Fe50Mn30Co10Cr10 High-entropy Alloy Research Articles

Optimizing laser cladding process parameters for transformation-induced plasticity FeMnCoCr high entropy alloy: A multi-objective approach

A multi-objective optimization approach utilizing the response surface method (RSM) is proposed to determine the optimal processing parameters for laser cladding of Fe50Mn30Co10Cr10 coating. In this paper, a single-variable control method was employed to adjust the laser cladding parameters, and preliminary experiments were conducted to establish the optimization range for the RSM laser cladding parameters. A mathematical prediction model of input processing parameters (laser power, scanning speed and powder feed speed) and output response (dilution rate, W/H, microhardness and porosity) was established by the response surface method. The results indicated that both the dilution rate and microhardness had a positive correlation with laser power and scanning speed, while they were negatively correlated with the powder feed rate. The scanning speed is the most significant factor influencing the porosity of the coating, followed by the powder feed rate. The optimal processing parameters were identified as follows: laser power at 1750 W, scanning speed at 8.0 mm/s, and powder feed rate at 11.5 g/min. The model demonstrated strong agreement with the experimental results. The coating molding quality is exceptional, with an average porosity of 0.07 % and an average microhardness of 208.32 HV0.2. Meanwhile, the coating was composed of HCP phase and FCC phase, with the HCP phase comprising15.6 % and the FCC phase 84.4 %, respectively. Under the optimal processing parameters, the Fe50Mn30Co10Cr10 high-entropy alloy coating demonstrated impressive ductility and strength, with a deformation of 55.93 % and a compressive strength of 2153.7 MPa. The fracture mechanism of Fe50Mn30Co10Cr10 coatings is transcrystalline fracture and toughness fractures.

Metastability-driven room temperature strain hardening in a nitrogen added FeMnCoCrN high-entropy alloy

This study deals with the strain hardening capability of a nitrogen added FeMnCoCr high-entropy alloy during room temperature tensile deformation with an emphasize on the mechanical stability of FCC phase. The heightened metastability of the FCC phase provides a proper condition for hierarchical evolution of dual-phase FCC-HCP structure which finally promotes the formation of 63% HCP martensite. Initially favoring slip mechanisms, the texture of the FCC phase transitions to geometrically hard orientations, thereby reducing its deformation accommodation capacity. This transition prompts the involvement of the HCP phase, initially evidenced by the emergence of new FCC phase and ε-twins at HCP martensite intersections. Subsequently, the formation of thickened ε-twins within the primary HCP lathes further contributes to deformation accommodation, explaining the observed excellent hardening behavior in the as-cast structure.

Temperature dependence of corrosion behavior of a dual-phase Fe50Mn30Co10Cr10 high entropy alloy in supercritical water at 380–650 °C

Corrosion behavior of a dual-phase Fe50Mn30Co10Cr10 HEA subjected to supercritical water at different temperatures was investigated. Both weight gain and oxide film thickness increased with increasing temperatures. An outer layer with polyhedral MnFe2O4 particles and an inner layer containing a mixture of CrMn1.5O4 and Fe3O4 were formed at 380 °C. Mn2O3 outer and CrMn1.5O4 inner layers developed at 550 and 650 °C, but the loose granular Mn2O3 particles at 550 °C transformed into a compact oxide film at 650 °C. Besides, Cr2O3 oxide particles were observed along the grain boundaries. The corrosion mechanism at different temperatures was also discussed.

Effects of rolling at different temperatures and subsequent recovery annealing on the mechanical properties of a metastable carbon containing FeMnCoCr high-entropy alloy

Metallic materials or alloys consisting of single face-cubic centered (FCC) phases typically face difficulties in obtaining high strength without sacrificing ductility. The introduction of different crystalline defects via pre-straining and the activation of multiple deformation mechanisms have been shown to be effective in achieving superior strength–ductility synergy. In this work, we investigated the role of varying rolling conditions and subsequent annealing on the mechanical response in an established twinning- and transformation-induced plasticity dual phase high-entropy alloy (TWIP-TRIP-DP HEA). We found that all of the annealed samples exhibited similar nano-twinned structures. Furthermore, phase transformation from FCC γ to hexagonal close-packed (HCP) ε prevailed along the nano-twins under mechanical loading. With increasing rolling temperature, the phase stability of the matrix revealed a downward trend, resulting in a significant increase in TWIP/TRIP effects along with a prominent change in the deformation microstructure. Our study presented a simple and feasible strategy for manipulating mechanical performance by modulating the microstructural characteristics and associated deformation modes.

Effect of deep cryogenic treatment on microstructure and mechanical properties of Fe50Mn30Co10Cr10 high entropy alloy fabricated by laser metal deposition

As a typical additive manufacturing technology, laser metal deposition (LMD) has been widely used to process high entropy alloy (HEA). However, deposited products usually have poor mechanical properties. In this study, deep cryogenic treatment (DCT) is proposed to enhance the mechanical performance of the laser melting deposited Fe50Mn30Co10Cr10 high entropy alloy. The tensile strength, hardness and strength-plasticity product of the HEA after 48 h of immersion by DCT processing were 901 MPa, 286HV and 33.3 GPa%, respectively. Compared with the as-deposited state, the HCP ε phase content and tensile strength of the deep cryogenic treated (DCTed) sample increased by 2.2 times and 30.8 %, respectively, while the average grain size decreased by 58.0 %. Furthermore, the friction coefficient and wear rate of the DCTed samples reduced by 25.6 % and 30.3 %, respectively. The high temperature gradient soaking in liquid nitrogen induced dynamic recrystallization, refining the FCC γ grain structures in the HEA. Meanwhile, the samples contained more HCP ε phase due to the transformation-induced plasticity (TRIP) effect triggered by thermal stress. The results indicate that the effects of fine-grain strengthening and second-phase particle dispersion strengthening contribute to the excellent mechanical performance. DCT processing provides a simple and effective way for overcoming the strength-ductility trade-off in the additive manufactured Fe50Mn30Co10Cr10 HEA.

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.