Diffusion Of Fe Atoms Research Articles

Understanding the influence of hydrogen on BCC iron grain boundaries using the kinetic activation relaxation technique (k-ART)

Abstract Hydrogen embrittlement (HE) poses a significant challenge to the mechanical integrity of iron and its alloys. This study explores the influence of hydrogen atoms on two distinct grain boundaries (GBs), $\Sigma37$ and $\Sigma3$, in body-centered-cubic (BCC) iron. Using the kinetic activation relaxation technique (k-ART), an off-lattice kinetic Monte Carlo approach with an EAM-based potential, extensive catalogs of activated events for atoms in both H-free and H-saturated GBs were generated.
Studying the diffusion of H, we find that, for these systems, while GB is energetically favorable for H, this element diffuses more slowly at the GBs than in the bulk. The results further indicate that the $\Sigma 3$ GB exhibits higher stability in its pure form compared to the $\Sigma 37$ GB, with notable differences in energy barriers and diffusion behaviors. Moreover, with detailed information about the evolution landscape around the GB, we find that the saturation of a GB with hydrogen both stabilizes the GB by shifting barriers associated with Fe diffusion to higher energies and reducing the number of diffusion events. For the $\Sigma 37$ GB, the presence of hydrogen causes elastic deformation, affecting the diffusion of Fe atoms both at the GB and in adjacent positions. This results in new diffusion pathways but with higher diffusion barriers, unlike for the $\Sigma 3$ GB. These results indicate that the presence of hydrogen rigidifies the direct GB interface layers while allowing more atoms to be active for the $\Sigma 37$ GB. This provides a microscopic basis to support the existence of competing mechanisms compatible with either plasticity (such as hydrogen enhanced localized plasticity --- HELP) or energy-dominated (hydrogen enhanced decohesion mechanism ---HEDE) embrittlement, with the relative importance of these mechanisms determined by the local geometry of the GBs.

Enhancement in Corrosion Resistance of Low-Carbon Steel via Surface Modification

This research investigated the corrosion resistance of surface layers on low-carbon steel exposed to a chloride environment at room temperature. This study systematically evaluated the effects of varying pack compositions, coating temperatures, and application durations on the characteristics of the deposited coatings. The potentiodynamic polarization corrosion test was employed to assess the wet corrosion behavior of the specimens. Elemental compositions and microstructural features were analyzed using energy-dispersive X-ray spectroscopy (EDX) in conjunction with scanning electron microscopy (SEM), providing insights into phase distribution. The chromizing, titanizing, and chromotitanizing treatments were conducted at temperatures of 900 °C, 1000 °C, and 1100 °C, respectively, with varying coating times. X-ray diffraction analysis revealed a complex arrangement of elements and compounds within the coatings, including Cr, Ti, Cr1.9Ti, FeTi, Al2O3, Cr2O3, TiO2, Cr1.36Fe0.52, and (Ti0.86)3.58. The study found that as the deposition duration increased, the coating thickness increased, comprising a thin inner layer and a substantially thicker outer layer. This layered structure resulted from the outward diffusion of Fe atoms and the inward diffusion of Cr and Ti atoms. Electrochemical analysis in a 3.5% NaCl aqueous solution indicated a marked enhancement in the corrosion resistance of the coated specimens compared to their uncoated counterparts. The potentiodynamic polarization tests confirmed that the protective coatings significantly reduced the corrosion rate, with performance influenced by both the temperature and duration of the deposition process. These findings highlighted the potential of tailored coating techniques to improve the durability and performance of low-carbon steel in corrosive environments.

Influence of minor Mg/Ca/Nb/Ag addition on the morphology and microstructure of Fe-rich phase in powder metallurgy Cu[sbnd]10Fe alloy

The effect of Mg/Ca/Nb/Ag alloying on the morphology and microstructure of powder metallurgy Cu10Fe alloy was investigated systemically in this work. Alloying of Ca reduces the size of Fe-rich particles, while alloying of Mg/Nb/Ag increases the Fe-rich particles. This is attributed to the different roles of various alloying elements on the liquid-phase separation behaviors as well as diffusion of Fe atoms during the solidification. Coarse size spherical Fe-rich particles with a face centered cubic structure are observed in CuFe alloys bearing Mg/Ag/Nb, whilst the alloying of Ca favors the formation of fine spherical Fe-rich particles with a body centered cubic structure. The factor governing the morphology is found to be interfacial energy for CuFe alloys containing Mg/Ag/Nb and elastic energy for Cu-Fe-Ca alloy, respectively. Coarse size Fe-rich particles are hard to deform during subsequent rolling, but the fine Fe-rich particles can co-deform with Cu matrix. This study could provide a detailed picture regarding the influence of various alloying element types on the size, morphology, and lattice structure of Fe phase of CuFe alloy.

Comparative studies on microstructural characteristics and wear behavior of high-speed and low-speed laser cladding graphene/CoCrFeMo0.5NiTi0.5 high-entropy alloy composite layers

To prevent the failure of curved parts due to wear under actual working conditions, a graphene/CoCrFeMo0.5NiTi0.5 high-entropy alloy composite coating was prepared on the surface of a curved part using both high-speed and low-speed laser cladding (LLC). The surface morphology, physical phases, elemental distribution, microstructure, microhardness, and wear behavior of this coating applied via high-speed and LLC were comparatively studied. The results showed that the maximum height difference on the surface of the high-speed laser cladding (HLC) layer was only 44.7 % of that of the LLC layer, and the surface powder was more completely melted. The average microhardness of the HLC layer was about 1.49 times higher than that of the LLC layer and showed a maximum hardness of 666.38 HV0.5, which was about 2.95 times higher than that of the substrate. The internal microstructure of the HLC layer was finer and the diffusion of Fe atoms from the substrate into the coating was significantly reduced. In all three wear environments, abrasive wear occurred in both the low-speed and HLC layers. The total wear rate of the LLC layer was 230.588 μm3 N−1 mm−1, which was about 3.06 times higher than that of the HLC layer (75.395 μm3 N−1 mm−1). The wear surfaces of both cladding layers were oxidized, and the wear rate increased with the oxygen content on the wear surfaces under the same wear conditions. Meanwhile, the oxygen content of the wear surfaces of both cladding layers in sodium chloride solution was significantly higher than that during dry wear.

Severe plastic deformation-induced rapid diffusion behavior at the Al/steel interface

The severe plastic deformation (SPD)-induced atom rapid diffusion joining method was employed to increase Al/Fe diffusion rate at short time and low temperature, and achieve reliable metallurgical bonding. The local stress and strain caused by SPD led to the refinement of crystal grains and the generation of high concentrations of dislocations, which provided channels for the rapid diffusion of Fe atoms to the Al interface region. The diffusion rate of the interface layer is 103 faster than the thermal activation diffusion state. The short-term and low-temperature characteristics of the SPD-induced rapid diffusion method can be extended to other solid-state welding methods.

Elucidation on the correlation between thermal stability of Al13Fe4 intermetallic phase and mechanical properties of the Al-Fe alloy fabricated via friction stir alloying

Al-Fe alloy containing nanosized Al13Fe4 phase was fabricated by the solid-state multiple pass friction stir alloying (FSA) technique and subjected to heat treatment at different time-temperature conditions. During annealing, the diffusion of Fe atoms leads to the necking and fragmentation of the coarse plate shape Al13Fe4 IMC phase resulting in its spheroidization. However, as the annealing time is extended, the spheroidized Al13Fe4 phase undergoes coarsening and grows predominantly along a specific plane. This growth process transforms the originally spherical shape into an elliptical or small plate-like morphology. The grain size was insignificantly affected by the annealing time and temperature owing to the grain boundary pinning by the nanometric-sized IMC phase. The ultimate tensile strength of the Al-Fe alloy (149 MPa) is improved significantly at the annealing conditions of 200 °C/4hrs (165 MPa), 200 °C/6hrs (167 MPa), and 300 °C/2hrs (163 MPa). The improved UTS is attributed to the increased isotropic work hardening owing to the reduced IMC particle size and mean interparticle spacing in the Al-Fe alloy. The lowest work hardening rate is observed in the specimen annealed at 200 °C for 2 hrs (largest particle size) which is attributed to the stored energy in the material due to severe plastic deformation (SPD) associated with the FSA. The correlation between the work hardening rate, IMC particle size, and mean interparticle spacing at various annealing conditions are established.

Interfacial reactions and joint performances of high-power ultrasonic welding of aluminum to steel

Aluminum and steel dissimilar sound joints were fabricated using a 4.0 kW high-power ultrasonic welder. The microstructure and mechanical properties of the joint resulting from high-power ultrasonic welding were investigated. To further understand the formation mechanism of the joint, macro and micro plastic deformation were also examined using the finite element method. As the welding duration increased to 0.4 s, the conversion of electrical power to heat flow at the interface also increased, with approximately 56% of the electrical power being transformed into the heat flow of the welding interface. The material flowed from the center of the welding interface and accumulated at the edge, resulting in a welding area measuring 9 mm × 7 mm, significantly larger than the sonotrode tip area. The plastic strain in the welding zone reached 3.7, with the aluminum side exhibiting higher plastic strain than the steel side, facilitating Fe atom diffusion towards aluminum. The intermetallic compound (IMC) primarily consisted of FeAl3 and Fe2Al5. The joint strength increased significantly as the thickness of the IMC increased. However, when the IMC thickness exceeded 1.7 μm, the joint strength decreased. Through interfacial metallurgical reactions and intense mechanical interlock, joints with a lap-shear strength of 62.7 MPa were achieved. The fracture mode of the joint was a ductile-brittle hybrid fracture.

Effect of Mg and Si contents on hot-dip 55Al-Zn plating: Experimental and molecular dynamics simulation

This paper combines experiments and molecular dynamics simulations to investigate the effects and mechanisms of different Mg and Si contents in hot-dip 55Al-Zn plating on the microstructure. Non-equilibrium molecular dynamics was used to simulate the diffusion process between plating and substrate. The structure and composition of the plated layers were analyzed by electron probe and transmission. Both experimental and simulation results show that Mg and Si elements tend to be enriched at the substrate interface and form the Mg2Si phase. The Fe-Al intermetallic compound layer can be divided into two parts, Fe4Al13(Si, Zn), which is far from the substrate, and Fe4Al13, which is close to the substrate, and grows along the direction perpendicular to the substrate interface. When the Mg content in the plating is 0, Si is enriched near the substrate and exists in the form of Si particles. When the Mg content in the plating is high, Si is present mainly in two forms: diffused in the Fe-Al intermetallic compound layer and formation of Mg2Si. The increase of Mg content in the plating promotes the breaking of Fe atomic bonds, but the aggregation of Mg elements hinders the diffusion of Fe. The Si dispersed in the intermetallic compound layer hinders the diffusion of Fe atoms and makes the intermetallic compound layer thinner. The above results explore the microscopic mechanism of the effect of Mg and Si elements on the plating layer at the atomic level and provide new ideas for the study of conventional hot-dip galvanized steel.

The influence of adatom diffusion on the formation of skyrmion lattice in sub-monolayer Fe on Ir(111)

Room temperature grown Fe monolayer (ML) on the Ir(111) single crystal substrate has attracted great research interests as nano-skyrmion lattice can form under proper growth conditions. The formation of the nanoscale skyrmion, however, appears to be greatly affected by the diffusion length of the Fe adatoms on the Ir(111) surface. We made this observation by employing spin-polarized scanning tunneling microscopy to study skyrmion formation upon systematically changing the impurity density on the substrate surface prior to Fe deposition. Since the substrate surface impurities serve as pinning centers for Fe adatoms, the eventual size and shape of the Fe islands exhibit a direct correlation with the impurity density, which in turn determines whether skyrmion can be formed. Our observation indicates that skyrmion only forms when the impurity density is below 0.006/nm2, i.e., 12 nm averaged spacing between the neighboring defects. We verify the significance of Fe diffusion length by growing Fe on clean Ir(111) substrate at low temperature of 30 K, where no skyrmion was observed to form. Our findings signify the importance of diffusion of Fe atoms on the Ir(111) substrate, which affects the size, shape and lattice perfection of the Fe islands and thus the formation of skyrmion lattice.

Transport property of topological crystalline insulator SnTe (100) and ferrimagnetic insulator heterostructures

• High quality SnTe/RE3Fe5O12 (RE=Eu, Y) epitaxial heterostructures were prepared. • Domain disorder is induced by Fe atom diffusion in SnTe through magnetic interface. • Two different magnetoelectrical transport in two heterostructures are observed. • Linear magnetoresistance and nonlinear Hall appear in SnTe/Eu 3 Fe 5 O 12 . Topological crystalline insulator (TCI) SnTe is a potential material for quantum electronic devices because of its attractive inherent sensitivity of band topology and highly mobile characteristic of Dirac fermions. The proximity effect at the interface of SnTe film can affect the topological surface transport and may result in novel quantum magneto-electric effects. Here, we study the magnetoelectrical transport properties of SnTe thin films grown on ferrimagnetic insulators Eu 3 Fe 5 O 12 (110) (EuIG (110)) and Y 3 Fe 5 O 12 (111) (YIG (111)) single-crystal underlayers by molecular beam epitaxy. Linear magnetic resistance (LMR) is observed in SnTe/EuIG heterostructures in the low field range, which is different from the weak antilocalization (WAL) characteristic of SnTe/YIG heterostructures. Especially, the double carrier characteristic with the coexistence of holes and electrons in SnTe/EuIG heterostructure is quite different from the holes as main carriers in SnTe/YIG, although the SnTe layer remains the same crystal plane (100) in the two heterostructures. The LMR in SnTe/EuIG is attributed to the topological surface Dirac electrons and disordered domain distribution in the SnTe layer which is in sharp contrast to the WAL of SnTe/YIG with ordered domain distribution in the SnTe layer. The present studies of transport properties not only provide a fundamental understanding of the transport mechanism of TCI and magnetite insulator heterostructure but also display the promising application probability for tunable topological electronic devices.

Quantitative x-ray diffraction analysis of strain and interdiffusion in β-Ga2O3 superlattices of μ-Fe2O3 and β-(AlxGa1−x)2O3

Superlattices composed of either monoclinic μ-Fe2O3 or β-(AlxGa1−x)2O3 with β-Ga2O3 spacers are grown on (010) β-Ga2O3 substrates using plasma-assisted molecular beam epitaxy. High-resolution x-ray diffraction data are quantitatively fit using commercial dynamical x-ray diffraction software (LEPTOS) to obtain layer thicknesses, strain, and compositions. The strain state of β-(AlxGa1−x)2O3 and μ-Fe2O3 superlattices as characterized using reciprocal space maps in the symmetric (020) and asymmetric (420) diffraction conditions indicates coherent growths that are strained to the (010) β-Ga2O3 lattice. β-(AlxGa1−x)2O3 and μ-Fe2O3 superlattices grown at hotter substrate temperatures result in crystal structures with better coherency and reduced defects compared to colder growths. The growth rate of μ-Fe2O3 is ∼2.6 nm/min at Tsub = 700 °C and drops to ∼1.6 nm/min at Tsub = 800 °C due to increased Fe interdiffusion at hotter substrate temperatures. Scanning transmission electron microscopy data of a μ-Fe2O3 superlattice grown at Tsub = 700 °C confirm that there is significant diffusion of Fe atoms into β-Ga2O3 layers.

Reaction Mechanism and Kinetic Model of Fe Thin Film Transformation into Monosulfides (FeS): First Step of the Fe Films Sulfuration Process into Pyrite

The sulfuration of metallic iron layers into pyrite (FeS2) is preceded by an initial stage characterized by the iron transformation into monosulfide, which acts as a precursor of the disulfide. This work presents a comprehensive reaction and kinetic model of the sulfuration reaction of metallic iron thin films into monosulfides when a molecular sulfur (S2) atmosphere is used. By slowing down the sulfuration reaction, we have been able to follow in situ the evolution of the transport properties (electrical resistivity and Seebeck coefficient) of the Fe films during their sulfuration reaction to monosulfides. We show that two different stages characterize this initial sulfuration: (1) the transformation of Fe into hexagonal pyrrhotite (Fe → Fe1–xSH) and (2) a partial crystallographic transformation of this hexagonal pyrrhotite into orthorhombic pyrrhotite (Fe1–xSH → Fe1–xSO). A two-step process can explain the pyrrhotite hexagonal phase formation, being first controlled by the surface adsorption of S2 on the external sample interface (S2/pyrrhotite) and second by the diffusion of Fe atoms through the formed pyrrhotite layer. By deducing the corresponding kinetic equations in terms of the experimental parameters (S2 partial pressure and thicknesses of the layers of present species), we can explain the evolution of the electrical resistance and Seebeck coefficient of the original Fe film during its transformation into monosulfide. At the same time, the appearance of the Kirkendall effect during the monosulfide phase formation is experimental and formally justified. The comprehensive description of this first stage of the complete sulfuration process of the Fe film into pyrite provides a layout to deeply discuss the influence of these intermedium phases on the final iron disulfide film characteristics and the appearance of potential film defects related to the experimental growth conditions.

Improvement in microstructure and mechanical properties of laser welded steel/aluminum alloy lap joints using high-entropy alloy interlayer

This study focused on the effect of a high-entropy alloy (HEA) interlayer on the improvement of microstructure and mechanical properties of steel/Al alloy lap joints by laser welding. The FeCoCrNiCu HEA improved metallurgical reaction by restricting the formation of Fe–Al intermetallic compounds (IMCs) at the interface. Results showed that in the steel on Al alloy lap joint without an interlayer, the discontinuous multi-phase IMCs layer mainly consisted of three types of IMCs, Fe-rich β-FeAl phases, and Al-rich θ-Fe4Al13 + η-Fe2Al5 phases. With the addition of a HEA interlayer, owing to the sluggish diffusion effect in the fusion zone (FZ), the diffusion of Fe atoms from FZ to the IMCs layer was significantly controlled, which limited the generation of IMCs at the FZ/Al alloy interface. The IMCs layer was only composed of single-phase β-FeAl with the absence of highly brittle Al-rich IMCs and the thickness of IMCs layer was reduced from 85 μm to 30 μm, resulting in the enhancement of toughness of the joint. Additionally, the improvement of mechanical properties of the joint, including microhardness and tensile shear strength was consistence with the reduction of brittleness of IMCs at the interface.

Diffusion behavior of iron and samarium atoms in Sm2Fe17 alloy compound layer

The Sm2Fe17 alloy compound has been widely studied and used as a precursor for Sm2Fe17Nx rare-earth permanent magnets. However, the growth mechanism of Sm2Fe17 remains unclear. In this study, based on the high temperature diffusion method, a Sm2Fe17 layer was prepared by fabricating a Sm–Fe (sat)/Fe(s) diffusion couple in the temperature range of 1060–1140 °C. Results indicated that the diffusion of Fe and Sm atoms is the rate-determining step in the growth of the Sm2Fe17 layer. The atomic concentrations of Fe and Sm in samples with different holding times at 1060–1140 °C were analyzed using an electron microprobe, which revealed that the growth of the Sm2Fe17 layer primarily depended on the diffusion of Fe atoms. The diffusion coefficients of Fe atoms in the Sm2Fe17 layer were 2.33 × 10−9, 4.29 × 10−9, and 5.37 × 10−9 cm2 s−1 at 1060, 1100, and 1140 °C, respectively. Moreover, the relationship between the diffusion coefficient of Fe atoms (DFe) and temperature (T) was obtained.

Microstructures and mechanical properties of YG18 cemented carbide/40Cr steel joints vacuum brazed using Ag–Cu–Ti filler metal

YG18 cemented carbide and 40Cr steel were brazed using Ag–Cu–Ti filler metal under vacuum, and the microstructural evolution of the YG18/Ag–Cu–Ti filler metal/40Cr steel brazed-joint interface was investigated to determine how brazing temperature affected the brazed-joint microstructure, bonding strength, and fracture behavior. At the YG18 cemented carbide/filler metal interface, Ti atoms in the filler metal and C atoms in the YG18 cemented carbide formed a continuous TiC layer, reducing the difference in thermal expansion coefficients between the YG18 cemented carbide and filler metal. At the 40Cr steel/filler metal interface, Ti atoms in the filler metal and C atoms in the 40Cr steel formed a continuous TiC layer, preventing the diffusion of Fe atoms to the cemented carbide side and formation of a hard, brittle phase. YG18 cemented carbide/TiC/Cu2Ti/Ag–Cu eutectic + TiCu granules/TiC/40Cr steel-brazed joints were obtained. With increasing brazing temperature from 860 to 920 °C, the bonding strength of the YG18 cemented carbide/40Cr steel joint initially increased and then decreased. The joint brazed at 900 °C for 10 min failed in the middle of the brazing seam, and its average bonding strength was 235 MPa.

In situ thermal annealing transmission electron microscopy of irradiation induced Fe nanoparticle precipitation in Fe–Si alloy

The typical experimental conditions inside a transmission electron microscope (TEM), such as ultra-high vacuum, high-energy electron irradiation, and surface effects of ultrathin TEM specimens, can be the origin of unexpected microstructural changes compared with that of bulk material during in situ thermal-annealing experiments. In this paper, we report on the microstructural changes of a Fe–15%Si alloy during in situ TEM annealing, where, in its bulk form, it exhibits an ordering transformation from D03 to B2 at 650 °C. Using a heating-pot type double tilt holder with a proportional–integral–differential control system, we observed the precipitation of α-Fe both at the sample surface and inside the sample. Surface precipitates formed via surface diffusion are markedly large, several tens of nm, whereas precipitates inside the specimen, which are surrounded by Fe-poor regions, reach a maximum size of 20 nm. This unexpected microstructural evolution could be attributed to vacancies on Si sites, which are induced due to high-energy electron irradiation before heating, as well as enhanced thermal diffusion of Fe atoms.

Effect of external magnetic field on resistance spot welding of aluminium to steel

Resistance spot welding of aluminium to steel with magnetic-assisted apparatus was performed for the first time to understand the metallurgical joining mechanism in the melt region and at the material interface. The electromagnetic force promoted circular motion of the molten metal and accelerated the diffusion of Fe atoms to the aluminium sheet, which induced finer grains, thinner intermetallic compound layers, reduced interface defects, and elevated hardness of the resulting aluminium nugget. Coach peel tests revealed that welds made with an external magnetic field presented enhanced strength and ductility compared to welds made with no external magnetic field. The enhanced strength and ductility resulted in a transition of the fracture behaviour from brittle interfacial mode to ductile button pullout mode, and increased the peak load and the energy absorption by 90% and 1327%, respectively.

Wear properties of self-lubricating Cr x S y /Ni coatings on 304 stainless steel by pre-placed laser cladding

ABSTRACT Self-lubricating NiCrBSi–Ni/MoS2 coatings are prepared on 304 stainless steel by pre-placed laser cladding, in which Ni/MoS2 is almost completely decomposed and the Cr x S y anti-friction phase is in situ generated. Meanwhile, (Cr, Fe)2B and (Cr, Fe)7C3 are generated from the molten pool as a result of oversaturated B and C atoms in γ-Ni and the diffusion of Fe atoms. Therefore, the composite coatings are mainly composed of γ-(Ni, Fe), (Cr, Fe)2B, (Cr, Fe)7C3, and Cr x S y . When compared with the substrate, the wear rate of the coatings with 20 wt-% Ni/MoS2 is reduced by 21.16%, owing to the Cr x S y lubricating phase, while it is reduced by 25.61% for the coatings with 5 wt-% Ni/MoS2, owing to blocky (Cr, Fe)2B or (Cr, Fe)7C3 hard phases. The wear mechanism of the coatings is adhesive wear and oxidative wear.

High-pressure preparation of high-hardness CoCrFeNiMo0.4 high-entropy alloy

The CoCrFeNiMo0.4 high-entropy alloys (HEAs) were synthesized by a high-pressure solid-state reaction at 3–5 GPa and held for 3–10 min at 1200 °C. The microstructure and mechanical properties of the sample were influenced by the pressure and holding time, which was confirmed when the Co, Cr, Fe, Ni, and Mo atoms diffused to form HEAs. The increased pressure hindered the diffusion between atoms and thus inhibited the formation of HEAs. Under the influence of the enthalpy of mixing between elements, Fe had the strongest repulsive force on the system and the weakest diffusion effect, but increasing the holding time promoted the diffusion of Fe atoms. Compared with the microhardness reported in other studies, the maximum hardness in our work was 449.1 HV, which represents a maximum increase of approximately 80%. The synergistic effects of the solid-solution strengthening of the system and the serious lattice distortion effect caused by large Mo atoms and high pressure were the dominant mechanisms responsible for the enhanced microhardness of the sintered HEAs under extreme conditions.

The investigation on the fabrication and microstructure of a novel core-shell structure reinforced iron matrix composite

To make the steel/iron composites with better comprehensive mechanical properties, a novel iron matrix composite reinforced with three-dimensional core-shell structure (CS) reinforcing particulates is designed and fabricated via powder hot-pressing sintering process. Studies have shown that the CS consists of isolated soft W core and dense hard shell, that is, showing the structural characteristics of “inner soft and outer hard”. When the carbon content of the raw material powder Fe–W–C ternary system is 0, 0.5, 1.0, 1.5 and 2.0 wt%, the CS of W@(Fe7W6 + Fe2W), W@Fe3W3C, W@(W2C + WC + Fe3W3C)Ⅰ, W@(W2C + WC + Fe3W3C)Ⅱ, and W@(W2C + WC + Fe3W3C)Ⅲ is formed in the matrix, respectively. The formation of CSs with different characteristics is mainly due to the diffusion of Fe atoms and/or C atoms into the W lattice to undergo a diffusion-type solid state phase transformation to form corresponding compounds and the formation kinetics of different phases determined by different carbon concentrations. Furthermore, the results of nanoindentation and Vickers indentation show that the hardness of the shell layer is much greater than that of the metal W core and matrix, but its plastic deformation rate is much smaller than that of the metal W core and matrix. The metal W core and the iron matrix can significantly inhibit the length of the crack propagation, thereby improving the toughness of the composite. And the hard shell layer with high volume fraction can significantly improve the strength of the composite. Therefore, the iron matrix composite reinforced with three-dimensional CS reinforcing particulates is expected to obtain good toughness and excellent strength, and this work may provide a new strategy for the structural design of steel/iron materials.