Face-centered Cubic Research Articles

A Complex Concentrated Alloy with Record-High Strength-Toughness at 77 K.

High strength and large ductility, leading to a high material toughness (area under the stress-strain curve), are desirable for alloys used in cryogenic applications. Assisted by domain-knowledge-informed machine learning, here a complex concentrated Fe35Co29Ni24Al10Ta2 alloy is designed, which uses L12 coherent nanoprecipitates in a high volume fraction (≈65 ± 3 vol.%) in a face-centered-cubic (FCC) solid solution matrix that undergoes FCC-to-body-centered-cubic (BCC) phase transformation upon tensile straining. Unlike FCC-to-BCT phase transformation involving brittle carbon-enriched martensite, the BCC martensite in this alloy does not cause brittleness at 77 K. The Fe35Co29Ni24Al10Ta2 multi-principal element alloy achieves a high yield strength ≈1.4GPa, a high work hardening rate >4GPa, an ultimate tensile strength ≈2.25GPa, and a large uniform elongation ≈45%, leading to record-high material toughness compared with previous cryogenic alloys such as 316L series stainless steels and recent high-entropy alloys. The nanoprecipitates with nanoscale spacing (≈7.5nm), apart from serving as dislocation obstacles for strengthening and dislocation sources for sustainable ductility, also undergo deformation twinning. Taken together, these mechanisms are found to be highly effective in strengthening and strain hardening upon tensile straining at liquid nitrogen temperature. These findings demonstrate how to effectively integrate strengthening mechanisms to synergize superior mechanical properties in special-purpose alloys.

New insights from DFT analysis: Mg vacancies and hydrogen doping in enhancing thermodynamic properties and hydrogen storage performance of Li2BeMgH6

To identify effective hydrogen storage materials, a novel study employing first-principles calculations based on density functional theory DFT on the lithium-based double perovskite hydride Li2BeMgH6. This material, with its innovative and significant attributes, emerges as a potential candidate for hydrogen storage, inspiring experimental researchers to pursue its synthesis for the experimental fabrication of hydrogen storage devices. Notably, it boasts a remarkable gravimetric capacity of 11.35 wt%, coupled with exceptional stability and desorption temperature, surpassing the standards set by the U.S. Department of Energy (DOE) for solid-state hydrogen storage (ΔH = −40 kJ/mol.H2 and Td = 289 K–393 K), with respective values of ΔH = −77.37 kJ/mol H2 and Td = 591 K for the cubic phase and ΔH = −84.64 kJ/mol H2, Td = 647 K for the rhombohedral structure. This comprehensive research aims to demonstrate the thermodynamic stability of this innovative material and improve its hydrogen storage properties in line with DOE requirements. The results obtained highlight the significant impact of two strategies for enhancing hydrogen storage properties in two stable phases (face-centered cubic (fcc) and rhombohedral (R3)): the creation of magnesium vacancy defects and hydrogen doping in the Mg vacancies in the studied system. The first strategy, involving the generation of 6 % defects in the Mg atoms, resulted in a notable improvement in storage properties, with a gain of 50.75 % for the cubic structure and 50.46 % for the rhombohedral structure. The second strategy, which consists of doping the vacant Mg sites with hydrogen, also demonstrated remarkable efficiency, leading to an increase of 50.05 % and 53.07 % in storage performance for the two phases, respectively.

Grain refinement and mechanical properties improvement of AlCuFeCoNi high-entropy alloy coatings fabricated by resonant ultrasonic assisted laser cladding

Laser cladding technology has gained significant popularity for the preparationof high-entropy alloy (HEA) coatings. This is primarily due to its notable benefits, such as a low dilution rate and a robust bonding capability. However, the laser cladding process’s rapid solidification effect and the high entropy impact led to the formation of defects in the coatings, such as non-uniform organization and elemental segregation. In this paper, the resonant ultrasonic vibration was used to regulate the organization and improve the microhardness and friction properties of the AlCuFeCoNi HEA coatings. The experimental findings demonstrate that ultrasonic vibration enhances both the width and depth of the coating’s molten state, while simultaneously reducing the height of the coating. Before and after the introduction of ultrasonic vibrations, the coating consists of two phases, body-centered cubic (BCC) and face-centered cubic (FCC). However, the magnitude of the FCC phase significantly increased with higher power. The internal grains of the coating were significantly refined by ultrasonic vibration, and the average grain size was refined from 68.34 μm to 35.28 μm, and the area occupied by equiaxial grains also increased with the increase of ultrasonic power, and the segregation of the FCC phase dominated by Cu elements was suppressed. When the ultrasonic power was 30 %, the microhardness of the coating was increased from 553.19 ± 5.15 HV0.2 to 600.47 ± 3.61 HV0.2. The addition of ultrasonic vibration increased the wear resistance of the coating and lowered the coefficient of friction from 0.558 to 0.409. Furthermore, the friction mechanism of the coatings before and after the addition of ultrasonic vibration did not change, and both were abrasive wear with slight oxidative wear.

Surface Structure Dependent Activation of Hydrogen over Metal Oxides during Syngas Conversion.

Despite the extensive studies on the adsorption and activation of hydrogen over metal oxides, it remains a challenge to investigate the structure-dependent activation of hydrogen and its selectivity mechanism in hydrogenation reactions. Herein we take spinel and solid solution MnGaOx with a similar bulk chemical composition and study the hydrogen activation mechanism and reactivity in syngas conversion. The results show that MnGaOx-Solid Solution (MnGaOx-SS) is a typical Mn-doped hexagonal close-packed (HCP) Ga2O3 with a Ga-rich surface. Upon exposure to hydrogen, Ga-H and O-H species are simultaneously generated. Ga-H species are highly active but unselective in CO activation, forming CHxO, and ethylene hydrogenation, forming ethane. In contrast, MnGaOx-Spinel is a face-centered-cubic (FCC) spinel phase featuring a Mn-rich surface, thus effectively suppressing the formation of Ga-H species. Interestingly, only part of the O-H species are active for CO activation while the O-H species are inert for olefin hydrogenation over MnGaOx-Spinel. Therefore, MnGaOx-Spinel exhibits a higher activity and higher light-olefin selectivity than MnGaOx-SS in combination with SAPO-18 during syngas conversion. These fundamental understandings are essential to guide the design and further optimization of metal oxide catalysts for selectivity control in hydrogenations.

Exceptional tensile ductility and strength of a BCC structure CLAM steel with lamellar grains at 77 kelvin

The low-temperature tensile brittleness of body-centered cubic (BCC) metals and alloys can seriously compromise their service applications. In this study, we prepared a BCC structured China low activation martensitic steel (CLAM) steel with lamellar grains by regulating the rolling and heat-treatment processes, successfully reversing the decreasing trend of ductility in the steel with decrease in temperature. Compared with current face-centered cubic (FCC) structural steels and high-entropy alloys, the lamellar grained CLAM steel exhibits an excellent synergy of strength and ductility at 77K, but with lower raw material costs. The superior low temperature ductility of the lamellar grained steel can be attributed to an increase in grain strength at low temperatures which promotes the propagation of layered tearing cracks; this in turn leads to a significant increase in the necking area of the steel, thereby compensating for the decrease in ductility. We conclude that our lamellar grain structures can be utilized to significantly enhance the low-temperature tensile ductility of BCC metals and alloys, thereby expanding their service range to cryogenic temperatures.

Atomistic simulation of chemical short-range order on the irradiation resistance of HfNbTaTiZr high entropy alloy

High entropy alloys (HEAs) have been considered as one of the potential structural material candidates for fourth-generation nuclear reactors and fusion reactors due to their excellent irradiation resistance. Current studies have shown that the chemical short-range order (CSRO) usually exists in HEAs, which has a significant effect on the mechanical properties and irradiation resistance of HEAs. Refractory high entropy alloys (RHEAs), as a new class of HEAs have better mechanical properties at high temperatures than face-centered cubic (FCC) HEAs, and therefore have better prospects of application in the nuclear field. In this study, CSRO and its effect on the irradiation resistance of HfNbTaTiZr are analyzed via molecular dynamics (MD) and Monte Carlo (MC). The primary cascade simulations, multi-cascade simulations and surface bombardment simulations are carried out to simulate the generation and accumulation of irradiation damage. The results of the primary cascade simulations and surface bombardment simulations of CSRO models show that the presence of CSRO induces cascade splitting into subcascades. The presence of subcascades reduces the thermal peak enhancement effect and thus lowers the recombination rate of Frenkel pairs (FPs) in the damage zone when FPs concentrations are low. However, the creation of subcascades increases the size of the damage zone caused by the cascade. Thus, when the concentrations of FPs are high, the larger area of damage zone allows more of the already existing FPs to be included, thus promoting their recombination, i.e., impedes their accumulation when concentrations are high. These subcascades lower the recombination of FPs at low FPs concentrations but inhibit their accumulation at high FPs concentrations. The presence of CSRO is also beneficial in inhibiting the growth of point defect clusters, which further improves the resistance of HfNbTaTiZr to dislocation generation. Furthermore, the presence of CSRO facilitates the irradiation-induced phase transition. But it is found that HfNbTaTiZr shows suppression of HCP cluster growth. And the tendency to break down large HCP clusters into smaller ones is demonstrated in the CSRO model. From our calculations we also find that the irradiation-induced HCP atoms have a higher potential energy relative to the matrix. The potential energy difference between those energetic HCP atoms and the matrix can lead to generating a great number of insurmountable barriers pervading the matrix and largely suppressing the long-term mobility of FPs, thus limiting their aggregation and growth into clusters.

Tuning Corrosion Resistance and AC Soft Magnetic Properties of Fe-Co-Ni-Al Medium-Entropy Alloy via Ni Content

Corrosion of soft magnetic materials during service can significantly impact their performance and service life, therefore it is important to improve their corrosion resistance. In this paper, the corrosion resistance, alternating current soft magnetic properties (AC SMPs) and microstructure of FeCoNixAl (x = 1.0–2.0) medium-entropy alloys (MEAs) were studied. Corrosion resistance is greatly improved with an increase in Ni content. The x = 2.0 alloy has the lowest corrosion current density (Icorr = 2.67 × 10−7 A/cm2), which is reduced by 71% compared to the x = 1.0 alloy. Increasing the Ni content can improve the AC SMPs of the alloy. When x = 1.75, the total loss (Ps) is improved by 6% compared to the x = 1.0 alloy. X-ray diffraction (XRD) and scanning electron microscopy (SEM) show that the increase in Ni content is beneficial for promoting the formation of the face-centered-cubic (FCC) phase, and the body-centered-cubic (BCC) phase is gradually divided by the FCC phase. Electron backscatter diffraction (EBSD) shows that, with the increase in Ni content, the number of grain boundaries in the alloy is greatly reduced and numerous phase boundaries appear in the alloys. The degree of strain concentration is significantly reduced with the increasing Ni content. The corrosion mechanism of alloys is also discussed in this paper. Our study provides a method to balance the soft magnetic properties and corrosion resistance, paving the way for potential applications of Fe-Co-Ni-Al MEAs in corrosive environments.

Green Synthesis, Characterization and Antimicrobial Activities of Silver Nanoparticles against some Phypathogenic Bacteria

Green chemistry methods are now an intriguing field of study in agriculture, particularly in pest management. For this reason, novel approaches for the more efficient manufacturing of nanoparticles with improved biological characteristics have been developed. Because nanoparticle production is faster, this method is more eco-friendly and less toxic than old methods. The biosynthesis of silver nanoparticles (AgNPs) using Leucaena leucocephala, Mentha aquatica, and Zingiber officinale extracts and their antibacterial activity against Pectobacterium cartovorum, Agrobacterium tumefaciens, and Xanthomonas axonopodis. The results showed that spectroscopic and microscopic methods, such as UV-Vis spectroscopy, revealed absorption peaks for Ll-AgNPs at 415 nm, 420 nm for Ma-AgNPs, and 430 nm for Zo-AgNPs, indicating the silver nature of the prepared colloidal samples. The TEM images revealed the quasi-spherical morphology of NPs with an average size of 12.51, 10.63, and 10.26 nm for Ll-AgNPs, Ma-AgNPs, and Zo-AgNPs. The X-ray diffraction (XRD) pattern revealed a face-centered cubic (FCC) structure with crystallite. While distinctive peaks in an investigation using Fourier transform infrared (FT-IR) spectroscopy showed that several biomolecules were attached to AgNPs, antibacterial activity was evaluated by an inhibitory zone test, which showed high efficiency against P. cartovorum, A. tumefaciens, and X. axonopodis, with an antibacterial function comparable to L. leucocephala, M. aquatica, and Z. officinale extract. The green production of silver nanoparticles has the potential to be a useful tool in pest management strategies against phytopathogenic bacteria.

Post-processing of Inconel 718 superalloy by Laser-based Powder Bed Fusion: Microstructures and properties evaluation

In this work, IN718 superalloy has been additively manufactured through Laser-based Powder Bed Fusion (PBF) process. The present investigation aims to study the effect of post printing heat treatments on the metallurgical aspects, such as phases, crystallographic texture, microstructure evolutions and the mechanical properties. Heat treatment optimization has been pursued to achieve a better combination of strength and ductility. PBF fabricated material was further subjected to different heat treatments, comprising of homogenizing, solutionizing and ageing. Material was characterized with respect to the building direction (BD). As-printed specimen exhibits face centered cubic (FCC) γ matrix along with minor amounts of other phases. The melt pool boundaries were found to be rich in Niobium and Molybdenum, indicating segregation during fabrication. Upon post-heat treatments these segregations dissolved considerably. Heat treated microstructure exhibited homogeneously dispersed γ′ and γ′′ phases, and relatively small fractions of carbides, acicular and plate shaped δ phases. Heat treatments led to a significant increase in hardness (by about 54 %) and tensile strength (by about 45 %) while retaining considerable ductility.

Microstructure and mechanical properties of CuCrFeNi medium entropy alloys synthesized via mechanical alloying and spark plasma sintering

In this study, two novel Co-free medium entropy alloys (MEAs) with compositions of Cu20Cr10Fe35Ni35 (Cu20) and Cu10Cr20Fe35Ni35 (Cu10) were successfully prepared by a combination of mechanical alloying (MA) and spark plasma sintering (SPS). The Cu20 alloy exhibited a heterogeneous microstructure consisting of coarse and ultrafine grains (UFG) with a face-centered cubic (FCC) structure. In contrast, the Cu10 alloy showed a homogeneous UFG microstructure with an FCC matrix and a small amount of BCC phase. Moreover, both alloys contained a small amount of Cr7C3 particles, introduced by milling media during MA. In comparison with the Cu20 alloy, the Cu10 alloy exhibited better tensile properties, e.g., yield strength of 712 MPa, ultimate tensile strength of 843 MPa, and elongation of 20.1 %, demonstrating an excellent balance between strength and ductility compared to some well-established FCC-structured multi-component MEAs and high entropy alloys (HEAs). The enhanced tensile properties of the Cu10 alloy are attributed to the synergistic effects of grain refinement and Orowan strengthening by the fine Cr7C3 particles. The findings of this work provide valuable insights for designing cost-effective HEAs and MEAs with high strength and desirable ductility for various structural applications.

Grain-scale microtribological behavior of VCoNi medium-entropy alloy

The tribological behavior of equiatomic face-centered cubic (FCC) VCoNi medium-entropy alloy (MEA) remains underexplored despite of the alloy’s notable tensile strength and ductility. In this study, the tribological performance of VCoNi MEA is investigated using microscratching techniques, with emphasis on the effects of grain orientation, normal force, and scratch velocity. The study has demonstrated that the grain orientation in VCoNi MEA determines the activation of slip systems during the scratching processes, which significantly affects the morphology of wear tracks, slip steps and pile-up, as well as changes in microtribological behavior. As the normal force increases, the degree of wear intensifies, which is attributed to the significant material pile-up and more intense plastic flow. The plastic deformation of VCoNi MEA is found to be independent of scratch velocity within the 0.1–2 µm/s range. Ploughing and micro-shearing are identified as the primary wear mechanisms under various friction conditions. Furthermore, during the ploughing process, the deformation mechanism of the alloy is still dominated by dislocations. The direction of dislocation motion aligns with the direction of pile-up resulted from plastic deformation. The present study offers critical insights into the tribological behavior of medium-entropy alloys and broadens the potential for their applications in friction-intensive environments.

Reusability of Ti-6Al-4V powder in laser powder bed fusion: Influence on powder morphology, oxygen uptake, and mechanical properties

The reusability of Ti-6Al-4V powder in laser powder bed fusion (L-PBF) processes is essential for achieving economic efficiency and maintaining consistent product quality. While powder reuse offers clear cost benefits, it also raises concerns about preserving material quality and consistency across multiple build cycles. This study, therefore, investigates the effects of repeated powder reuse on key parameters, including powder morphology, oxygen uptake, and mechanical properties. The results demonstrate that the repeated reuse of the powder results in a decrease in satellite particles and an increase in particle deformation. Oxygen content progressively increases with each cycle; however, smooth particles maintain relatively stable oxygen levels, whereas rough particles exhibit a more pronounced rise in oxygen content. Mechanical testing shows that as oxygen levels increase, tensile strength improves, yet elongation decreases. This observed increase in strength can be partially attributed to oxygen-induced phase transformations, where localized oxygen enrichment promotes the formation of the face-centered cubic (FCC) β phase, contributing to material strengthening. These findings emphasize the importance of optimizing powder reuse strategies, particularly in controlling oxygen levels, to achieve the optimal balance between strength and ductility in high-quality material properties.

Improving electromagnetic wave absorption performance by adjusting the proportion of brittle BCC phase in FeCoNiCr0.4Mnx high-entropy alloys

High-entropy alloys, as a novel type of absorber, exhibit exceptional electromagnetic modulation capabilities and significant potential for electromagnetic wave absorption. In this work, the FeCoNiCrMn high-entropy alloy absorbent prepared through a mechanical alloying process demonstrates a dual-phase solid solution structure comprising face-centered cubic (FCC) and body-centered cubic (BCC) phases. By varying the manganese (Mn) content in the system, it is possible to enhance the degree of crystallinity, maintain the integrity of the crystal structure, and effectively control the relative proportion of the BCC phase within the overall phase composition. This adjustment improves the brittleness of the sheet-like particles, reduces particle size, and significantly lowers the permittivity. When the molar ratio of Mn is 0.6, the sample exhibits improved impedance matching due to the optimal permittivity and permeability. Notably, the impedance matching and attenuation constant can also be balanced. At 6.42 GHz, the FeCoNiCr0.4Mn0.6 alloy powder achieves the maximum reflection loss of −48.49 dB at a matching layer thickness of 3 mm. When the matching thickness is reduced to 2 mm, it can effectively cover a frequency range of 8.7–14.1 GHz (effective absorption bandwidth of 5.4 GHz), along with a wide absorption bandwidth and high absorption efficiency.

High-Entropy Alloy Laser Cladding with Cable-Type Welding Wire: Experimental Study and First-Principles Calculations

The Co-Cr-Fe-Ni high-entropy alloy (HEA) is particularly suitable for preparing coatings due to its excellent comprehensive properties. In this study, we use the laser cladding method to prepare Co-Cr-Fe-Ni HEA coatings with Co-Cr-Fe-Ni cable-type welding wire (CTWW) as the filling material and investigated the dilution rates of the coatings by experimental studies and first-principles calculations. The dilution rate is reduced to about 50% by changing the wire feeding speed, and a Co-Cr-Fe-Ni HEA coating with near nominal composition was prepared by multi-layer cladding. The HEA coating with near nominal composition is successfully prepared in the fourth layer of cladding. The coating is dense and uniform, with good metallurgical bonding. The mechanical properties of the coating were explored using first-principles calculations. All four coatings exhibit a single face-centered cubic (FCC) phase with good mechanical stability in the ground state. The bulk modulus B, shear modulus G, and Young’s modulus E of the four layers of coatings are gradually decreasing from B = 202 GPa, G = 136 GPa, and E = 334 GPa to B = 239 GPa, G = 154 GPa, and E = 380 GPa. The brittleness of the coating shows a trend of first decreasing and then increasing, and the coating closest to the nominal composition has the highest brittleness.

Brownian dynamics simulation of the structural evolution in monodisperse hard-sphere suspensions during drying and sedimentation processes.

The drying behavior of monodisperse colloidal films, with a focus on the influence of process variables on film microstructures, is explored via Brownian dynamics (BD) simulations. In our model, hard-sphere colloidal particles are dispersed in a Newtonian liquid with an initial particle volume fraction of 0.1. The effects of the drying rate and sedimentation on the evolving microstructures are systematically investigated using two dimensionless numbers: the Péclet number (Pe), which represents the competition between evaporation and diffusion, and the sedimentation number (Ns), which reflects the relative influence of sedimentation on evaporation. First, we analyze the local particle volume fraction and film structure at various Pe and Ns. As Pe increases, particle accumulation occurs near the liquid-gas interface, whereas a high Ns promotes dense packing near the substrate owing to sedimentation. The BD simulation results, viz. the local volume fraction profiles and drying regime maps, are in good agreement with those of the continuum model proposed by Wang and Brady. Structural analysis of the dried films reveals that at a low Pe (Pe = 0.1), a face-centered cubic (FCC) structure dominates, primarily independent of the sedimentation effects. In contrast, a high Pe leads to hexagonal close-packed or amorphous structure formation. Notably, at intermediate drying rates (Pe = 10), an increase in Ns promotes additional FCC ordering in the final film structure. Our study provides new insights into the hitherto underexplored role of sedimentation in the structural evolution of drying colloidal films, revealing the mechanisms of drying-induced assembly in colloidal systems.

Strengthening of HCP metals with split basal texture through non-dislocation hardening mechanism

Work hardening mechanisms in metals have been extensively studied with a focus on the motion of dislocations and their inhibition, and these studies have provided in-depth knowledge of the relationship between dislocations and work hardening; however, other factors also influence the work hardening mechanism. When polycrystalline metals deform, the shape of the grain boundaries must match between neighboring grains, resulting in deformation constraint between the grains. Hexagonal close-packed (HCP) single crystals exhibit greater plastic anisotropy than those in body-centered cubic (BCC) and face-centered cubic (FCC) crystals, leading to stronger deformation constraint between grains in polycrystalline HCP metals. This study investigates the effects of deformation constraint between grains on macroscopic stress–strain curves by reproducing the deformation of HCP metals using crystal plasticity finite element analysis. The results indicate that in polycrystalline HCP metals, the non-dislocation effect, constraint between grains, also significantly affects work hardening.

Influence of Cold Drawing on Phase Transformation and Tensile Properties of FeCrMn Austenitic Stainless Steel 201

Manganese stabilizes the austenite and reduces the stacking fault energy in face‐centered cubic (FCC) structures, promoting the formation of hexagonal and cubic structures. This study investigates the phase transformation and mechanical behavior of extremely low‐carbon FeCrMn austenitic stainless AISI 201 steel subjected to cold drawing in three stages, ultimately reaching a true strain of 0.93. The objective is to examine the transformation from the parent FCC structure to hexagonal close‐packed and body‐centered cubic structures as a combination of transformation‐induced plasticity and twinning‐induced plasticity phenomena. X‐ray diffraction and electron backscatter diffraction analyses are utilized to investigate phase transformations under significant plastic deformation and the crystallographic orientation relationships between phases. Additionally, tensile and hardness tests are performed to assess the impact of plastic deformation on mechanical properties. Results indicate that a true strain of 50% is optimal for balancing strength and ductility in CrMnFe austenitic stainless steel. After applying a true strain of ε1 = 26.7%, yield strength (YS) increases by 192% and ultimate tensile strength (UTS) by 35%, while elongation reduces by 41%. With a further strain of ε2 = 57.5%, YS increases by 71% and UTS by 44%, but elongation drastically decreases by 94%. Applying the final strain of ε3 = 94.0%, YS and UTS only increase by 3% and 2%, respectively, while elongation further reduced by 40%. These findings suggest that a true strain of 50% shall be considered the maximum reduction for maintaining a balance between strength and ductility in CrMnFe austenitic stainless steel.

Effect of Fe content on microstructure and mechanical properties of Fex(CoCrNi)100-x medium-entropy alloys

The high cost of high- and medium-entropy alloys (H/MEAs) has limited their structural applications, leading to increased interest in cost-effective ferrous MEAs (Fe-MEAs), where microstructure and mechanical properties are strongly influenced by Fe content. In this study, we systematically investigated the microstructural evolution, mechanical properties and deformation mechanisms of Fex(CoCrNi)100-x (x = 25, 40, 50, 62, 64, 66, and71, at.%) MEAs. The results revealed that the constituent phases evolved from a single face-centered cubic (FCC) phase (Fe25, Fe40, and Fe50) to a mixture of FCC and body-centered cubic (BCC) phases (Fe62, Fe64, and Fe66), eventually forming a single BCC phase (Fe71). As the Fe content increased, the yield strength (YS) gradually decreased from ∼394.8 MPa for Fe25 to ∼206.0 MPa for Fe62, while the uniform elongation (UE) remained above 40 % for all alloys. Further increases in Fe content significantly enhanced strength, though at the cost of a substantial reduction in elongation. Fe71 exhibited a high YS of ∼831.0 MPa but with a UE of only ∼1.5 %. In addition to dislocation slip, deformation nanotwins (DTs) were observed in deformed Fe50, and deformation-induced martensitic transformation (DIMT) was detected in deformed Fe64.

Enhancing fatigue resistance of Cr-Mn-Fe-Co-Ni multi-principal element alloys by varying stacking fault energy and sigma (σ)-phase assisted grain-size reduction

This study investigates two key aspects of the low cycle fatigue (LCF) behavior of alloys from the Cr-Mn-Fe-Co-Ni system at room temperature: (1) the influence of stacking fault energy (SFE) in single-phase face-centered cubic (FCC) alloys and (2) a grain size reduction triggered by the precipitation of a small amount of σ-phase. The first effect is investigated using model alloys (Cr26Mn20Fe20Co20Ni14 and Cr14Mn20Fe20Co20Ni26 in at.%, grain size: ∼60 µm), which have distinct SFEs at room temperature. A reduction in SFE from 69 to 23 mJ/m2 results in a 10 to 20 % increase in tensile/compressive peak stresses, i.e., cyclic strength, across all examined strain amplitudes (±0.3 %, ±0.5 %, and ±0.7 %) while maintaining comparable fatigue lives. Despite its higher cyclic strength, the low-SFE alloy exhibits delayed, and less evolved dislocation substructures than the other alloy. In both single-phase alloys, fatigue cracks originated from the surface reliefs, surface-exposed coherent annealing twin boundaries, and occasionally from high-angle grain boundaries. However, the crack propagation rate was slower in the low-SFE alloy, contributing to its superior fatigue resistance. By aging the low-SFE Cr26Mn20Fe20Co20Ni14 alloy differently, we could induce the precipitation of ∼5 % σ-phase during recrystallization, which strongly reduced the FCC grain size to ∼5 µm. With this microstructure, the cyclic strength increased by 50–65 % and remained more stable during fatigue testing while maintaining a comparable life. The σ-precipitates were found to deflect and arrest fatigue cracks, while extensive deformation twinning around cracks complements slip activity and reduces crack propagation rate. Overall, the σ-phase-assisted grain size reduction is 3 to 5 times more effective in improving cyclic strength than SFE reduction.

SILVER NANOPARTICLES-AQUEOUS LEAF EXTRACT OF SIDAGURI (SIDA RHOMBIFOLIA) AS REDUCING AGENTS

The Sidaguri leaf, scientifically known as Sida rhombifolia, is a plant species rich in flavonoids that have the ability to act as reducing agent in formation of silver nanoparticles. This study presented the synthesis of silver nanoparticles (AgNp-Sid) using aqueous leaf extract of sidaguri. This study utilized a concentration ratio of 2:90 mL aqueous leaf extract of Sidaguri and AgNO3 1 mM. The size and morphology of AgNp-Sid was measured using UV-Visible Spectrophotometer, PSA, FT-IR, SEM-EDS, and XRD. The investigation revealed an ordinary particle size of 63.5 nm with polydispersity index (PI) of 0.284. The maximum wavelength varies between 405.4 nm and 407.8 nm with the increasing of time. AgNp-Sid exhibited a spherical morphology and had a crystalline structure that is face-centered cubic. The results suggested that the aqueous leaf extract of sidaguri had the ability to function as a reducing agent in the synthesis of silver nanoparticles, offering a safe, cost-effective, and environmentally friendly alternative.