FeCoCrNiMn High-entropy Alloy Research Articles

Oxidation corrosion wear and lubricating mechanisms of WC particles reinforced FeCoCrNiMn high - entropy alloys coatings

The FeCoCrNiMn high-entropy alloy coating reinforced with WC particles was fabricated on 45# steel using plasma surfacing technique. A comprehensive characterization was conducted to investigate the friction and wear behavior of the coating at various temperatures. Results demonstrated that this coating exhibited exceptional wear resistance at room temperature (RT). However, it experienced slight decomposition of WC particles and oxidation corrosion at 400 °C, resulting in a degradation of its wear resistance. The WC decomposition and oxidation corrosion were aggravated at 600 °C, inducing a stronger oxidation corrosion wear effect, and thus led to a more severe wear of this coating. However, these oxidation products provided considerable lubrication effect resulting in a continuous decrease in friction coefficient, from 0.49 at RT to 0.44 at 400 °C, and reached a lower value of 0.16 at 600 °C. The potential oxidation corrosion wear and lubricating mechanisms of this coating at evaluated temperatures were discussed systematically.

Evolution of interfacial phases between Al alloy and high entropy alloy during annealing

While the interfacial phases between Al and high-entropy alloy (HEA) share the same types as that between Al and steel, it has been found previously that the thermal stability of the Al-HEA interfacial phases is significantly higher than that of the Al-steel interfacial phases. To further elucidate the reason for the exceptional thermal stability of Al-HEA interfacial phases, this study investigated the evolution of the interfacial phases formed between Al alloy and FeCoCrNiMn HEA during annealing. An Al-FeCoCrNiMn thin film diffusion couple was extracted from a friction stir lap welding (FSLW) joint by focused ion beam and then annealed at 400 °C. An amorphous layer is formed initially at the interface due to the high strain rate deformation during FSLW. The amorphous layer remained even after prolonged annealing at 400 °C (∼0.72 Tm of Al alloy) for 60 min with very limited thickening (from 50 nm to 55 nm), showing remarkable thermal stability at the relatively high temperature. Al13Fe4-type intermetallic compound (IMC) with the Fe site occupied by Fe, Co, Cr, Ni and Mn first nucleates at the interface between Al alloy and amorphous layer. With the annealing time extended to 180 min, the amorphous layer is partially transformed into Al5Fe2-type IMC. The rate constant for the thickening of the reaction layer at the Al/FeCoCrNiMn interface is 0.03 μm∙min1/2, which is much smaller than (only 0.02 times) that at the Al/steel interface under similar annealing condition. The high thermal stability of Al-HEA interfacial layer is thus attributed to the slow kinetics in crystallization of the initially formed amorphous layer, the barrier effect of amorphous layer for interdiffusion, and the reduced diffusivity inside of IMCs caused by significant fluctuations in lattice potential energy due to high-density doping with HEA elements. This finding provides new insights into the fabrication of thermally stable Al-HEA hybrid structures suitable for service conditions involving high-temperature exposure.

Structural Evolution and Fracture Mechanism of WC-Particle-Reinforced FeCoCrNiMn High-Entropy Alloy Coatings

A hard-particle-reinforced high-entropy alloy (HEA) coating shows significant potential for tribological applications, but relatively little work on the fracture mechanism of the coating has been reported. In this work, the FeCoCrNiMn HEA coatings, doped with varying contents of WC, were fabricated using a plasma surfacing technique. The structure, mechanical properties, and fracture behaviors of these coatings were investigated through X-ray diffraction (XRD), scanning electron microscopy (SEM), and hardness and tensile tests. The addition of WC particles significantly altered the growth mode of the coating texture from large coarse grains to fine grains. The coating without WC doping had a hardness of 198.8 ± 15.6 HV, a yield strength of 225 MPa, a tensile strength of 478 MPa, and a strain of 53.7%. The hardness, yield strength, tensile strength, and strain were 222.3 ± 34.4 HV, 353 MPa, 704 MPa, and 42.6% for the coating with 10% WC doping and 355.6 ± 51.6 HV, 454 MPa, 627 MPa, and 9.4% for the coating with 20% WC doping. Meanwhile, the coating with 40% WC doping showed the greatest hardness of 514.9 ± 48.1 HV and had the highest yield strength of 457 MPa, but its tensile strength and strain decreased to 517 MPa and 2.7%, respectively. In this article, the detailed structural evolution, strengthening, and fracture failure mechanisms of the coatings are discussed systematically.

Effect of Ti and C addition on oxidation resistance of FeCoCrNiMn high entropy alloys prepared by powder metallurgy

Purpose The purpose of this paper is to study the high temperature oxidation behavior of Ti and C-added FeCoCrNiMn high entropy alloys (HEAs). Design/methodology/approach Cyclic oxidation method was used to obtain the oxidation kinetic profile and oxidation rate. The microstructures of the surface and cross section of the samples after oxidation were characterized by X-ray diffraction (XRD) and scanning electron microscope (SEM). Findings The results show that the microstructure of the alloy mainly consisted of FCC (Face-centered Cubic Structure) main phase and carbides (M7C3, M23C6 and TiC). With the increase of Ti and C content, the microhardness, strength and oxidation resistance of the alloy were effectively improved. After oxidation at a constant temperature of 800 °C for 100 h, the preferential oxidation of chromium in the chromium carbide determined the early formation of dense chromium oxide layers compared to the HEAs substrate, resulting in the optimal oxidation resistance of the TC30 alloy. Originality/value More precipitated CrC can preferentially oxidize and rapidly form a dense Cr2O3 layer early in the oxidation, which will slow down the further oxidation of the alloy.

Understanding the Fracture Failure Mechanism of WC Particle-Reinforced FeCoCrNiMn High-Entropy Alloy Coatings at 600 °C

Understanding the Fracture Failure Mechanism of WC Particle-Reinforced FeCoCrNiMn High-Entropy Alloy Coatings at 600 °C

Influence of Cold Rolling on the Microstructure and Mechanical Properties of FeCoCrNiMn High-Entropy Alloy

Influence of Cold Rolling on the Microstructure and Mechanical Properties of FeCoCrNiMn High-Entropy Alloy

Effect of TiC addition on the microstructure and mechanical properties of FeCoCrNiMn high entropy alloy fabricated by selective laser melting

FeCoCrNiMn high entropy alloy (HEA) has attracted significant interest due to its exceptional properties at both room and cryogenic temperatures; however, its relatively low yield strength limits its practical engineering applications. In this study, FeCoCrNiMn HEA composites with various TiC contents were manufactured using selective laser melting, and the effect of TiC content on their microstructures and mechanical properties was investigated. The results indicated that an energy density of 150 J/mm3 is adequate for achieving an optimal relative density of 99.0%. The TiC particles were uniformly distributed along the cellular boundaries of the FeCoCrNiMn matrix, contributing to grain refinement and significantly enhancing strength. Notably, HEA composites with 5 wt% TiC demonstrated an impressive combination of high yield strength of 725.8 MPa and excellent notch fracture toughness of 81.0 MPa·m1/2, presenting their substantial potential for engineering applications. Both experimental analysis and theoretical predictions suggested that the additional strength provided by TiC addition is mainly attributed to grain refinement, dislocation entanglement, and dispersion strengthening.

Effect of ZrC on the Microstructure and Properties of CrMnFeCoNi High-Entropy Alloy Coatings Prepared by a Plasma Transferred Arc Process

The low strength caused by the single FCC structure of the CrMnFeCoNi high entropy alloy (HEA) limits its application in the field of coating. Here, we prepared high-entropy alloy coatings of CrMnFeCoNi with different ZrC contents on Q235 steel by a plasma transferred arc process. The effects of ZrC on the microstructure and properties of the CrMnFeCoNi HEA coating were investigated by optical microscopy, scanning electron microscope, and X-ray diffraction and by employing a potensiostat/galvanostat. The results showed that ZrC mainly existed in the coatings as a second phase, having little influence on the main crystal structure and micromorphology of the CrMnFeCoNi HEA coating. The hardness of the CrMnFeCoNi HEA coating increased with the ZrC content. ZrC can effectively improve the corrosion resistance of the CrMnFeCoNi HEA coating. In a 1 mol/L NaCl solution with 4 wt% ZrC, the annual corrosion rate was only 5.997% of that of the HEA coating. Nevertheless, the improvement in the wear resistance of CrMnFeCoNi high-entropy alloy coatings was not apparent with the addition of ZrC. Consequently, the addition of ZrC to the FeCoCrNiMn high-entropy alloy coating holds promise for applications in corrosion resistance, particularly in oceanic environments.

Study of tribological property of laser-cladded FeCoCrNiMnx high-entropy alloy coatings via experiment and molecular dynamics simulation

Laser cladding was used to fabricate the high entropy alloy (HEA) coating of FeCoCrNiMnx (x = 0, 0.5, 1). Coatings were studied to determine how Mn affected the microstructure, microhardness, and tribological property. Molecular dynamics simulations were used to examine the atomic-scale deformation and wear behavior of FeCoCrNiMn HEA coatings. FeCoCrNiMnx HEA coatings were composed of single FCC-type solid solution. Friction reduction and wear resistance are improved with Mn doping. When compared to the substrate and FeCoCrNi coating, the wear resistance of Mn1 coating is superior by 69.34% and 25.05%, respectively (wear rate is 3.74 ×10−5 mm3/N·m). The findings of molecular dynamics simulations demonstrate that Mn-doping significantly enhances strain hardening by the friction-induced FCC phase transition to the HCP phase. The deformation mechanism of Mn1 coating, as determined by the dislocation evolution pattern, is twinning induced plasticity, which improves the plasticity, strength, and work-hardening rate of coating all at once.

Effect of annealing treatments on microstructure, tensile and wear properties of cold-rolled FeCoCrNiMn high entropy alloy

The equiatomic FeCoCrNiMn is a highly studied high-entropy alloy (HEA) known for its exceptional properties. In this study, FeCoCrNiMn HEAs with varying grain sizes were prepared by heavy cold rolling and subsequent annealing at 900 °C for different durations. Ultrafine-grained sample with an average grain size of about 0.75 μm was obtained after annealing for 2 min, which displayed an enhanced strength-ductility combination with a yield strength of around 620 MPa, an ultimate strength of around 778 and a tensile elongation of over 30 %. Grain boundary strengthening contributed significantly to the mechanical strength of the resulting alloy. The grain size of the alloy increased with annealing times, aligning well with the linear Hall-Petch relationship, and the processed HEA demonstrated the expected strength-ductility trade-off. The ultrafine-grained sample exhibited improved wear performance with reduced wear rate and improved worn surface characteristics compared to the coarser-grained samples. The wear mechanism of the FeCoCrNiMn alloy primarily involved abrasive wear and oxidative wear.

The Influence of Ball Milling Time and Sintering Temperature on the Structural and Capabilities of FeCoCrNiMn High-Entropy Alloy

This study reports the fabrication of FeCoCrNiMn high-entropy alloy using high-purity powders of Fe, Co, Cr, Ni, and Mn through the processes of mechanical alloying (MA) and spark plasma sintering (SPS). We systematically investigated the effects of different ball milling times (10 h, 20 h, 30 h, 40 h, 50 h) and sintering temperatures (700°C, 800°C, 900°C, 1000°C, 1100°C) on the structure and capabilities of the alloy. The findings indicate that the atomic proportion of Fe:Co:Cr:Ni:Mn approach 1:1:1:1:1. The distribution of all elements is basically uniform, but the Cr element is slightly biased in the structure after 40 h ball milling. The voids in the structure are gradually decreasing as temperatures rise. The matrix structure is mainly composed of a white FCC matrix phase and a gray Cr-rich σ phase. The alloy structure is the densest. It has the highest density of 7.060 g/cm3, the highest compressive strength of 1480 MPa, and a plastic deformation of 13% when the SPS temperature reaches 1000°C. The FeCoCrNiMn high-entropy alloy is prepared by a ball milling time of 40 h, and spark plasma sintering of 1000°C has the best comprehensive properties.

Study on the FeCoCrNiMnTix High Entropy Alloys Fabricated by Laser Cladding

Because of the high entropy effect, a simple solid solution structure can be obtained in high entropy alloys (HEAs), giving the HEAs greater overall properties than conventional alloys. Cladding layers of FeCoCrNiMnTix HEAs were prepared on Q355 steel by laser cladding technology. X-ray diffraction (XRD), metallographic microscope (OM), and scanning electron microscope (SEM) were used to examine the microstructure of the cladding layers. The microhardness and wear resistance were tested using a Vickers microhardness tester and wear testing machine, respectively. The FeCoCrNiMn HEAs consisted of a face-centered cubic (FCC) solid solution. The addition of Ti promoted the formation of body-centered cubic (BCC) and hexagonal solid solution. When Ti content was higher than x=0.8, the Laves phase formed. The addition of Ti increased the microhardness of the FeCoCrNiMnTix (x=0.5, 0.6, 0.8, 1.0) HEAs, which is due to the effect of solution strengthening, microstructure strengthening, and grain refinement. When Ti content was less than x=0.6, the alloy’s wear resistance was positively correlated with its hardness, and the Ti0.6 alloy had the best wear resistance. However, as Ti content exceeded x=0.6, the brittle and hard Laves phase formed, which resulted in reduced wear resistance.

Super capacity of boron on the grain refinement of FeCoCrNiMn high entropy alloy

Super capacity of boron on the grain refinement of FeCoCrNiMn high entropy alloy

Enhancement of grain boundary carburization of FeCoCrNiMn high-entropy alloy coating by supersonic fine particle bombarding and rare earth

A new strategy to simultaneously introduce the supersonic fine particle bombarding (SFPB) and rare earth was proposed in this work. By using the coupling effect of grain refinement and rare earth catalysis, the grain boundary carburization of the FeCoCrNiMn high-entropy alloy (HEA) coating was synergistically enhanced. With increasing content of rare earth, the gray phase of grain boundary was completely strengthened, and the black phase enriched in C increased and refined uniformly. The strengthened coating was composed of FCC phase and M7C3 phase with an orientation relationship of [3, − 1, − 2, − 5] ∥ [1, 1, 0]. Compared with the untreated coating and the single carburized coating, the hardness of the strengthened coating was increased by 1.46 times and 0.33 times, respectively, and the residual compressive stress increased by 31.44 times and 1.80 times, respectively. The research results can provide new methods for strengthening the HEA coatings.

Improved passivation ability via tuning dislocation cell substructures for FeCoCrNiMn high-entropy alloy fabricated by laser powder bed fusion

Elemental-decorated dislocation cell is a specific substructure in additively manufactured metals and alloys due to the intrinsic layer-by-layer rapid melting and solidification process, and the novel cellular structures would have significant influences on the service performances of the printed components. In this work, sub-micro Mn-decorated dislocation cells are verified in FeCoCrNiMn high-entropy alloys (HEAs) fabricated via laser powder bed fusion (L-PBF), and the related passivation capabilities are comparably investigated with the as-casted and heat-treated L-PBF counterparts (HEA-800, 800 °C for 2 h). The passive current density of L-PBF HEA-800 is the lowest in borate buffer solutions, while the as-casted HEAs show the highest corrosion rate therein. The high-density dislocation and the alleviation of Mn segregation at the cellular boundaries are conducive to the superior protectiveness (stable and thick passive film) for L-PBF HEA-800 and the underlying mechanisms for different passivation behaviors are discussed.

Precipitation behaviors and mechanical properties of a cold-rolled equiatomic FeCoCrNiMn high entropy alloy after long-time annealing treatment at 500 °C

The thermodynamic stability of extensively investigated equiatomic FeCoCrNiMn high entropy alloy has been doubted in recent investigations. In this study, we conducted a long-time annealing treatment on a cold-rolled FeCoCrNiMn alloy at 500 ℃ with the time from 240 to 960 h. The results show that three phases precipitated after a long-time annealing treatment at 500 ℃. The precipitation sequence of these phases starts with two phases (a Cr-rich phase and a NiMn-rich phase) at annealing time ranging from 240 to 720 h, followed by a third FeCo-rich phase at a longer annealing period of 960 h. Besides, the long-time annealing treatment at 500 ℃ results in partial recrystallization of the cold-rolled alloy. The formation of the precipitation affects significantly the mechanical properties of the alloy, including hardness, yield strength and also the ductility.

Microstructure and mechanical properties of friction stir lap welds between FeCoCrNiMn high entropy alloy and 6061 Al alloy

To investigate the microstructure and mechanical properties of the dissimilar joint between high entropy alloys (HEAs) and Al alloy, FeCoCrNiMn was joined to 6061 Al alloy by friction stir lap welding (FSLW) at tool rotation speeds from 900 rpm to 1800 rpm. Systematic tilting high-resolution transmission electron microscopy patterns were applied to study the interfacial microstructure. A nanoscale (< 250 nm) interfacial layer was found at the 6061/FeCoCrNiMn interface and the phase formed in this layer was identified as Al13Fe4-type intermetallic compound (IMC) with the Fe-sites occupied by HEA elements. Microsegregation of HEA elements was observed in this Al13Fe4-type IMC in two different modes: 1) co-segregation of Cr and Mn and co-depletion of Co and Ni, for the majority of the interfacial layer, and 2) co-segregation of Co and Ni and co-depletion of Cr and Mn, mainly in regions adjacent to the Al alloy side and sporadic in the middle. The maximum tensile lap shear strength reached 151 MPa, which was approximately 73 % of the shear strength of 6061 base material. The joint fracture occurred within Al alloy nearby the interface rather than right along the interfacial layer, suggesting high interfacial metallurgical bonding achieved in this study.

Effect of Si content and annealing temperatures on microstructure, tensile properties of FeCoCrNiMn high entropy alloys

In the present study, FeCoCrNiMnSix (x = 0, 0.1, and 0.2, molar ratio) high-entropy alloys (HEAs) were prepared via arc melting, and subsequently deformed via cold rolling and annealing (CRA). The effects of Si content and annealing temperature on the microstructural evolution and tensile properties of the alloys were systematically investigated. The results indicate that a single-phase FCC structure of coarse-grained FeCoCrNiMnSix HEAs was obtained after homogenized annealing (HOA), and the distribution of each element was uniform. When the molar ratio of Si was increased from 0 to 0.2, the strength of the HOA HEAs increased by nearly 50%, and the elongation did not decrease, largely due to solid solution strengthening and the reduction in stacking fault energy. Conversely, as Si content increased, the recrystallization ratio decreased during annealing. A heterogeneous grain structure composed of recrystallized and residual deformation regions (high density of dislocations and deformation twinning) was obtained by changing the CRA temperature and Si content. A heterogeneous grain structure of CRA HEAs with an annealing temperature of 700 ℃ and Si content of 0.2 exhibits approximately fourfold higher yield strength (733 MPa) compared to that of HOA FeCoCrNiMn HEAs (185.27 MPa). The structure’s tensile strength and ductility were measured at 959 MPa and 29.5%, respectively. The high strength was mainly attributed to the combined effect of multiple strengthening mechanisms. Heterogeneous deformation-induced strain hardening and twinning-induced plasticity provide good ductility.

Investigation on high entropy alloys as interconnect material for intermediate temperature solid oxide fuel cells

Investigation of Solid Oxide Fuel Cells (SOFCs) is receiving great attention due to its higher efficiency and zero environmental pollution during operation. Interconnects are a critical part of the SOFC stack which connects the cells in series and combines the electricity produced. The present study aims to investigate High Entropy Alloys (HEAs) for interconnect application in intermediate temperature SOFC. Towards this, FeCoCrNi, FeCoCrNiMn0.1, FeCoCrNiMn0.5, and FeCoCrNiMn HEAs are prepared by vacuum arc melting and examined for its phase evaluation. Thermal stability, thermal expansion, resistivity, oxidation, and Area Specific Resistance (ASR) are investigated up to 800 °C. Oxidation studies show the formation of multicomponent oxide in the HEAs which suppresses the growth of Cr2O3 layer. FeCoCrNiMn0.1, FeCoCrNiMn0.5, and FeCoCrNiMn HEAs possess ASR values less than 100 mΩ.cm2 in the temperature range of 600–800 °C which ensure the superior performance of the SOFC stack.

Cyclic behavior of FeCoCrNiMn high entropy alloy coatings produced through cold spray

FeCoCrNiMn high entropy alloy powders were employed to produce coatings on carbon steel through high pressure cold spray (at 1100 °C and 7 MPa in temperature and pressure respectively). X-ray diffraction of the sprayed material revealed a dense coating with the retention of the original crystallographic structure. Once splatted, particles revealed high flattening ratio with consequent excellent adhesion of the coating to the substrate. Residual stresses and hardness increased through the thickness of the coating. The cyclic behavior of the coatings was evaluated through bending tests. The cyclic bending tests were performed by linearly increase the maximum deformation at a fixed number of loading cycles. Other bending tests were conducted at fixed maximum stroke at the same deformation levels indicated for the previous test up to the coating fracture. For ach 100 cycles the test was stopped in order to observe the coating surface to gain the possibility of evaluating the aspect of the superficial fracture. The fracture surface of the coatings was observed through scanning electron microscopy in order to describe the cracking features related to the different loading conditions imposed to the coatings.