lower than that of the latter. This study provides new insights for the design and development of advanced metallic materials with high performances.

Effect of abnormal grain refinement on synchronous strengthening behavior of Fe50Mn30Co10Cr10 high entropy alloys

Improving processing efficiency while obtaining excellent material formation and mechanical properties is the primary concern of the manufacturing industry. This study aims to refine the grains of Fe50Mn30Co10Cr10 high entropy alloy during friction stir processing, achieving exceptional tensile properties in the stir zone by increasing the rotational speed. The key driver behind grain refinement lies in the alloy's inherently low stacking fault energy, with the primary recrystallization mechanism being discontinuous dynamic recrystallization. The freshly recrystallized fine grains share analogous microstructures and energy levels during severe plastic deformation, which engenders a state of increased competition among them. This robust competitive dynamic impedes grain growth, thereby promoting the development of refined grains. This microstructure proves instrumental in avoiding premature microcracking during tensile loading by hindering martensite formation, consequently improving the UTS and EL of the material. Nevertheless, the high heat input and substantial strain result in an increase of temperature and strain energy in the system, eventually disrupting the high energy system and causing grain coarsening as the rotational speed continues to increase. This coarsened grain and high martensite fraction lead to premature initiation of cracks under tensile loading, which is not conducive to further improvement of tensile properties.

Sensitivity of reduction rate on the mechanical response of boron-doped Fe50Mn30Co10Cr10 high entropy alloy

Phase transformation induced plasticity (TRIP) effect is an effective technical solution to enhance the strength and ductility of alloys, represented by Fe50Mn30Co10Cr10 high entropy alloy (HEA). Introducing heterostructures into alloys is also an effective synergistic method for enhancing the strength and ductility of alloys. Combining element doping, heterostructures, and the TRIP effect of the alloy itself can enable the alloy to achieve both high strength and high ductility. In this work, the boron doped Fe50Mn30Co10Cr10 HEA were prepared by cold rolling with different reduction rates followed by recrystallization annealing processes. Different reduction rates result in different heterogeneous structures. The large rolling reduction weakens the advantage of heterogeneous structure for introducing large stress concentration, resulting in the low ductility of the alloy. The sample with small rolling reduction shows excellent strength and ductility, which comes from the synergistic effect of large-small grains matching and TRIP effect. In summary, the TRIP effect combined with the appropriate amount of reduction and low recrystallization temperature annealing induced heterostructure is an effective solution to overcome the strength ductility trade-off.

Enhancing the strength-ductility synergy in hot-forged Fe50Mn30Co10Cr10 high entropy alloy (HEA) through carbon additions

In this work, we systematically investigated the effect of carbon additions on the microstructure and room temperature mechanical properties of hot-forged Fe50Mn30Co10Cr10 HEA. The different carbon contents were introduced to Fe50-xMn30Co10Cr10Cx (x = 1, 2.5, 6 at.%, hereinafter, referred as C1, C2.5 and C6, respectively) HEAs to enhance the strength-ductility synergy by triggering the multiple strengthening mechanisms. The results showed that the grain sizes were decreased with increasing of carbon content, while a high fraction of mechanical twins ∼45% were generated in C2.5 HEA, and their fractions were ∼35% in C1 and C6 HEAs. Moreover, the discrete nano-sized M23C6 carbides in C2.5 HEA were transformed into continuous mico-sized M23C6 carbides along the grain boundaries in C6 HEA. Therefore, C2.5 HEA possessed high yield strength of 584 MPa, tensile strength of 1.03 GPa and outstanding ductility of 68%, i-e., breaking the strength-ductility paradox. A highest yield strength of∼662 MPa and tensile strength of more than 1 GPa were observed for C6HEA with refine grains, although the ductility was only ∼10%, which indicated that the massive carbon addition could effectively enhanced the strength of HEA but at the cost of ductility due to the presence of coarse M23C6 carbide precipitation. The enhanced mechanical properties of studied HEAs are mainly ascribed to the contribution of multiple strengthening mechanisms including precipitation, grain boundary, dislocation and interstitial solid solution strengthening.

Effects of WC–10Co4Cr and TiC additions on microstructure and tribological properties of laser cladded FeMnCoCr HEA coatings

FeMnCoCr high–entropy alloy (HEA), FeMnCoCr HEA–10%(WC–10Co4Cr) and −10%TiC coatings were fabricated by laser cladding. The effects of WC–10Co4Cr and TiC on the microstructure, phases and hardness of obtained coatings were analyzed via a super depth field microscope, X–ray diffraction, and microhardness tester, respectively. The tribological properties of obtained coatings at 500 °C were investigated using a ball–on–disc wear tester, and the wear mechanism was discussed in detail. The results show that the hardness of FeMnCoCr HEA coating is increased by the WC–10Co4Cr and TiC additions, which is attributed to the solid solution strengthening effects of WC and TiC. The wear rates of FeMnCoCr HEA–10%(WC–10Co4Cr) and −10%TiC coatings are decreased compared with the FeMnCoCr HEA coating by 65.47 % and 75.58 %, respectively, showing that the TiC has better strengthening effect than the WC. After the friction test, the worn track of FeMnCoCr HEA–10%TiC coating is composed of CoSiO4, MnFeO4 and FeCr2O4 phases, which forms the oxide film to prevent the wear loss of coating. The wear mechanism of FeMnCoCr HEA coating is adhesive wear and oxidative wear, accompanied with abrasive wear; while those of FeMnCoCr HEA–10%(WC–10Co4Cr) and −10%TiC coatings are abrasive wear, adhesive wear and oxidative wear.

Microstructure and mechanical properties of Fe50Mn30Co10Cr10 high-entropy alloy with Si addition prepared by laser melting deposition

Microstructure and mechanical properties of Fe50Mn30Co10Cr10 high-entropy alloy with Si addition prepared by laser melting deposition

NbC reinforced FeMnCoCr high entropy alloy with excellent mechanical properties and wear resistance

In this paper, a NbC reinforced FeMnCoCr dual-phase high entropy alloy was used. After hot rolling, cold rolling and annealing, partial recrystallization sample and fully recrystallized fine-grained sample were obtained. The annealed samples are a single FCC phase, with micron-sized NbC particles of different shapes including columnar, granular and polygonal are distributed in the matrix. The yield strength of the partial recrystallization sample is 708 MPa, which was 1.4 times of the yield strength of the fine-grained sample, and the tensile elongation is 39.4%. The main reasons for the high yield strength of partially recrystallized samples is dislocation strengthening. The recrystallization volume fraction of partially recrystallized samples is 66.2%, and the un-recrystallization grains contain high dislocation density, and the increment of dislocation strengthening is 144 MPa. The work hardening rate of partially recrystallized samples is lower than that of fine-grained samples. Due to the high dislocation density in the partially recrystallized samples, there are fewer dislocations that can be activated and propagated during the tensile process. The high yield strength and the existence of a large number of micron-sized NbC make the NbC reinforced FeMnCoCr high entropy alloy have good wear resistance.

Microstructure evolution and mechanical properties of friction stir welded Fe50Mn30Co10Cr10 high-entropy alloy

Metastable Fe50Mn30Co10Cr10 HEA has a significant strength-ductility synergistic effect and a wide application prospect in nuclear power. The present work reports the microstructure evolution and tensile behavior of friction stir-welded joints for Fe50Mn30Co10Cr10 high entropy alloy (HEA) at various rotational speeds. Defect-free welds of Fe50Mn30Co10Cr10 alloy were obtained by a W-Re alloy welding tool. Significant grain refinement occurs in the nugget zone, where the most of HCP phases in the base metal transformed into FCC phase. Additionally, strain-induced Σ3 mechanical twins are generated in the FCC austenite grains. The microstructure of thermo-mechanically affected zone exhibited multiple deformation mechanisms, including stacking faults, martensite lath, martensite variants, and reverse transformation. The microhardness of the joint primarily depends on the grain size of the FCC phase and the fraction of twins and HCP phase. In the nugget zone of the joint welded at 300 rpm, a high microhardness zone ranging from 266.7 to 310 HV was detected. While the reverse transformation and fresh twinning in the joint at 600 rpm contribute to the enhancement of tensile properties, the increase in grain size and ε martensitic fraction have resulted in a noteworthy reduction in ultimate tensile strength (UTS) and elongation (EL). Conversely, the joint of 300 rpm exhibited optimum UTS and EL owing to the grain refining after FSW and the transformation induced plasticity (TRIP) effect. These insights confirm that FSW is an ideal approach for achieving superior joint performance in dual-phase HEAs.

Cu alloying enables superior strength-ductility combination and high corrosion resistance of FeMnCoCr high entropy alloy

The metastable dual phase FeMnCoCr high entropy alloy (HEA) has attracted great attention since it was first proposed, as it can overcome the strength-ductility trade-off at room temperature. For materials in engineering applications, it is also important to achieve high corrosion resistance while maintaining good mechanical properties. In this study, we simultaneously improved the mechanical properties and corrosion resistance of a FeMnCoCr-based HEA via Cu alloying and by applying a simple processing route that combined cold rolling and partial recrystallization annealing. The alloy doped with 0.3 at.% Cu and processed by annealing at 650 °C for 3 min exhibited the best combination of strength and ductility, i.e., yield strength of 768 MPa, tensile strength of 960 MPa and uniform elongation of 33.6%. The high yield strength majorly originated from high density dislocations and grain boundaries in the material, while the formation of deformation twins, martensite laths, stacking faults and Lomer Cottrell locks contributed to the continuous strain hardening and good ductility. The addition of Cu also enhanced corrosion resistance of the HEA in a NaCl solution by improving stability of the alloy matrix and elevating compactness of the passive film. The solid solution of Cu elevated equilibrium potential of the matrix and promotes transformation of microstructure from the face-centered cubic (fcc) plus hexagonal close-packed (hcp) dual phases to the fcc single phase, effectively inhibiting the accelerated corrosion of micro galvanic couple between different phases and enhancing stability of the matrix. At the same time, the enrichment of CuO in the inner layer of the passive film reduced the defect density within the Fe-rich oxide layer, improving the protection of the passive film against the matrix.

Metastable FeCrMnCo HEAs with the reinforcement of tungsten carbide fabricated by laser melting: Microstructure, mechanical properties and tribological behaviors

Fe50Mn30Co10Cr10 high entropy alloy (HEA) can be considered as a candidate structural and functional material, but the early failure during friction with heavy load can limit its more extensive applications. In this paper, a series of tungsten carbide particle reinforced Fe50Mn30Co10Cr10 HEAs were fabricated by laser cladding technique, the influence of tungsten carbide content on microstructure, mechanical properties and tribological behaviors were explored systematically. The results indicated that the dissolution and diffusion of tungsten carbide could contribute to a wettability between tungsten carbide and HEA matrix, and grain refinement was caused by increasing tungsten carbide. The UTS and EL of the P10 sample are increased by simultaneously by 26.8% and 31.1% compared with UTS of 696 MPa and EL of 15.1% for P5 sample. UTS and EL were enhanced simultaneously owing to fine-grained strengthening and nanoscale precipitate strengthening. But higher content of tungsten carbide could cause lower elongation owing to the embrittlement of the materials. Just as this, Rockwell hardness and friction coefficient has an increasing trend with increasing tungsten carbide when an opposite trend exists in volume wear rate. It can indicate that hardness is a more important factor for wear resistance, and excellent wear resistance with 1.25 × 10−5 mm3/(N·m) appear in higher-content WCp reinforced HEA composite. Furthermore, wear mechanism is transformed from abrasive wear in low-content tungsten carbide to adhesive wear in high-content tungsten carbide.

Significantly enhancing elevated-temperature strength and ductility of a FeMnCoCr high-entropy alloy via grain boundary engineering: Exploring multi-deformation mechanisms

The objective of the study is to elucidate the influence of grain boundary engineering (GBE) on the high-temperature properties of a metastable FeMnCoCr high-entropy alloy (HEA). Using thermo-mechanical processing (TMP), the grain boundary character distribution (GBCD) was optimized, which involved the increase of coincidence site lattice (CSL) special boundaries and multiple twinning events, and breaking of random high-angle grain boundaries (RHAGBs) network. Furthermore, the deformation strain of the alloy became more uniform at high temperature, dynamic recrystallization was suppressed, and a number of deformation mechanisms were operative. The ductility of studied HEA was significantly enhanced by over 200% at 1073 K, resulting in a remarkable 1.35-fold increase.

Evolution of microstructure and mechanical properties in gas tungsten arc welded dual-phase Fe50Mn30Co10Cr10 high entropy alloy

In recent years, high entropy alloys (HEAs) have been shown to be promising alternatives to common engineering alloys, depending on their composition and thermomechanical processing. Up to now, several works aimed at improving the mechanical properties and discovering different HEAs given the extremely large compositional possibilities made available by the multicomponent approach associated to these materials. Their processability, however, is an important topic that must be studied. Welding is a key manufacturing technique that will eventually be applied to HEAs. Thus, there is a need to evaluate the microstructure and property changes induced by the weld thermal cycles, to assess the suitability of certain welding process/HEAs combinations for possible industrial applications. In the present work, Gas Tungsten Arc Welding (GTAW) was used to achieve defect-free joints based on a novel transformation induced plasticity (TRIP) Fe50Mn30Co10Cr10 HEA. The microstructure and mechanical behavior of the joints were assessed by means of optical and electron microscopy, synchrotron X-ray diffraction, thermodynamical calculations, microhardness mapping and tensile testing. Overall, an excellent mechanical performance was obtained on the resulting joints, opening the door for their adoption in real-life applications.

Substructure development, martensitic transformation and rapid work-hardening in an as-cast interstitial substituted N atom in FeMnCoCr high-entropy alloy

The microstructural evolution and room-temperature mechanical properties of nitrogen-added Fe50Mn30Co10Cr10 as-cast high-entropy alloy were investigated. Interestingly, an excellent strength-ductility trade-off with a rapid hardening stage was achieved in the as-cast structure (tensile strength: 740 MPa, ductility: 42 %) that was comparable with those counterparts holding wrought structure. These excellent mechanical properties were attributed to the capability of metastable FCC microstructure enabling deformation-induced martensitic transformation even at low imposed strain at room temperature. Simultaneously, the occurrence of substructure development independent of martensitic transformation, significantly contribute to increase the capability of the material for strain accommodation.

Bidirectional transformation enabled improvement in strength and ductility of metastable Fe50Mn30Co10Cr10 complex concentrated alloy under dynamic deformation

High strain rate compression experiments performed on a non-equiatomic metastable fcc + hcp Fe50Mn30Co10Cr10 high entropy alloy using split Hopkinson pressure bar setup shows improved flow stress and compression ductility compared to quasistatic deformed samples. The deformation response was characterised by the occurrence of hardening and softening stages compared to sustained strain hardening for quasistatic deformation. Detailed EBSD, BSE imaging analysis coupled with TEM shows significant bi-directional transformation (B-TRIP) and increased fcc γ phase stability in high strain rate regime while only forward (fcc to hcp) transformation dominates with increasing fraction of hcp ε phase in the quasistatic regime of deformation. Bidirectional transformation aided by adiabatic heating and heterogeneous deformation in the high strain rate regime leads to optimal stress and strain partitioning between the two phases and delays the initiation of damage at the interface. The presence of concomitant strain rate hardening and improvement in ductility in the dynamic deformation regime opens up avenues for microstructural tunability to achieve simultaneous improvement in strength and ductility using the metastability paradigm in complex concentrated alloys.

Microstructure and tensile properties of metastable Fe50Mn30Co10Cr10 high-entropy alloy prepared via powder metallurgy

With the characterization of microstructure and tensile properties, the feasibility of preparing Fe50Mn30Co10Cr10 high-entropy alloys (HEAs) via powder metallurgy was explored, and the effect of sintering temperature and deformation temperature on the microstructure and tensile properties of the alloy was investigated. The alloys sintered at different temperatures possessed a dual-phase structure with face-centered cubic (FCC) and hexagonal close-packed (HCP). The average grain size, HCP phase fraction, and twinning boundary fraction increased with the sintering temperature. The best combination of strength and ductility was obtained in the alloy sintered at 1000 °C, which exhibited a strongly temperature-dependent mechanical behavior, i.e., when the deformation temperature decreased from 298 to 77 K, the yield strength and ultimate tensile strength increased from ∼287 to ∼490 MPa and from ∼745 to ∼1107 MPa, respectively, with only a tiny loss of uniform elongation; this is mainly attributed to the deformation mode of the alloy varied with deformation temperature. During tensile deformation at 298 K, dislocation slip, phase transformation, detwinning of annealing twins, and mechanical twinning were the dominant mechanisms, while no mechanical twinning was activated at 77 K. The excellent combination of strength and ductility for the alloy at 77 K relative to 298 K is mainly attributed to a more significant TRIP effect. Powder metallurgy can be used as a promising way for manufacturing metastable high entropy alloys with excellent tensile properties.

Enhanced strength-ductility synergy in NbC-reinforced FeMnCoCr high entropy alloy with heterostructure by adopting a novel process

We explored a novel heterostructure design strategy to simultaneously enhance the strength and ductility of NbC-reinforced FeMnCoCr high-entropy alloys by adopting grain-scale strain localization regulation coupling partial recrystallization annealing, and the effect of cold-rolled microstructure on annealed microstructure evolution and mechanical properties was studied. The transformation-induced plasticity (TRIP) effect and the dislocation density decreased as the grain size increased. The significant grain-scale strain localization and obvious Brass and A textures were observed in the cold-rolled microstructure of the large grain samples. Recrystallization preferentially occurred in the high-strain region during annealing leading to heterogeneous recrystallization nucleation. The recrystallization kinetics of A texture was slow and remained in the partially recrystallized microstructure. A heterostructure with a bimodal grain size distribution was formed in coarse-grained samples. The heterostructure with coarse un-recrystallized grains wrapped by recrystallized grains has good comprehensive mechanical properties. Its yield strength was 1.4 times that of a fine-grained microstructure sample, while maintaining excellent strain hardening capacity without decreasing elongation. The high yield strength was attributed to dislocation strengthening. The TRIP effect appeared earlier in the coarse un-recrystallized grains with low dislocation density under tension, and the back stress strengthening and TRIP effect improved the strain hardening capacity.

Microstructures, Mechanical and High-Temperature Tribological Properties of Dual-Phase Fe50Mn30Co10Cr10 High-Entropy Alloy Fabricated by Laser Metal Deposition

Microstructures, Mechanical and High-Temperature Tribological Properties of Dual-Phase Fe50Mn30Co10Cr10 High-Entropy Alloy Fabricated by Laser Metal Deposition

Atomistic simulations of martensitic transformation processes for metastable FeMnCoCr high-entropy alloy

Atomistic simulations of martensitic transformation processes for metastable FeMnCoCr high-entropy alloy