Investigation of surface hardness, thermostability, tribo-corrosion, and microstructural morphological properties of microwave-synthesized high entropy alloy FeCoNiMnCu coating claddings on steel

Deposition of high entropy alloy FeCoNiMnCu on SS-304 was carried out by microwave energy for application in "solid oxide fuel-cell (SOFC) interconnects". The ball-milling has been performed by taking "Fe, Co, Ni, Mn, and Cu" in equal 20 wt. % of before deposited on SS-304 substrate. The deposited steel with 20% Fe 20% Co 20% Ni 20% Mn 20% Cu high entropy alloy (HEA) was exposed to thermal-exposure in the air for up to 10 weeks at 800 °C. The uniform cladding distribution of 20% Fe 20% Co 20% Ni 20% Mn 20% Cu HEA particles can be apparently observed on SS-304 substrate by utilizing Scanning Electron Microscope (SEM), and Optical microscopy analysis. Homogeneity in the interfacial layer was evident by employing Scanning Electron Microscope (SEM) characterization. Results have indicated that after the thermal exposure of deposited steel with 20% Fe 20% Co 20% Ni 20% Mn 20% Cu in the air for up to ten weeks at 800 °C, a "protective Cr2O3 layer", and "high-entropy spinel coating" of (Fe, Co, Ni, Mn, Cu)3O4 have been formed. During microwave cladding, the emergence of harder-phases has contributed to the raised hardness. The wear behavior after coating of 20% Fe 20% Co 20% Ni 20% Mn 20% Cu HEA on SS-304 substrate has significantly enhanced due to the strengthened wear resistance and hardness of the coatings. Findings have exhibited that the formation of (Fe, Co, Ni, Mn, Cu)3O4 phase is a potential coating material for "SOFC interconnects" applications. Moreover, the cladding of SS304 with a composition of 20% Fe, 20% Co, 20% Ni, 20% Mn, and 20% Cu has demonstrated remarkable stability under thermal expansion studies. As the findings have revealed that the composite cladding has efficiently withstand significant variations in volume when subjected to elevated temperatures for a prolonged period of time, thus, exhibiting its superior thermal stability for SOFC-interconnect applications. Furthermore, the SEM images of the cladding surface, surface hardness, and tribocorrosion behavior of the coated material have been observed to identify the 20% Fe 20% Co 20% Ni 20% Mn 20% Cu HEA coating effect on SS-304 steel-substrate.

A review on wear, corrosion, and wear-corrosion synergy of high entropy alloys

Wear (erosion/abrasion) and corrosion act in synergy in several industrial installations where corrosive fluids circulate together with a solid phase causing mutual damage. High entropy alloys (HEAs) are promising materials to be used in that type of environments because of their outstanding chemical, electrochemical and mechanical properties. While several review articles are currently available on corrosion, mechanical properties, development of HEAs, microstructure, and HEA coatings, there is an undeniable lack of a comprehensive and critical review focusing on the tribological behaviour and tribocorrosion of bulk HEAs. This work aims to collect, summarise, and critically review the major accomplishments and progresses of HEAs over the last 20 years dealing with wear, corrosion, and wear-corrosion resistance. It highlights the most significant aspects that can influence the performance of HEAs including the change of the base alloying elements, the influence of the temperature, heat treatment, and wear test parameters (load, velocity, duration, distance). Furthermore, operating mechanisms, together with the relationship between microstructure and wear resistance, and between microstructure and corrosion resistance will be described. Finally, the articles that have been reported in the literature dealing with tribocorrosion of HEAs will be reviewed. The results of this study are expected to guide potential researchers and provide them with the sum of current trends in HEAs in terms of corrosion resistance, wear resistance and the synergy of both, in the hope of helping them to make the right decision to design and develop new HEAs or improve the research on the existing ones.

Electrochemical and hot corrosion behaviour of steel reinforced with AlSiBeTiV high entropy alloy using friction stir processing

A lightweight AlSiBeTiV high entropy alloy (HEA) powder is synthesized by the ball milling process and is reinforced on SS410 through friction stir processing (FSP). Subsequently, the annealing process is conducted on the processed samples at 450, 600, and 750°C for 120 mins. The grains are refined at 600°C by 23.3% than the processed HEA sample. A higher microhardness of 672 HV is attained on the processed HEA sample annealed at 600°C due to the synergistic effect of FSP and annealing through refined grains. The electrochemical corrosion under a 3.5 wt.% NaCl environment, and the hot corrosion under the salt mixture environments of 75% Na2SO4 +25% NaCl, and 60% Na2SO4 +20% NaCl + 20% V2O5 at 800°C for 50 h are investigated on the processed samples. The microstructure, induced corrosion products, and elemental distribution of the corroded surface of the annealed processed HEA sample are evaluated by morphological analysis. The induced oxidation effect enhances the Cr2O3 and TiO2 films on the corroded surfaces leading to higher corrosion resistance. A high corrosion resistance appears on the annealed processed HEA sample through the formation of a stable passive layer, hindering the pitting corrosion mechanism, grain refinement, and homogeneous distribution.

Phase stability and microstructural properties of high entropy alloy reinforced aluminium matrix composites consolidated via spark plasma sintering

Spark plasma sintering (SPS) technique was employed in the consolidation of Cr20Mn20Ni20Cu20Nb10Co10 high entropy alloy (HEA) reinforced aluminium matrix composites. Phase stability and prediction expressions were used in the determination of the powder combination for the HEA. The microstructural analysis showed that an interdiffusion layer was formed between the aluminium matrix and the HEA particles in the sintered composites. Further investigation of the composites by X-ray diffraction (XRD) showed that in addition to the Al matrix phase present, other new phases (BCC, FCC and other intermetallics) were formed as a result of the reaction between the Al matrix and the atoms precipitated from the added HEA during sintering. The density of the HEA-reinforced Al matrix composites decreases with an increase in the wt.% of HEA from 98.6 % for pure aluminium to 98.1 % for the reinforced alloy with 10 % HEA, while the microhardness increases with an increase in the wt.% of the HEA from 35 HV for pure aluminium to 96.0 HV for the alloy reinforced with 10 % HEA.

Phase prediction, microstructure, and mechanical properties of spark plasma sintered Ni-Al-Ti-Mn-Co-Fe-Cr high entropy alloys

The effect of mechanical alloying on the development of Ni-Al-Ti-Mn-Co-Fe-Cr high entropy alloys (HEAs) utilizing the spark plasma sintering (SPS) method is the main goal of this study. A bulk sample was fabricated using SPS after the alloys were mixed for 12 h. Thermodynamic simulation, X-ray diffraction, scanning electron microscopy, nanoindentation, and microhardness were used to investigate the microstructure and mechanical properties of the as-mixed powders. The master alloy was made of NiAl and was subsequently alloyed with Ti, Mn, Co, Fe, and Cr at different compositions to develop HEAs at a sintering temperature of 850 °C, a heating rate of 100 °C/min, a pressure of 50 MPa, and a dwelling time of 5 min. A uniform dispersion of the alloying material can be seen in the microstructure of the sintered HEAs with different weight elements. The grain size analysis shows that the Ni25Al25Ti8Mn8Co15Fe14Cr5 alloy exhibited a refined structure with a grain size of 2.36 ± 0.27 µm compared to a coarser grain size of 8.26 ± 0.43 μm attained by the NiAl master alloy. Similarly, the HEAs with the highest alloying content had a greater microstrain value of 0.0449 ± 0.0036, whereas the unalloyed NiAl had 0.00187 ± 0.0005. Maximum microhardness of 139 ± 0.8 HV, nanohardness of 18.8 ± 0.36 GPa, elastic modulus of 207.5 ± 1.65 GPa, elastic recovery (We/Wt) of 0.556 ± 0.035, elastic strain to failure (H/Er) of 0.09.06 ± 0.0027, yield pressure (H3/[Formula: see text]) of 0.154 ± 0.0055 GPa, and the least plasticity index (Wp/Wt) of 0.444 ± 0.039 were attained by Ni25Al25Ti8Mn8Co15Fe14Cr5. A steady movement to the left may be seen in the load-displacement curve. Increased resistance to indentation by the developed HEAs was made possible by the increase in alloying metals, which ultimately led to higher nanohardness and elastic modulus.

Effects of molybdenum on hot deformation behavior and microstructural evolution of Fe40Mn40Co10Cr10C0.5 high entropy alloys

The remarkable properties of high-entropy alloys (HEAs) have resulted in their increased research interest and prompted the use of various strategies to enhance their mechanical properties. In this study, the effects of Mo on the hot compressive deformation behavior of carbon-containing FeMn₄₀Co₁₀Cr₁₀ HEAs in the temperature range of 800-1000°C and strain rate of 0.001-0.1 s^-1 was investigated. The microstructural evolutilon and phase structure were characterized by X-ray diffraction and electron backscattered diffraction. The effects of strain, strain rate, and deformation temperature on the thermally activated deformation restoration process of the Fe_39.5Mn₄₀Co₁₀Cr₁₀C_0.5 and Fe_38.3Mn₄₀Co₁₀Cr₁₀C_0.5Mo_1.7 HEAs during hot compression were represented by the Zener-Hollomon parameter. Dynamic recrystallization was initiated at 800°C with the strain rate of 0.001-0.1 s^-1. The precipitation of the M₂₃C₆ carbide along the grain boundaries and within the matrix exerted a strong pinning effect on the grain/subgrain boundaries and promoted dynamic recrystallization through the particle-stimulated nucleation of recrystallization. Moreover, the addition of Mo to the Fe_39.5Mn₄₀Co₁₀Cr₁₀C_0.5 HEA changed the dynamic recrystallization mechanism by reducing the stacking fault energy and enhancing the reverse f c c ↔ h c p phase transformation. The heterogeneous microstructure composed of ultrafine, fine, and larger grains in the Fe_38.3Mn₄₀Co₁₀Cr₁₀C_0.5Mo_1.7 HEA could be obtained by the nucleation of new recrystallized grains at large deformed grain boundaries adjacent to the first necklace structures and shear bands.

Synthesis and effect of CoCuFeNi high entropy alloy nanoparticles on seed germination, plant growth, and microorganisms inactivation activity

Implementation of nanotechnology in agriculture is of interest primarily to improve the growth and productivity of crops, and to minimize the use of traditional expensive chemical fertilizers. This work presents a simple energy-conservative approach for the synthesis of CoCuFeNi high entropy alloy nanoparticles (HEA-NPs) capable of forming a stable suspension with a concentration of 0.3 g/L. The size, composition, and morphology of the nanoparticles were analyzed by XRD, SEM, TEM, and EDS. Obtained HEA-NPs were characterized by fine crystallinity with an average size of 25 nm. The investigated suspensions of HEA-NPs were tested for seeds germination and plants growth. The use of suspension of CoCuFeNi HEA-NPs for plant irrigating together with ordinary water showed positive results in plant biostimulation, which resulted in the plant height up to 12% for watercress and up to 50% for oil radish. CoCuFeNi HEA-NPs showed nice inactivation activity for Pseudomonas aeruginosa that was comparable for the use of Tetracycline.

A machine learning framework for discovering high entropy alloys phase formation drivers

In the past years, high entropy alloys (HEAs) witnessed great interest because of their superior properties. Phase prediction using machine learning (ML) methods was one of the main research themes in HEAs in the past three years. Although various ML-based phase prediction works exhibited high accuracy, only a few studied the variables that drive the phase formation in HEAs. Those (the previously mentioned work) did that by incorporating domain knowledge in the feature engineering part of the ML framework. In this work, we tackle this problem from a different direction by predicting the phase of HEAs, based only on the concentration of the alloy constituent elements. Then, pruned tree models and linear correlation are used to develop simple primitive prediction rules that are used with self-organizing maps (SOMs) and constructed Euclidean spaces to formulate the problem of discovering the phase formation drivers as an optimization problem. In addition, genetic algorithm (GA) optimization results reveal that the phase formation is affected by the electron affinity, molar volume, and resistivity of the constituent elements. Moreover, one of the primitive prediction rules reveals that the FCC phase formation in the AlCoCrFeNiTiCu family of high entropy alloys can be predicted with 87% accuracy by only knowing the concentration of Al and Cu.

Tensile creep behavior and mechanism of CoCrFeMnNi high entropy alloy

As a potential novel superalloy, the study on the creep of high entropy alloys is of great significance. Equiatomic ratio CoCrFeMnNi with a mass of 6.7 kg was fabricated by vacuum induction levitation melting. Dendrite structure is obtained for as-cast alloy while a homogeneous equiaxed grain structure can be formed after annealing at 1273 K for 6 h. The tensile creep behavior of as-annealed alloy at 773-973 K and 50-340 MPa is systematically studied. Apparent dynamic recovery and recrystallization occur for creep at 973 K while high dislocation density can be observed for creep at 923 K and lower temperatures. Results of EDS analyses on fractured surface, stress exponent and activation energy for steady state creep rate suggest that the creep mechanism should be the dislocation viscous glide dragged by solute Mn at low stresses and low temperatures and be the dislocation climb associated with Mn diffusion at high stresses and high temperatures.

Cepstral scanning transmission electron microscopy imaging of severe lattice distortions

The development of four-dimensional (4D) scanning transmission electron microscopy (STEM) using fast detectors has opened-up new avenues for addressing some of longstanding challenges in electron imaging. One of these challenges is how to image severely distorted crystal lattices, such as at a dislocation core. Here we develop a new 4D-STEM technique, called Cepstral STEM, for imaging disordered crystals using electron diffuse scattering. In contrast to analysis based on Bragg diffraction, which measures the average and periodic scattering potential, electron diffuse scattering can detect fluctuations caused by crystal disorder. Local fluctuations of diffuse scattering are captured by scanning electron nanodiffraction (SEND) using a coherent probe. The harmonic signals in electron diffuse scattering are detected through Cepstral analysis and used for imaging. By integrating Cepstral analysis with 4D-STEM, we demonstrate that information about the distortive part of electron scattering potential can be separated and imaged at nm spatial resolution. We apply the technique to the analysis of a dislocation core in SiGe and lattice distortions in a high entropy alloy.

Tailoring biocompatible Ti-Zr-Nb-Hf-Si metallic glasses based on high-entropy alloys design approach

Present work unveils novel magnetic resonance imaging (MRI) compatible glassy Ti-Zr-Nb-Hf-Si alloys designed based on a high entropy alloys approach, by exploring the central region of multi-component alloy phase space. Phase analysis has revealed the amorphous structure of developed alloys, with a higher thermal stability than the conventional metallic glasses. The alloys exhibit excellent corrosion properties in simulated body fluid. Most importantly, the weak paramagnetic nature (ultralow magnetic susceptibility) and superior radiopacity (high X-ray attenuation coefficients) offer compatibility with medical diagnostic imaging systems thereby opening unexplored realms for biomedical applications.

High resolution atomic scale characterization of dislocations in high entropy alloys: Critical assessment of template matching and geometric phase analysis

The paper assesses the applicability of advanced atomic resolution displacement measurement techniques to characterize dislocation character in metallic materials using simulated images derived from anisotropic elasticity and actual measurements in high entropy alloys. We draw attention to two techniques: the real space method of template matching (TeMA) and the reciprocal space method of geometric phase analysis (GPA) and provide a critical assessment. These techniques have limitations for direct evaluation of full dislocations Burgers vector or when local displacements are exceeding 50% lattice spacing. This is clearly illustrated with simulated arctangent displacement profiles reminiscent of dislocation cores. An approach for circumventing this limitation is suggested in the form of a nearest neighbor correction. Additionally, a methodology for determination of the Burgers vector is introduced on the basis of a vectorial rendering of the displacement field upon consideration of two zone axis measurements and applied to TeMA and GPA. The experimental results conform to the Burgers vector of a full lattice dislocation in the FCC crystal structure of the High-Entropy Alloy (HEA). The comparison of simulated and experimental images proves the efficacy of the HR-TEM (High Resolution Transmission Electron Microscopy) displacement mapping techniques while pointing to the need for caution in case of large displacements.

Short-range ordering induced serrated flow in a carbon contained FeCoCrNiMn high entropy alloy

Phase stability of high entropy alloys depends significantly on the compositional constituents. Here we report the joint effects of interstitial carbon and compositional inhomogeneity on the mechanical response, particularly the serrated flow, of a carbon doped FeCoCrMnNi high entropy alloy. Detailed microstructural characterizations show that compositional inhomogeneity, including heterogeneous short-range ordering structure, is formed in carbon doped FeCoCrNiMn HEA. The serrated flow on the stress-strain curves of carbon doped alloy at room temperature is attributed to the dynamic strain aging, which is presented based on the complex interactions between carbon, stacking faults and short-range ordering at the atomic scale.

Exceptionally high cavitation erosion and corrosion resistance of a high entropy alloy

Cavitation erosion and corrosion of structural materials are serious concerns for marine and offshore industries. Durability and performance of marine components are severely impaired due to degradation from erosion and corrosion. Utilization of advanced structural materials can play a vital role in limiting such degradation. High entropy alloys (HEAs) are a relatively new class of advanced structural materials with exceptional properties. In the present work, we report on the cavitation erosion behavior of Al_0.1CoCrFeNi HEA in two different media: distilled water with and without 3.5wt% NaCl. For comparison, conventionally used stainless steel SS316L was also evaluated in identical test conditions. Despite lower hardness and yield strength, the HEA showed significantly longer incubation period and lower erosion-corrosion rate (nearly 1/4th) compared to SS316L steel. Enhanced erosion resistance of HEA was attributed to its high work-hardening behavior and stable passivation film on the surface. The Al_0.1CoCrFeNi HEA showed lower corrosion current density, high pitting resistance and protection potential compared to SS316L steel. Further, HEA showed no evidence of intergranular corrosion likely due to the absence of secondary precipitates. Although, the degradation mechanisms (formation of pits and fatigue cracks) were similar for both the materials, the damage severity was found to be much higher for SS316L steel compared to HEA.