Interstitial Alloys Research Articles

Elastic Deformation and Elastic Wave Velocity for Cubic Metal and Binary Interstitial Alloy’s Thin Films at Different Temperatures, Pressures, Interstitial Atomic Concentrations and Film Thicknesses

Elastic Deformation and Elastic Wave Velocity for Cubic Metal and Binary Interstitial Alloy’s Thin Films at Different Temperatures, Pressures, Interstitial Atomic Concentrations and Film Thicknesses

The Structure Evolution of the Interstitial High Entropy Alloy Fe50Mn30-xCr10Ni10Cx Produced by Mechanical Alloying

The Structure Evolution of the Interstitial High Entropy Alloy Fe50Mn30-xCr10Ni10Cx Produced by Mechanical Alloying

Additive Manufacturing of Interstitial Nitrogen‐Strengthened CoCrNi Medium Entropy Alloy

Equiatomic CoCrNi medium entropy alloy (MEA) is known for its excellent mechanical properties, oxidation resistance, and hydrogen embrittlement resistance. Interstitial elements like carbon and nitrogen further enhance these properties. However, there is limited research on interstitial solid solution‐strengthened alloys produced via powder bed fusion‐laser beam (PBF‐LB). This study investigates the role of nitrogen as an interstitial alloying element in CoCrNi MEA using PBF‐LB. Two alloy variants, one without nitrogen and one prealloyed with nitrogen, are analyzed through thermodynamic calculations and experimental validations. A minor nitrogen loss occurs in as‐printed samples compared to prealloyed powders, but the remaining nitrogen stays as an interstitial solid solution without forming detrimental secondary phases. This leads to improved mechanical properties, with yield and ultimate tensile strengths increasing from about 690 and 900 MPa in nitrogen‐free samples to over 750 and 1000 MPa in nitrogen‐containing samples while maintaining the high ductility of the nitrogen‐free counterpart in the as‐printed materials. Additionally, the nitrogen‐containing CoCrNi‐N MEA exhibits ≈35HV higher hardness than the nitrogen‐free variant in both as‐printed and heat‐treated states. These findings highlight the benefits of nitrogen addition in enhancing the mechanical properties of CoCrNi MEA produced by PBF‐LB.

Crystal-Phase- and B-Content-Dependent Electrochemical Behavior of Pd─B Nanocrystals toward Oxygen Reduction Reaction.

The manipulation of crystal phases in metal-nonmetal interstitial alloy nanostructures has attracted considerable attention due to the formation of unique electronic structures and surface atomic arrangements, resulting in unprecedented catalytic performances. However, achieving simultaneous control over crystal phase and nonmetal elements in metal-nonmetal interstitial alloy nanostructures has remained a formidable challenge. Here, a novel synthesis approach is presented for Pd─B interstitial alloy nanocrystals (NCs) that allows investigation of the crystal-phase- and B-content-dependent catalytic performance. Through comparison of the oxygen reduction reaction (ORR) properties of Pd─BX interstitial alloy NCs with different crystal phases and B contents, achieved by precise control of reaction temperature and time, the influences of crystal phase and B contents in the Pd─BX interstitial alloy NCs on ORR are precisely investigated. The hexagonal closed packed (hcp) PdB0.5 NCs exhibit superior catalytic activity, with mass activities reaching 2.58 A mg-1, surpassing Pd/C by 10.3 times, attributed to synergistic effects by the hcp crystal phase and relatively high B contents. This study not only provides a novel approach to fabricate interstitial alloy nanostructures with unconventional crystal phases and finely controlled nonmetal elements but also elucidates the importance of crystal phase and nonmetal element content in optimizing electrocatalytic efficiency.

STUDY ON SELF-DIFFUSION IN ALLOY AuCuSi WITH FCC STRUCTURE: DEPENDENCE ON TEMPERATURE, PRESSURE, CONCENTRATION OF SUBSTITUTIONAL ATOMS, CONCENTRATION OF INTERSTITIAL ATOMS AND STRAIN

This article presents a self-diffusion theory, including analytical expressions for activation energy, pre-exponential factor, and self-diffusion coefficient, dependent on temperature, pressure, the concentration of substitutional atoms, the concentration of interstitial atoms, and strain for substitutional and interstitial ternary alloys with the FCC structure, based on the statistical moment method (SMM). The theoretical results are applied to numerical calculations for the AuCuSi alloy. The SMM numerical results for AuCuSi are compared with those for AuSi, AuCu, and Au. The variation of self-diffusion quantities with temperature and strain in AuCuSi follows the same patterns as in AuCu, AuSi, and Au. The variation with the interstitial atom concentration in AuCuSi follows the same pattern as in AuSi, while the variation with the substitutional atom concentration follows the same pattern as in AuCu. The SMM numerical results for Au's self-diffusion quantities agree well with experimental data and other calculation results. Other SMM numerical results for self-diffusion quantities are novel and predict future experimental outcomes.

Anion-modulated HER and OER activity of 1D Co-Mo based interstitial compound heterojunctions for the effective overall water splitting

Anion-modulated HER and OER activity of 1D Co-Mo based interstitial compound heterojunctions for the effective overall water splitting

Topological Photonic Alloy.

We present the new concept of photonic alloy as a nonperiodic topological material. By mixing nonmagnetized and magnetized rods in a nonperiodic 2D photonic crystal configuration, we realized photonic alloys in the microwave regime. Our experimental findings reveal that the photonic alloy sustains nonreciprocal chiral edge states even at very low concentration of magnetized rods. The nontrivial topology and the associated edge states of these nonperiodic systems can be characterized by the winding of the reflection phase. Our results indicate that the threshold concentrations for the investigated system within the first nontrivial band gap to exhibit topological behavior approach zero in the thermodynamic limit for substitutional alloys, while the threshold remains nonzero for interstitial alloys. At low concentration, the system exhibits an inhomogeneous structure characterized by isolated patches of nonpercolating magnetic domains that are spaced far apart within a topologically trivial photonic crystal. Surprisingly, the system manifests chiral edge states despite a local breakdown of time-reversal symmetry rather than a global one. Photonic alloys represent a new category of disordered topological materials, offering exciting opportunities for exploring topological materials with adjustable gaps.

Advanced interstitial high-entropy alloy engineered for exceptional wear resistance via dual nanoprecipitation-induced heterogeneous structure

Despite achieving notable strength and wear resistance in precipitation-strengthened Cantor high-entropy alloy (HEA), the inherent brittleness of precipitates leads to a loss of ductility. In this study, we propose a novel approach to address this issue by introducing nanosized M23C6-combined with Cr2N, termed dual-nanoprecipitation, and heterogeneous structure in a C and N co-doped interstitial HEA (iHEA). The abundant nanoscale M23C6 and Cr2N particles serve not only as reinforcing agents to enhance strength and wear resistance but also hinder the recrystallization process, resulting in a heterogeneous structure containing recrystallized and non-recrystallized zones. This heterogeneity triggers additional strengthening and strain hardening mechanisms, thereby enhancing the deformability of iHEA. Furthermore, the heterogeneous structure effectively mitigates strain localization on the sliding surface during wear, thus improving tribological properties. By overcoming the challenge of poor ductility while maintaining exceptional strength and wear resistance, the dual-nanoprecipitation-induced heterogeneous structure offers promising avenues for the development of alloys with superior strength-ductility synergy and wear resistance.

Revealing the Superior Post-Necking Elongation in the Fine-Grained Ti-6Al-4V ELI at Cryogenic Temperature

The mechanical properties of a fine-grained (FG) Ti-6Al-4V extra-low interstitial (ELI) alloy were investigated by tensile tests at 298 K and 77 K. The experimental results indicated that, at 77 K, the alloy exhibits a small uniform elongation of 2.65%, but has a fracture elongation of 19.2%, showing superior post-necking elongation. At 298 K, the alloy displays a single dislocation slipping, β→α″ phase transformation occurred, and 6.35% uniform elongation was obtained, whereas the coupling of dislocation slipping and twinning deformation behaviors dominated at 77 K. The limited uniform elongation is attributed to the absence of martensite phase transformation at 77 K, whereas the decent fracture elongation is ascribed to the resistance offered by twinning against plastic instability.

Study of the structure and properties of interstitial alloys TixMo1 – xCyNz

Developing the new materials with improved properties suggests study of the crystal structure and properties of multicomponent interstitial alloys. We present the results of studying the crystal structure and microhardness of TixMo1 – xCyNz interstitial alloys in massive samples with different ratios of concentrations of constituent elements. The samples obtained by self-propagating high-temperature synthesis were subjected to homogenizing annealing at 2600 K for 8 h and cooled together with the furnace. Data of neutron diffraction revealed that the alloys have a face-centered cubic crystal structure in which Ti and Mo atoms, as well as C and N, are intersubstituted and statistically located in the 4b positions and octahedral 4a positions, respectively. The Rietveld method was used to determine crystallite sizes, dislocation densities, and microstrain using X-ray diffraction patterns. The microhardness of the samples was determined by the Vickers method. It is shown that the crystallite sizes determined by the Williamson-Hall and Scherrer methods differ significantly, whereas the patterns of crystallite growth in size, as well as regularities of changes in the dislocation density and microstrains follow change in the concentration of the components in the composition. As the carbon content in the alloy increases, the crystallite sizes and microstrains decrease, and the dislocation density increases. It is revealed that the smaller the crystallite size and the higher the dislocation density, the more microhardness is displaced towards increasing the carbon content. With a change in the ratio of components in TixMo1 – xCyNz as the crystallite size and microstrains decrease and dislocation density increases, the microhardness of the alloy increases by 1.5 – 2 times compared to binary carbide and titanium nitride. The results obtained can be applied to the use of interstitial alloys in instrumental and high-temperature engineering.

Processing of High Interstitial Austenitic Steel with Powder Bed Fusion‐Laser Beam/Metal: Evolution of Chemical Inhomogeneity and Microstructural Features during Postprocessing

Powder bed fusion‐laser beam/metal (PBF‐LB/M) additive manufacturing provides a high potential to overcome the poor machinability of nickel‐free high interstitial alloy austenitic (HIA) steels. Therefore, this study focuses on the PBF‐LB/M processability of HIA X40MnCrMoN21‐18‐2 and the effect of postprocessing on microstructure and chemical homogeneity. Samples are fabricated on a laboratory and industrial PBF‐LB/M machine and subsequently postprocessed by conventional solution annealing or hot isostatic pressing (HIP). The influence of the processing steps on the microstructure and on the chemical composition is evaluated by scanning electron microscopy, X‐ray diffraction, transmission electron microscopy, atom probe tomography, and electron backscatter diffraction. The commercially available HIA powder exerts good processability, both by optimized and predefined PBF‐LB/M parameters. Loss of Mn and N is detected after PBF‐LB/M processing. Chemical homogenization but no further change in composition occurs during postprocessing. The as‐built microstructure shows segregation of elements (N, Mo, Cr, Mn) in intercellular spaces. A thermodynamic calculation confirms that N approaches a para‐equilibrium state in the PBF‐LB/M as‐built condition, while C does not. Porosity can be reduced by thermomechanical posttreatment with HIP. At the same time, HIP partially recrystallizes the microstructure, while (Mn + Cr)2SiO4 type oxides delay recovery and recrystallization of the microstructure.

Mechanical properties and deformation mechanisms of C-doped interstitial high-entropy alloy CrMnFeCoNi: Effects of strain rate and C content

The effects of strain rate on mechanical properties, microstructural evolution and underlying deformation mechanisms of two kinds of interstitial CrMnFeCoNi high entropy alloys (HEAs), (CrMnFeCoNi)99.5C0.5 and (CrMnFeCoNi)99.0C1.0, are investigated under quasi-static and dynamic tension. Dynamic loading is carried out via a split Hopkinson tension bar system. The pre- and post-deformation microstructures are characterized with electron back scatter diffraction and transmission electron microscopy. Both yield strength and work hardening increase remarkably with increasing strain rate. Plastic deformation in both alloys under quasi-static and dynamic loading are dominated by dislocations, stacking faults, kink bands and deformation twins. Twinning is activated easier under dynamic loading, and twin density decreases with increasing carbon content due to the increased stacking fault energy. The Khan-Liu constitutive model can describe the experimental results for these two interstitial HEAs in a wide strain range.

Combined effect of interstitial-substitutional elements on dislocation dynamics in nitrogen-added austenitic stainless steels

Combined addition of interstitial-substitutional elements has been acknowledged to contribute to the increase in the strengths of steels. For further improvements in mechanical properties, their atomic-scale interaction mechanisms with dislocations are required to be examined. In this study, both high-resolution transmission electron microscopy and atom-probe tomography were used to correlate interstitial-substitutional elements with dislocation characteristics in austenitic stainless steels. Three types of dislocation core structures are identified and associated with their strain fields as well as N and Cr atoms in the N-added steels. It is revealed that N atoms interact elastically with the dislocations, followed by the segregation of Cr atoms via the chemical interaction between N and Cr atoms. This insight significantly improves the understanding of the multiple alloying mechanism in metallic materials such as interstitial alloys and high-entropy alloys.

Monometallic Ultrasmall Nanocatalysts via Different Valence Atomic Interfaces Boost Hydrogen Evolution Catalysis.

Synergistic monometallic nanocatalysts have attracted much attention due to their high intrinsic activity properties. However, current synergistic monometallic nanocatalysts tend to suffer from long reaction paths due to restricted nanoscale interfaces. In this paper, we synthesized the interstitial compound N-Pt/CNT with monometallic atomic interfaces. The catalysts are enriched with atomic interfaces between higher valence Ptδ+ and Pt0, allowing the reaction to proceed synergistically within the same component with an ideal reaction pathway. Through ratio optimization, N2.42-Pt/CNT with a suitable ratio of Ptδ+ and Pt0 is synthesized. And the calculated turnover frequency of N2.42-Pt/CNT is about 37.4 s-1 (-0.1 V vs reversible hydrogen electrode (RHE)), six times higher than that of the commercial Pt/C (6.58 s-1), which is the most intrinsically active of the Pt-based catalysts. Moreover, prepared N2.42-Pt/CNT exhibits excellent stability during the chronoamperometry tests of 200 h. With insights from comprehensive experiments and theoretical calculations, Pt with different valence states in monometallic atomic interfaces synergistically accelerates the H2O dissociation step and optimizes the Gibbs free energy of H* adsorption. And the existence of desirable hydrogen transfer paths substantially facilitates hydrogen evolution reaction kinetics.

Excellent strength-ductility combination of interstitial non-equiatomic middle-entropy alloy subjected to cold rotary swaging and post-deformation annealing

The effect of cold rotary swaging and subsequent annealing on the microstructure, texture and mechanical properties of a Fe49.5Mn30Co10Cr10C0.5 middle-entropy alloy was studied. Finite element modeling predicted inhomogeneous stress distribution and temperature gradient during deformation. Microstructure analysis indicated the development of deformation-induced γ→ε martensitic transformation during earlier steps of cold rotary swaging (20–40 % reduction). However, a single-phase face-centered cubic structure was attained after 60–90 % reduction due to reverse ε→γ transformation. Meanwhile, a twin-matrix microstructure was observed in the bar center, whereas an ultrafine microstructure was formed at the bar edge. Post-deformation annealing at 600 °C caused the onset of static recrystallization and thereby the formation of ultrafine dislocation-free grains. Apparently, after 60–90 % reduction, a ⟨100⟩- and ⟨111⟩-fiber texture gradient along the bar cross-section was developed. Besides, at the bar edge, a pronounced B/B‾ shear texture was obtained that transformed into a Cube texture after annealing at 700 °C. Compared to the as-swaged material (yield strength (YS) = 1250 MPa; ultimate tensile strength (UTS) = 1520 MPa; elongation to failure (EF) = 6.5 %), annealing at 500 °C resulted in additional strengthening (YS = 1655 MPa; UTS = 1660 MPa), but EF did not change noticeably. Yet, annealing at 600°С was accompanied by an essential increase in both EF (to 11 %) and YS (to 1500 MPa). The applied approach can be used for obtaining a material with an attractive strength-ductility combination due to overcoming the strength-ductility trade-off.

Effect of annealing temperature on the microstructure evolution and corrosion behavior of Carbon-interstitial FeMnCoCrNi high-entropy alloys

The microstructure evolution, corrosion resistance, and passive-film properties of an interstitial FeMnCoCrNi high-entropy alloys annealed at different temperature were investigated. Deformation twins, Strip-shape and ellipsoidal M23C6 carbides are remained within grains and precipitated along the grain boundaries of the HEAs annealed at 500 and 700 °C. The 900 °C annealed i-Cantor alloys are fully recrystallized without deformation twins and precipitated with round M23C6 carbides. The corrosion resistance of the cold-rolled HEAs was deteriorated by annealing at 500 and 700 °C, but improved by annealing at 900 °C, which decreases the dislocation densities and depresses the Cr-depleted regions in i-Cantor alloys.

PVD Coatings as Protective Films in Fashion Industry

Modification of surface properties with the purpose of improving resistance, hardness, and endurance is a common practice in most industrial applications. However, the fashion industry has a more complex goal of meeting customers' aesthetic tastes while maintaining quality and mechanical properties with safety characteristics. The use of galvanic coatings on metal substrates allows for a good compromise among all these requirements, but toxic solvents combined with nickel and chromium(VI) baths heavily impact the environment and human health. For this reason, alternative approaches have been studied, and we propose Physical Vapor Deposition (PVD) coatings as a good alternative.The objective of this study is to develop protective coatings in Cr/CrN for brass substrates using the PVD technique. PVD is an mature and very stable technique, the use of which was limited until now by the high costs of the vacuum system and targets. The environmental impact of PVD is very low, and a wide range of coatings with elevated purity can be prepared, such as metallic, ceramic, nitrides, and oxides.Brass substrate is commonly used in the manufacturing industry because of some interesting properties, such as ductility, resistance, and a low melting point, which allows for low-temperature processing and low costs. However, brass is known to have inadequate corrosion resistance, which negatively impacts the quality of the final products. For this reason, there is a need to look for coatings that improve the corrosion resistance of brass, keeping a shiny and smooth aspect with desirable colors.Chromium Nitride is an extremely hard, inert, thin film that is applied primarily to precision metal parts. CrNx also performs well in corrosive environments and in sliding wear applications. Precisely, CrNx is an interstitial compound with nitrogen atoms occupying the octahedral holes in the chromium lattice. This characteristic opens the door to interesting investigations: by modifying the chamber pressure and N2/Ar flow, one can obtain films with different stoichiometry. In this study, five thin films of 350 nm of Cr/CrN were prepared by changing the ratio of N2/Ar in the chamber from 0.2 to 0.6. Using Scanning Electron Microscopy (SEM), we investigated the homogeneity of the coatings and estimated the percentage of defects formation. The chemical composition was analyzed with Energy Dispersive X-ray Spectroscopy (EDS-SEM), while the color coordinates were estimated with a Spectrophotometer. In parallel, we investigated the thickness and structure combining SEM with XRF technique [1]. As a result of this study, we selected the 0.4 ratio N2/Ar for CrNx layers, which agreed with literature [2], and created a multilayer film of Cr/CrN. Finally, we tested different combinations of engineered multilayer films with electrochemical tests such as free corrosion test OCP, Electrochemical Impedance Spectroscopy (EIS), and neutral salt spray (NSS) test (ISO 9227:2017). Then, we compared the results to understand and optimize which condition combinations are more suitable for protective applications. In conclusion, by deepening the knowledge on this topic, it might be possible to play with the pressure conditions in the chamber to open new design possibilities.

Extensive Experimental Thermal Runaway and Thermal Propagation Characterization of Large-Format Tabless Cylindrical Lithium-Ion Cells with Aluminum Housing and Laser Welded Endcaps

Large-format tabless cylindrical lithium-ion cells are expected to enhance performance and reduce cost of next generation vehicles. The influence of innovative new tab designs, increased dimensions and new housing materials are however still unexplored and must be revealed to unlock safe future battery systems. In this study, the thermal runaway and thermal propagation characteristics of sophisticated state-of-the-art large-format tabless cylindrical cells with aluminum housing and laser welded endcaps are extensively characterized. Multiple abuse test setups on cell and battery level are custom designed close to the true boundary conditions in real world applications. Results show cells with aluminum housing require careful choice of trigger methods as the low melting point and less mechanical strength compared to conventional nickel-plated steel housings introduce additional challenges. The tabless design was found to act as a strong mechanical connection that prevents shifting of the electrode assembly. Instead, axial ruptures of the jelly roll may occur. The leftover high density material conglomeration that is in tight contact with the inner housing wall transfers heat into the surroundings and is critical for thermal propagation safety. Strong interstitial potting compound with low thermal conductivity successfully prevented any major convective heat transfer into the neighboring cells by venting gas.

Microstructural evolution and deformation behavior of an interstitial TRIP high-entropy alloy under dynamic loading

The mechanical properties and microstructural evolution under dynamic loading conditions are of paramount importance in the development and utilization of interstitial high-entropy alloys (iHEAs). This study focuses on the investigation of a currently trending material, C-doped TRIP-assisted HEA Fe49.5Mn30Co10Cr10C0.5 (at.%). By subjecting the alloy to uniaxial quasi-static and dynamic tensile loading, the study systematically elucidates mechanical property testing under different strain states, characterizes the microstructural evolution during deformation, analyzes deformation mechanisms, and delves into the essence of mechanical responses. Particularly, by employing digital image correlation (DIC) techniques, local severe deformation regions under high-speed deformation conditions are sampled to investigate microstructural changes under extreme deformation conditions. The results indicated that, in comparison to quasi-static tensile deformation, the dynamic tensile deformation of the HEA demonstrated a slight increase in yield strength, a decrease in ultimate tensile strength, and a trend toward an increase in total elongation. Specifically, at a strain rate of 103 s−1, the tensile strength was ∼825.5 MPa, and at a strain rate of 10 s−1, the elongation was ∼57.7 %. In quasi-static deformation, the TRIP and TWIP effects served as the primary deformation mechanisms. In dynamic deformation, the proportion of ε-martensite phase transformation was significantly reduced, with deformation twinning (DT) and dislocations becoming the dominant mechanisms, originating from the impact of adiabatic heating on the stacking fault energy (SFE). Furthermore, in the locally severe deformation region, multiple twinning systems were activated, coupled with a substantial accumulation of dislocations. A minor presence of dual-oriented martensite also contributed to this complex mechanism. Additionally, the carbides formed through C-doping exerted a significant hindrance on dislocation slip during high-speed deformation and under high-strain conditions. Simultaneously, they promoted the activation of multiple twinning systems, making an indispensable contribution to maintaining the strain hardening rate (SHR) of the HEA.

Hydrogen-assisted fatigue crack propagation behavior of a C–N co-doped interstitial high-entropy alloy

The hydrogen-assisted fatigue crack propagation behavior of a C–N co-doped interstitial high-entropy alloy (iHEA) was investigated under in-situ electrochemical hydrogen charging. The cracking path, deformation microstructure, and fractography were characterized via multiple methods. Results suggest that hydrogen uptake shows a certain acceleration on the fatigue crack propagation rate (FCGR) of the iHEA, and such acceleration increases are intensified when increasing the hydrogen-charging current density. Crack propagation along grain boundaries and a remarkable decrease in the extent of plastic deformation immediately near to the crack surface have also been observed. This decrement of critical plastic strain for fatigue crack propagation primarily accelerates the FCGR.