Gradient Layer Research Articles

Study of the effect of magnetic field characteristics on Rayleigh-Taylor instability with density gradient layers

Inertial confinement fusion (ICF) is a possible path of fusion technology for fusion ignition, but during the implosion of a magnetized plasma target by compression, the magnetic Rayleigh-Taylor (R-T) instability similar to that at the interface of the denser and less dense phases can arise when the plasma is subjected to gravitational and magnetic forces, which in turn affect the confinement characteristic and the process of fusion burn. In this study, the R-T instability of two phases in the presence/ absence of a magnetic field in a two-dimensional rectangular duct is simulated based on the MHD model adopted in ANSYS FLUENT. The simulation results show that the R-T instability is substantially weakened for the case with an Atwood number of 0.29 where a constant (DC) magnetic field is imposed in the opposite direction to the gravitational acceleration, meanwhile, a strong countercurrent flow, which occurs near the side walls, enhances the heat and mass transport process, which is related to the M-shape velocity profile formed in the flow channel. Besides, when a DC magnetic field perpendicular to the direction of the gravitational acceleration is introduced, the R-T instability vanishes from the initial moment to the end. When a sinusoidal wave form of varying (AC) magnetic field is introduced, the R-T instability is substantially facilitated. The evolutions of the interface and pressure field distribution are significantly correlated with the change in intensity and direction of the AC magnetic field. After about one cycle of the magnetic field's variation, the density gradient layers in the vertical direction are entirely converted to a density stratification in the horizontal direction with the denser phase occupying the region near the sidewalls of the duct, and ever since then, the R-T instability disappears completely. These findings can provide supports for the design of nuclear fusion devices and magnetic fields.

Precursor-oriented ultrathin Zr-based gradient coating on Ni-riched cathodes

We present a simple and low-cost interfacial precipitation-conversion reaction strategy, which employs the precursors as orientators to coat ultrathin and surface-gradient layers for reserving the structural integrality and stability of particularize materials. Using the typical high-nickel layered cathode (LiNi0.8Co0.15Al0.05O2, NCA) as a prototype, we successively processed NCA carbonate oxalate precursors with (NH4)2HPO4 and ZrOCl2 solutions to chemically induce Zr species on the NCA surfaces via strong M-PO4-Zr interactions (M = Ni, Co). An ultrathin Zr-contained gradient layer is in-situ self-assembled spontaneously and conformably (NCA@ZP) after calcination. The as-designed NCA@ZP cathode delivers a high capacity of 219.7 mA h·g−1, 23% higher than NCA (179.0 mA h·g−1) at 0.1 C, and exhibits superior rate capability (128.2 mA h·g−1 capacity at 16 C) and cycling stability. Experimental characterization together with calculation further reveal that the residential Zr element at Li+ sites strengthen the adjacent M-O bonds, inhibiting the oxygen evolution and dissolution of transition metal, buffering the internal strains, stabilizing the cathode-electrolyte interface, improving the electrical conductivity and consequently benefiting the cyclability and rate capability. Such a simple precursor-oriented strategy can be easily scaled-up and extended to various application scenarios who encounter unwanted side-reactions or structural degradation during chemical reactions.

Composition controls soft hydrogel surface layer dimensions and contact mechanics.

Hydrogels are soft hydrated polymer networks that are widely used in research and industry due to their favorable properties and similarity to biological tissues. However, it has long been difficult to create a hydrogel emulating the heterogeneous structure of special tissues, such as cartilage. One potential avenue to develop a structural variation in a hydrogel is the "mold effect," which has only recently been discovered to be caused by absorbed oxygen within the mold surface interfering with the polymerization. This induces a dilute gradient-density surface layer with altered properties. However, the precise structure of the gradient-surface layer and its contact response have not yet been characterized. Such knowledge would prove useful for designs of composite hydrogels with altered surface characteristics. To fully characterize the hydrogel gradient-surface layer, we created five hydrogel compositions of varying monomer and cross-linker content to encompass variations in the layer. Then, we used particle exclusion microscopy during indentation and creep experiments to probe the contact response of the gradient layer of each composition. These experiments showed that the dilute structure of the gradient layer follows evolving contact behavior allowing poroelastic squeeze-out at miniscule pressures. Stiffer compositions had thinner gradient layers. This knowledge can potentially be used to create hydrogels with a stiff load-bearing bulk with altered surface characteristics tailored for specific tribological applications.

Resistance brazing of C/C composites-metallized SnAgCu-Ti powder to T2 copper using AgCuTi filler metal

Carbon/carbon (C/C) composites and T2 copper (Cu) alloy were successfully welded by the following two-step process: the pre-metallization on C/C composites was successfully prepared by the vacuum brazing welding using SnAgCu-xTi(x = 1, 2, 3, 4, and 5 wt%) metal powder and the subsequent reliable C/C composites-Cu joints were obtained by resistance brazing welding with AgCuTi filler metal as the interlayer in this paper. The typical interface morphology of the metallization layer on the surface of C/C composites, microstructure, mechanical properties, and fracture mechanism of resistance brazing welded joints were investigated by the relevant analysis method. The smooth metallization layer was generated on the surface of the C/C composites in the pre-metallization process successfully. The formed excellent bonding between the metallization layer and C/C composites in this stage was prepared for the subsequent welding process. Meanwhile, a strong interfacial bond was obtained due to the formation of the TiC reaction layer in the subsequent resistance brazing welding process. Molten solder infiltrated the pores of the C/C composites and formed a ‘pinning structure’. The residual thermal stress and mismatch of CTE could be relieved by the gradient layer and the shear strength could reach 19.68 MPa.

In situ 3D printing of poly-ether-ether-ketone / poly-ether-imide hierarchical cellular foams containing electromagnetic absorbent

For the expanding application of light-weight integral structures meeting both structural and physical requirements, the development of advanced materials with high performances in multiple functions and their automatically manufacturing processes with mass production potential at low cost has received sustained attention from both academia and industry. Therefore, an in situ 3D printing technology of poly-ether-ether-ketone (PEEK)/ poly-ether-imide (PEI) hierarchical cellular foam containing electromagnetic absorbent was proposed in this paper. Fillers with electromagnetic functions, nano-carbon and Fe 3 O 4 , were introduced into the blend of two high-performance thermoplastics, semicrystalline PEEK and amorphous PEI, and a lightweight nanocomposite foam with functionalized hierarchical cellular structure in micrometer scale was manufactured by combining in situ foaming process into 3D printing. The in situ foaming mechanism of the materials was carefully studied and optimal process parameters were obtained. When the desorption time of materials is 48 h, the 3D printed foams present the smallest cell size and the highest cell density. The foaming behavior of this special material is different from that of batch foaming. Mechanical tests show that the flexural modulus increases with decreasing cell size and increasing cell density. In X-band (8.2–12.4 GHz), the hierarchical cellular structure with gradient layers performs low reflectivity and absorption-dominant EMI shielding properties. The lightweight nanocomposite foam manufactured by the in situ 3D printing technology have great potential for applications such as functional-structural integrated skins in aerospace, protection of high-power instruments and 5 G communication products.

One step co-sintering synthesis of gradient ceramic microfiltration membrane with mullite/alumina whisker bi-layer for high permeability oil-in-water emulsion treatment

Developing a permeation property and reducing the cost for ceramic microfiltration membrane are significant challenges and target. In this study, a gradient structure ceramic microfiltration membrane with mullite/alumina whisker bi-layer was successfully prepared using the dry-pressing method and one-step co-sintering process. In addition, the co-sintering conditions of substrate and whisker layer, the pore size regulations of whisker layer and emulsified oily wastewater filtration performance of the ceramic microfiltration membranes were systematically investigated. The gradient structure ceramic microfiltration membranes with high bonding strength and flexural strength were obtained under a co-sintering temperature of 1300 °C, and the average pore size of ceramic membrane was approximated in 120 nm, through the coordinated adjustment of the gradient layer by mullite whisker and alumina whisker. The filter performance results showed that with the synergistic effect of high porosity and low tortuosity of the whisker stacking membrane structure, the obtained ceramic membrane exhibited high permeability performance and oil rejection efficiency. The separation fluxes of oil-in-water emulsion with 500 and 1000 mg/L were 901 and 547 L/(m2·h·bar), respectively, and the oil rejection efficiency was higher than 99%. Even after 10 filtration cycles, the separation flux was still steady at 415 L/(m2·h·bar) for the separation process of oil-in-water emulsion with 1000 mg/L. In conclusion, the excellent pore structure of ceramic membrane with whisker layer endowed the separation flux for the oil-in-water emulsion, and the one-step co-sintering indicated a promising practical application for reducing the cost of ceramic microfiltration membranes.

Study on microstructure and abrasive behaviors of inconel 718-WC composite coating fabricated by laser directed energy deposition

Additive manufacturing enables the development of high-performance materials by in-situ alloying of multiple components. In this study, Inconel 718-based composite, reinforced with tungsten carbide (WC), was synthesized on a 316L stainless steel substrate using laser directed energy deposition (DED). The microstructural evolution, distribution density of WC particles, and strengthening mechanisms of the DED-processed metal matrix composite (MMC) with different WC particle sizes and ratios are systematically investigated. It illustrated that increasing laser power enables the microstructure transforming from equiaxed to dendritic, which is attributed to the different cooling rates and temperature gradients. In addition, the morphology of the 60% WC ratio of the particle composite shows macrocracks. The incorporation of different sized WC affects retained WC distribution density and tailors a gradient layer around the edge of the WC particle. The in-situ WC-W2C phases precipitated in the deposited layer and the evenly distributed high level of ex-situ retained WC particles induce solid solution strengthening and dispersion strengthening, respectively. As a result, the optimal size of the 90 μm WC/Inconel 718 shows the highest wear resistance. The underlying strengthening mechanisms are elucidated. Consequently, the wear mechanism of Inconel 718-based composite reveals the typical abrasive wear characteristics in the presence of WC particles.

Microstructure and mechanical behavior of functionally graded cemented carbides with CoNiFeCr multi-principal-element alloy binder

In this work, functionally graded cemented carbides (FGCCs) with CoNiFeCr multi-principal-element alloy (MPEA) binder were prepared by pre-sintering and carburizing. The microstructure and mechanical behavior of WC-CoNiFeCr FGCCs with different carbon contents obtained at different carburization temperatures were studied. The results showed that a higher carbon content simultaneously accelerated the diffusion rate of carbon and increased the diffusion channel of carbon. The FGCC with a carbon content of 4.55% obtained at a carburizing temperature of 1450 °C exhibited the thickest gradient layer and the highest extreme hardness difference, TRS, and fracture toughness. Moreover, as the thickness of the gradient layer increased, the fatigue sensitivity of FGCCs enhanced, approaching the characteristics of metallic materials.

Material properties of gradient copper‐nickel alloy fabricated by wire arc additive manufacturing based on bypass-current PAW

In this paper, the bypass-current plasma arc welding (BC-PAW) based on PAW was employed to fabricate copper-nickel (Cu-Ni) gradient thin-walled structures. The effect of forming accuracy and compositional homogeneity of the bypass current Cu-Ni structure was first verified by controlled experiments. The effect of Ni content on the microstructure and mechanical properties of Cu-Ni gradient structures fabricated using bypass current was then investigated, with a focus on grain orientation and texture analysis of the three intermediate Cu-Ni mixed gradient layers. The results showed that the use of bypass current in the additive manufacturing of Cu-Ni gradient structures can improve the forming accuracy and effectively eliminate lateral composition deviations within the gradient layers. In the Cu-Ni mixed gradient layers, the average grain size of the gradient layers decreased with increasing nickel content, and unusually large secondary grains appeared in different gradient layers. Due to the different Ni content, different degrees of amplitude modulation decomposition occurred in different gradient layers, resulting in changes of grain orientation and texture composition. Under the combined effects of solid solution strengthening, fine grain strengthening and amplitude modulation decomposition, the microhardness and tensile strength increased with increasing nickel content and then decreased, reaching a maximum near the side of the gradient composition biased toward nickel. The fracture analysis showed a transition from ductility to quasi-fracture.

Microstructure evolution and strength-toughness matching mechanism of Fe-Cr-Ni gradient alloy steel prepared by direct laser deposition

A novel 70Cr8Ni2Y alloy steel powder was designed and prepared to meet the requirement for composition design and preparation of gradient alloys with strength-toughness matching the preparation of nuclear power camshafts by direct laser deposition (DLD). A three-layer gradient structure alloy sample with strength-toughness matching was successfully prepared by DLD using 70Cr8Ni2Y, 50Cr6Ni2Y and 12CrNi2Y alloy steel powder. The microstructure evolution and strength-toughness matching mechanism of the gradient sample were studied. The interfaces between the gradient layers were metallurgical bonding and had no defects such as cracks and pores. With the change of the alloy composition of the three gradient layers, the main microstructure of the sample changed from granular bainite to lath bainite, and to martensite in turn. The mechanism of strength-toughness matching was that the changes of the three alloy components made the strength of microstructure increase, and a metallurgical bond formed at the interfaces of the gradient layers. The gradient sample demonstrated strength-toughness matching of high-strength surface and good toughness core through adjusting of the gradient layers and change of microstructure. The high-strength 70Cr8Ni2Y surface layer ensured the high hardness and wear resistance of the gradient sample, and the 50Cr6Ni2Y gradient layer acted as an intermediate layer to support the surface and protect the bottom layer. The 12CrNi2Y gradient layer with good toughness played a role in delaying fracture and hindering crack propagation. The microhardness of the gradient sample showed a gradient distribution of 739-534-321 HV. The average tensile strength was 1076 MPa, the elongation was 1.6%, and the specific wear rate (SWR) of the sample surface was 9.5 × 10−5 mm3/(N·m). This paper can provide a useful reference for the preparation of nuclear power camshaft parts with gradient properties of good toughness of the core and high hardness and wear resistance of the surface by DLD.

Microstructure and formation mechanism of Al2O3/Zn5Al/2024Al joint by ultrasonic assisted soldering process

Zn5Al filler metal was used to join 2024Al and Al2O3 ceramic with the ultrasonic assisted soldering process in the atmospheric environment. Al2O3 ceramics were dipped by molten Zn5Al alloy (melting temperature: 382 °C) with the time of ultrasonic action for 5– 600 s, respectively. During the ultrasonic assisted soldering process, the ultrasonic was applied for 1 s, the Al2O3 ceramic was subjected to a pressure of 0.2 MPa. To reduce the residual stress, the soldered joint was cooled in the furnace. 2024Al had better metallurgical fusion with Zn5Al filler metal. The grain boundary on the 2024Al was partially dissolved by Zn5Al filler metal. The fan-shaped α-Al eutectic phases were distributed on the gradient layer. With the increase of the ultrasonic dipping time, more fine β-ZnAl phases were accumulated on the Al2O3 ceramic surface. The Al2O3/Zn5Al/2024Al joint with ultrasonic dipping time of 600 s had the highest shear strength (39.53 MPa). The soldered joint fractured mainly in cohesive failure mode, and the joint broke from the Zn5Al filler metal.

Impact of Land Cover Change on Mountain Circulation over the Hainan Island, China

Focusing on the complex underlying surface area in central–southern Hainan Island, this study uses the Advanced Research Weather Research and Forecasting Model (Version 4.0) to simulate a typical mountain circulation case without obvious weather system forcing, and tries to reveal the impacts of land cover changes on the mountain circulation. One control experiment (CNTL) and three sensitivity experiments, in which the current land cover is taken as areas of uniform evergreen broadleaf forest (FOREST), grassland (GRASS), and bare soil (DESERT) coverage, are conducted. The results show that the near-surface wind speed increases with decreasing surface roughness, and DESERT shows the most obvious change as compared with the CNTL. In the vertical direction, FOREST shows the strongest valley breeze circulation, with the largest horizontal and vertical extents of circulation, as well as the highest vertical extent of the updraft. DESERT shows the weakest valley breeze circulation with the longest duration. GRASS shows the slightest change from the CNTL. The possible impact mechanism is that the land cover changes could affect the surface energy partitioning, leading to a variation in the temperature distribution (i.e., the horizontal potential temperature gradient and boundary layer stability), in turn affecting the structure and evolution characteristics of the mountain circulation.

Synthesis and Characterization of High‐Entropy CrMoNbTaVW Thin Films Using High‐Throughput Methods

High‐entropy alloys (HEAs) or complex concentrated alloys (CCAs) offer a huge research area for new material compositions and potential applications. Since the combination of several elements sometimes leads to unexpected and unpredictable material properties. In addition to the element combinations, the optimization of the element proportions in CCAs and HEAs is also a decisive factor in tailoring desired material properties. However, it is almost impossible to achieve the composition and characterization of CCAs and HEAs with a sufficient number of compositions by conventional experiments. Therefore, an optimized high‐throughput magnetron sputtering synthesis to fabricate a new HEA gradient layer of six elements is presented. With this approach, the compositional space of the HEA system CrMoNbTaVW can be studied in different subsections to determine the influence of the individual elements and their combinations on the structure, morphology, and physical properties (hardness and resistivity). It is found that the Cr‐, Ta‐, and W‐rich phases, which have a grain size of 10–11 nm, exhibit the hardest mechanical properties, whereas V‐, Ta‐, and Cr‐rich compounds exhibit the highest electrical resistivity. The combination of high‐throughput synthesis, automated analysis tools, and automated data interpretation enables rapid and time‐efficient characterization of the novel CrMoNbTaVW gradient film.

Crashworthiness of lantern-like lattice structures with a bidirectional gradient distribution

Oblique impact loading conditions strongly influence the crashworthiness of energy-absorbing structures. In the present work, inspired by the distribution characteristics of spider webs, a bidirectional gradient configuration of cell wall thickness was introduced to enhance the crashworthiness of lattice structures based on the functional similarity of longitudinal gradient distribution and lateral gradient distribution. A comparative study of different gradient configurations was carried out using the finite element (FE) simulations. It was found that the longitudinal gradient distribution was beneficial to improve the comprehensive energy absorption capacity of the lattice structure, especially under small-angle impact conditions. With the increase of impact angle, the effect of the lateral gradient distribution on the stability of energy absorption became more prominent. In comparison to the uniform structure and the single gradient structure, the lattice structure with the positive longitudinal gradient and the negative lateral gradient distribution exhibited great potential in enhancing the energy absorption capacity and reducing the peak crushing force. A detailed parametric study was executed to explore the effects of the gradient layer number and the gradient thickness increment of the bidirectional gradient distribution on the comprehensive energy absorption capacity and energy absorption stability of the structure under multi-angle impact conditions. The findings of this research provide valuable guidelines to design bio-inspired lattice structures subjected to complex loading conditions.

Synergetic-Deformation-Induced Strengthening in Gradient Nano-Grained Metals: A 3D Discrete Dislocation Dynamics Study

Gradient nano-grained (GNG) metals have shown high synergetic strength and good ductility due to their unique gradient microstructure. In this study, the mechanical behavior of gradient nano-grained metals was investigated by three-dimensional discrete dislocation dynamics. The simulation results show a trend that the successive yielding and gradual “transmission” of dislocations along the gradient direction result in a gradient distribution of stress and plastic strain. The distribution of geometrically necessary dislocations is more inhomogeneous in the gradient nano-grained (GNG) sample compared with those homogenous counterparts. The non-uniform deformation response of component layers induces the synergetic-deformation-induced (SDI) strengthening in the GNG sample. The back stress originates from geometrically necessary dislocations that pile up near the interface of gradient layers and leads to a significant hardening while there is a slight softening in different gradient layers in the GNG sample. This study provides a deeper insight into the SDI strengthening in gradient structure from the submicron scale.

Bending fatigue life enhancement of NiTi alloy by pre-strain warm surface mechanical attrition treatment

Many structures like medical stents made of superelastic NiTi shape memory alloy (SMA) are subjected to cyclic bending loads and show a limited fatigue life due to crack nucleation and growth in the surface layers under local tensile stress. Here, we enhance the bending fatigue life of NiTi plates by pre-strain warm surface mechanical attrition treatment (pw-SMAT) where the austenite phase is directly subjected to severe plastic deformation and grain refinement without inducing phase transformation. Amorphous and grain size gradient (5–100 nm) microstructures, as well as a maximum compressive residual stress of 1093 MPa are produced in the surface layer of the NiTi plates via the pw-SMAT. The compressive residual stress notably reduces the surface tensile stress from bending. The grain size gradient layers with improved hardness and reduced hysteresis have high fatigue crack nucleation resistance, while the middle large-grained layers of the plates have high fatigue crack growth resistance. The combined effects of the gradient nanostructure and the compressive residual stress substantially increase the bending fatigue life of the NiTi plates from an original 103 cycles to over 1.3 × 104 cycles. The results open up a new route to improve the bending fatigue life of NiTi plates by heterogenous nanostructures.

Constructing interfacial gradient layers and enhancing lithium salt dissolution kinetics for high-rate solid-state batteries

The stability of the interfacial layers depends mainly on the composition and distribution of the decomposition products from solid-state electrolytes (SSEs) in lithium metal batteries. Therefore, the design of SSEs becomes an attractive way to construct a homogeneous stable interfacial layer. Herein, pentafluorostyrene (PFS) as a block is used to generate robust interfacial layers for solid-state batteries. Meanwhile, PFS facilitates the dissociation of lithium salts to produce more free Li-ions which can enhance the ionic conductivity from the results of 7Li solid-state NMR spectra, density functional theory, and molecular dynamics calculations. Subsequently, XPS depth etching and TOF-SIMS characterizations together show that the gradient interfacial layer is composed of a rich C-F bond surface layer and a rich–LiF&Li3N bottom layer, enabling rapid transport and uniform deposition of lithium ions. As a result, the Li/Li symmetric cell can achieve a stable ultra-long cycle time of more than 3000 h at 0.2 mA cm−2 and a critical current density of 2.4 mA cm−2. The as-prepared SSE exhibits a high ionic conductivity of 4.3 × 10−4 S cm−1 at 25 °C and remarkable cycling stability at 0 °C and − 20 °C. Moreover, the lithium metal batteries based on as-prepared SSEs deliver high-rate (2 C) capability and high-voltage (NCM811) stability at room temperatures.

Experimental study of multilayer gradient copper foam effect on pool boiling heat transfer performance and gas-liquid behavior characteristics

The rapid growth of the internet of things has induced the integration of many microelectronic devices in physical objects, yet the generated heat decreases the performance and stability of microelectronic devices. Therefore, new materials such as gradient metal foams (GMFs) have been recently designed to improve heat transfer. In this paper, an experimental visualization setup was built to investigate the effect of the GMFs gradient layers number and the arrangement order on the pool boiling heat transfer performance. Results show that increasing the number of gradient layers enhances the heat transfer when the copper foam pore density is low. By contrast, at high pore density of 50 PPI, increasing layers hardly changes heat transfer. The bubbles dynamic behavior on the metal foams surface of with different gradient structures is also different. When bubbles detach upward, the temperature of the metal foam is lower, and the temperature gradient is higher. When bubbles detach sideward, the bubble escape is much shorter, and the bubble detachment frequency and size increase. Combined with the theoretical research, the metal foam gas-liquid flow heat transfer model were constructed. The advantages and disadvantages of GMFs with different structures and the applicable scenarios are analyzed.

Efficacy of density gradient centrifugation technique (DGC) in enhancing sperm cell DNA quality for assisted reproductive technique

ObjectiveDensity gradient centrifugation (DGC) is commonly used for sperm preparation before assisted reproductive technology (ART) procedures. This technique separates superior motile spermatozoa with normal morphology from the total sperm population. However, there is still controversy as to the effects of this sperm separation technique on sperm cell DNA integrity which is a determining element in the process of fertilization and embryonic development.The objective of this study was to determine the effects of DGC on sperm cell DNA integrity as assessed by a novel association between two cytogenetic tests.Study designsSemen samples were collected from 30 fertile donors and 40 patients being candidates for ART treatment. Each sample was divided into two parts: the first portion was subjected to selection by two layers of DGC (45% and 90%) and the second fraction was rinsed with phosphate-buffered saline solution and centrifuged without density gradient.Abnormal sperm chromatin structure as evaluated by a sperm chromatin dispersion (SCD) test and DNA denaturation as assessed by an acridine orange (AO) test were monitored in the initially washed sample and in the different layers of the density gradient centrifugation.ResultsDGC significantly improved the proportion of sperm progressive motility, total motility, and sperm morphology. Moreover, following density gradient centrifugation, the proportion of spermatozoa with denaturated DNA significantly decreased when compared with whole semen (p < 0.001). In addition, we found that spermatozoa isolated in the 90% layer possessed a significantly lower percentage of sperm chromatin decondensation when compared with those remaining in the 45% layer and unprocessed semen (p < 0.001).ConclusionsUsing double cytogenetic tests, our study shows that semen processing by density gradient centrifugation is useful in selecting sperm with higher double-strand DNA integrity and recommended to be used in sperm preparation for assisted reproduction.

Low-cycle fatigue behavior and surface treatment of a twinning-induced plasticity high-entropy alloy

The low-cycle fatigue life and cyclic deformation behavior of a metastable high-entropy alloy were investigated in this study. Additionally, the effects of the ultrasonic nanocrystal surface modification (UNSM) process on tensile properties and fatigue life were evaluated. Heat treatment following the cold rolling of Fe40Mn40Co10Cr10 alloy plates resulted in the formation of a coarse grain size of 46.7 ± 19.6 μm. Additional mechanical twins were activated during tensile testing compared to the equiatomic CoCrFeMnNi alloy, leading to increased elongation. However, mechanical twins in cyclic loads appear only at high strain amplitudes. Therefore, similar to the CoCrFeMnNi alloy, the slip of dislocations was the dominant cyclic deformation mechanism and the fatigue life of the alloys were comparable. The UNSM process formed a deformed gradient layer with a thickness of approximately 200 μm on the alloy surface. In addition to mechanical twins and low-angle grain boundaries, ultrafine grains with diameters as small as 200 ± 120 nm are detectable in this layer. Although this surface treatment successfully increased the yield strength by more than 70%, fatigue crack initiation was accelerated and fatigue crack growth resistance was degraded.