Interdiffusion Of Elements Research Articles

An innovative interlayer improving the interfacial connection of FeCoNiCrTi coating on copper surface

To improve the performance of copper surface, a FeCoNiCrTi high entropy alloy coating was first attempted to be prepared on copper substrate by plasma cladding. The obtained single-layer coating had a smooth and flat surface, but the interfacial connection was poor. Interfacial defect analysis results showed that the alloying elements dominated by Ti in the coating reacted with the CuO formed during the preheating process on copper surface. A large amount of TiO2 and other complex oxides were generated and distributed at the interface, which hindered the interfacial connection. After introducing a Ni60A interlayer, the interface reaction between FeCoNiCrTi alloy and copper oxide was avoided, and the inter-diffusion of elements was promoted, thus forming a good metallurgical bonding. Furthermore, due to the dilution effect of Ni60A interlayer, the performance of FeCoNiCrTi surface layer slightly decreased, but still far superior to the Ni60A coating. The microhardness of FeCoNiCrTi surface layer was about 10.7 times that of copper substrate. The wear loss of the developed coating is only 1/2 of that of the single Ni60A coating at 600 °C. This study has a great significance for extending the application of FeCoNiCrTi high entropy alloy coatings in surface strengthening on copper.

Effect of bell annealing on the interface microstructure and mechanical properties of titanium/steel composite plates prepared by hot rolling

This study investigates the effect of bell annealing (600°C-750°C/3 h-15 h) on the interfacial microstructure and mechanical characteristics of hot-rolled titanium/steel (Ti/steel) bi-metallic plates, aiming to improve their mechanical performance and deformation compatibility. The interfacial bonding mechanism and growth process of the interfacial TiC layer were studied using multi-scale characterization. The microstructural evolution during annealing and the effect of the TiC layer on element interdiffusion were considered. Results show that the TiC interlayer inhibits Ti and Fe diffusion, preventing undesirable Ti-Fe phases, and the TiC layer thickens towards the Ti side. Higher annealing temperatures and longer times worsened the grain size difference between the Ti and steel layers and produced a thick TiC layer, severely degrading deformation compatibility. Microcracks, caused by severe lattice mismatch, are mostly initial at the α-Fe/TiC interface during plastic deformation. Thin to moderate TiC layers resulted in a combination of ductile and brittle fractures, while thick layers led to brittle fractures. In terms of mechanical properties, the ultimate tensile strength (UTS), yield strength (YS), shear strength, and elongation (EL) of the hot-rolled composite plate were measured at 337 MPa, 232 MPa, 238 MPa, and 29%, respectively. All annealed samples exhibited a reduction in UTS, YS, and shear strength compared to the hot-rolled state; however, they demonstrated improved elongation and deformation compatibility, with the elongation achieving its optimal value at 650°C-3 h. The annealing, at 650°C for 3 h, was identified as the optimal condition for post-rolling heat treatment, resulting in a composite plate with a comprehensive mechanical performance characterized by UTS, YS, shear strength, and EL values of 267 MPa, 127 MPa, 171 MPa, and 46%, respectively.

Preparation and interdiffusion behaviour of a NiCrAlY coating with high entropy ceramic diffusion barrier

In order to solve the problem of elemental interdiffusion between the superalloy and coating, the diffusion barrier of (AlCoCrNiRe) and (AlCoCrNiRe)O between the N5 superalloy and NiCrAlY coating was prepared by magnetron sputtering. Isothermal oxidation behaviour of the NiCrAlY coatings with diffusion barrier was evaluated at 1050 °C. The results show that the application of (AlCoCrNiRe) and (AlCoCrNiRe)O diffusion barriers significantly reduced the precipitation of TCP phase in the substrate. (AlCoCrNiRe)O high entropy ceramic diffusion barrier has a better effect of inhibiting interdiffusion because of its own properties and the oxides formed in situ. Furthermore, the NiCrAlY coating with (AlCoCrNiRe)O high entropy ceramic diffusion barrier provides higher resistance to high-temperature oxidation for the substrate.

Interdiffusion mechanism between EB-PVD deposited CoCrAlY bond-coat and superalloy substrate under high-temperature oxidation service conditions in gas turbine

The interdiffusion mechanism between EB-PVD deposited CoCrAlY coating and superalloy substrate under high-temperature oxidation atmosphere in actual gas turbines was investigated both experimentally and through thermodynamics and kinetics simulation. The interdiffusion behavior differs at different regions of blade due to the different service temperatures. The elemental interdiffusion and phase transformation behavior were investigated and discussed. Needle-like topologically close-packed phase and σ-CrCoNi phase have precipitated within the secondary reaction zone due to the γ→γ’ transition and the uphill diffusion of Cr, W, and Mo. Decreasing the Co content in the MCrAlY bond-coat can inhibit the interdiffusion behavior to a certain extent.

Phase-Field Modeling of Kinetics of Diffusive Phase Transformation in Compositionally-Graded Ni-Based Superalloys

AbstractKinetics of the $$\gamma$$ γ /$$\gamma ^{\prime}$$ γ ′ phase transformation and the interdiffusion phenomena in single-crystal Ni-based superalloys, under isothermal annealing and composition gradient, is investigated through the phase-field and continuum diffusion models. The employed models in the present work exploit CALPHAD-based thermodynamics and kinetics databases, in order to perform realistic simulations. We specifically predict the interdiffusion of elements for a hypothetical alloy AlCoCrTaNi/Ni diffusion couple, equivalent to the CMSX-10/Ni diffusion couple, at 1323 K. Accordingly, the phase fraction and morphology of $$\gamma ^{\prime}$$ γ ′ precipitations in the $$\gamma$$ γ matrix is simulated as well. The implemented multi-component diffusion model takes into account vacancies and pore formation, reflecting Kirkendall effect. Furthermore, the time evolution of morphology parameters of the precipitate-depleted zone in the diffusive region (i.e., the position and the size) are estimated.

Interfacial inhomogeneous plastic deformation during rotary friction welding of dissimilar AA2219-SS321 joint combination with AA6061 interlayer

This research investigates the inherent radial non-uniformity within the rotary friction welding process, particularly concerning microstructure attributes like grain size, grain boundaries, misorientation angles, and interlayer presence along the radial axis. SS321-AA2219 rotary friction welding was carried out with and without an AA6061 interlayer. The numerical thermal model suggests increase in temperatures from the center to the periphery, due to non-uniform heat generation. Also, dissimilar material across the interface resulted in an asymmetric temperature profile along axial direction. Plastic deformation on the Aluminum side suggests dynamic recrystallization and grain refinement, whereas pronounced low-angle grain boundary (LAGB) formation near the SS side interface validates dynamic recovery. A radial non-uniformity in microstructure is observed, with metrics such as average grain size, LAGB fraction, and misorientation showing an increase from the center towards the periphery. The insertion of an interlayer alters process dynamics, manifesting in reduced temperatures and heightened forces, resulting in a more consolidated joint by enhancing the strength by 31 %. Interdiffusion of elements across the interface formed Fe-Al intermetallic compounds (IMC) confirmed with X ray diffraction. Fractography analysis elucidates the presence of rubbing marks and facet surfaces in interlayer-less joints, while joints with interlayer display sticking and dimples.

High dislocation-density silver particle interlayer for high-quality YSZ and Al2O3 joints

An Ag particle interlayer was adopted to join YSZ to Al2O3 ceramics in air directly. In comparison with the traditional Ag-CuO braze used in our previous work, the Ag particle interlayer prevented the formation of the brittle compound (CuAl2O4) layer along the ceramic interface. Sintering effect of particulate Ag and high-density dislocations in the interlayer are the major contributors to recrystallization of Ag and elemental interdiffusion. High Resolution Transmission Electron Microscope images confirmed that atomic bonding was achieved between the interlayer and Al2O3. Joining parameters, including temperatures and pressures, were optimized, resulting in the maximum shear strength of the joint (∼80 MPa) obtained at 950 °C/30 min with the external pressure of 0.9 MPa, which is 78 % higher than that of the joint brazed by Ag-CuO.

The effect of post-annealing on the performance of the Cu2ZnSnS4 solar cells

Cu2ZnSnS4 (CZTS) solar cells commonly undergo post-annealing treatments to enhance their performance. However, multiple concurrent effects, including Cu–Zn disorder, Na diffusion from the back contact, CZTS grain boundary passivation, and elemental interdiffusion at the CdS/CZTS interface, can occur simultaneously during post-annealing, making it challenging to isolate their specific influence on device performance. To address this complexity, we have utilized Cu–Zn-disordered CZTS absorbers to eliminate the influence of Cu–Zn disorder in this study. Post-annealing experiments conducted at 120 to 300 °C in nitrogen and air atmospheres aim to decouple and assess the impact of different annealing conditions on the performance of CZTS solar cells. Our findings suggest that the optimal post-annealing might be a combined effect of two distinct processes: CZTS absorber surface passivation occurring at 325 °C and CdS crystallization at 225 °C. Hence, improvement in device performance could result from multiple concurrent mechanisms occurring at different temperatures.

Liberalizing the effects of Al and Cr in coatings for enhanced interface stability with Mo-rich Ni3Al-based superalloys

The interfacial behaviors between protective coatings and substrate single-crystal superalloys significantly impact their service performances. This work focuses on the elements interdiffusion and microstructural evolution at the interface between a NiCrAlY coating and a series of high-Mo Ni3Al-based single-crystal superalloys, through the coupled phase-field simulations and DICTRA kinetics calculations of their model systems. The critical roles of Al and Cr played in the microstructural evolution at coating/superalloy interface have been confirmed, which requires the appropriate content decreases of Al and Cr in the coating at 1100 °C. However, the addition of Mo reduces the driving force of element diffusion from coating to substrate by increasing the activities of Al and Cr in superalloy. Moreover, increasing the Mo content in superalloy from 8 wt% to 10 wt% could also counteract the promoting effect of Al on Ni mobility and mitigate the γ′ coarsening and detrimental TCP precipitation. Therefore, the effects of Mo enable the reasonable increase of Al content in coating to better balance the interfacial stability and oxidation resistance of coated superalloy, besides its advantage in reducing the anisotropy of TCP precipitate. The obtained interfacial evolution mechanisms resulting from the phase transformation thermodynamics and element interdiffusion kinetics are expected to aid the coating design for advanced single-crystal superalloys servicing at ultra-high temperature.

High-Valence Ion Doped Compositionally Partitioned Li[Ni0.78Co0.10Mn0.12]O2 Cathode for Advanced Lithium-Ion Batteries

Numerous approaches have been employed to reduce the intrinsic instability of Ni-rich cathodes. Among them, the introduction of concentration gradient (CG), i.e., a strategy to protect the labile Ni-enriched compartment with a chemically protective Mn-rich shell, has proven successful in commercial applications.1 However, because the segmentation of transition metal (TM) constituents and the formation of unique geometric configurations are characteristics inherited from the CG hydroxide precursor; it is crucial to select the optimal calcination temperature and precisely control it.2 Excessive thermal energy input can result in concentration planarization because the CG of the hydroxide precursor is intrinsically susceptible to the interdiffusion of TM elements during lithiation. Moreover, the immoderate coarsening of the primary particles can eliminate the advantageous features of the CG design by producing equiaxed primary particles.2 In this study, we propose a strategy that can effectively ameliorate the deterioration of Ni-rich CG cathodes resulting from excessive thermal energy input and remarkably improve their electrochemical cycling performance. It was revealed that a trace amount of tungsten incorporation during the cathode calcination can effectively mitigate the high-temperature-induced cathode degeneration and maintain outstanding product quality over a wide range of temperatures. Thus, the proposed strategy opens new avenues for the facile synthesis of long-life Ni-rich CG cathodes. Reference s : [1] Y.-K. Sun, S.-T. Myung, B.-C. Park, J. Prakash, I. Belharouak, K. Amine, Nat. Mater. 8 (2009) 320-324.[2] G.-T. Park, H.-H. Ryu, T.-C. Noh, G.-C. Kang, Y.-K. Sun, Mater. Today 52 (2022) 9-18.

Effect of micron/nano Nb particles on high-temperature oxidation behavior of TiAl alloy/thermal barrier coating system

In this study, the effect of NiCoCrAlY bond coating modified by micron- and nano-sized Nb particles on the oxidation behavior of a TiAl alloy/thermal barrier coating (TBC) system was investigated. The results show that the addition of micron-sized Nb particles slightly decreased the oxidation resistance of the TNM/TBC system, while the addition of nano-sized Nb particles significantly increased the oxidation resistance. The growth stress from the oxidation of micron-sized Nb particles and the Kirkendall effect lead to localized thickening (tumor effect) of the thermally grown oxide (TGO). Severe internal oxidation occurs in the bond coating modified by micron-sized Nb particles, greatly reducing the mechanical properties and antioxidant properties of the TNM/TBC system. However, these micron-sized Nb particles are deposited at the bond coating/TiAl matrix interface, acting as an in-situ diffusion barrier and partially hindering element interdiffusion. Conversely, nano-sized Nb particles induce the formation of fine columnar crystals in the TGO and promote the external diffusion of Al elements, thereby maintaining a low growth rate and excellent continuity of the TGO. Additionally, the Nb element dissolves into the matrix phase, and the formation of nano Nb-Al₂O₃ core-shell structures effectively improves the deformation resistance and failure resistance of the bond coating.

Strengthening Ti3SiC2/Cu brazed joint assisted with cold spray additive manufacturing: Lower brazing temperature through interdiffusion and graded reinforcement for stress relaxation

Graded composite fillers exhibit unique advantages in alleviating residual stress in ceramic/metal brazed joints. However, traditional methods for preparing graded composite fillers are often complex and may deplete their strengthening phases. In this study, cold spray additive manufacturing was employed to fabricate yttria-stabilized zirconia (YSZ)-Ti25Zr25Ni25Cu25-Ag graded composite coatings on Cu substrates to serve as fillers. The graded composite coatings and the resultant Ti3SiC2/Cu brazed joints were systematically characterized to elucidate the deposition mechanism of the coatings and its residual stress-relaxed mechanism. The bondings between particles in the coatings, based on their plastic deformation ability, were classified into noncrystalline weak bonds and homogeneous strong bonds. Both bondings facilitated the elemental interdiffusion between filler and Cu substrate during the heating process, which contributed to the formation of Ag-Cu eutectic. This significantly reduced the required brazing temperature and its induced residual stress. Furthermore, the solid phase transformation of graded-distributed YSZ within the brazing seam from tetragonal to monoclinic achieved a smooth thermal transition and releasing residual stress at the same time. Consequently, the shear strength of the brazed joint reached to the highest value of 110.23 ± 3.45 MPa, which was Much higher than the previously reported values. This study introduces a novel method for residual stress relaxation assisted with cold spray technology and broadens its application in the brazing field.

Formation mechanism of TiC twin during densification of SiCf/Ti2AlNb composites

SiCf/Ti2AlNb composites were fabricated using the magnetron sputtering precursor wires method in conjunction with the hot isostatic pressing (HIP) technique. The morphology, elemental distribution, and structural characteristics of the interfacial reaction layer (RL) were examined through scanning electron microscopy (SEM), transmission electron microscopy (TEM), and wavelength dispersive spectroscopy (WDS). The results showed that the interface between SiC fibers and Ti2AlNb reacted to form TiC and α2. Due to the interdiffusion of elements at the interface, a small amount of Al atoms existed in the TiC layer. These Al atoms reduced the stacking fault energy (SFE) of TiC, which is beneficial for the formation and stability of Σ3{111} twin boundaries.

Interdiffusion behavior and compositional tailoring of AlCoCrFeNiY high-entropy alloy coating on a Hastelloy-X superalloy

This study investigated the microstructural evolution and interdiffusion behavior of an AlCoCrFeNiY coating deposited on a Hastelloy-X superalloy substrate at 1050 °C, 1100 °C and 1150 °C, and compared it with a conventional NiCoCrAlY coating. Element interdiffusion behavior indicates that Al and Co diffuse inward from the coating to the substrate, while Ni and Cr diffuses outward from the substrate to the coating. However, the interdiffusion behavior of Fe is different in two types of coating/substrate systems, which results from the big difference in Fe concentration. The AlCoCrFeNiY coating undergoes extensive β to γ phase transformation than the NiCoCrAlY coating, and thermodynamic calculations suggest that Fe can dramatically extend the γ/σ two-phase region. This causes formation of a thicker β-depleted zone near the coating/substrate interface and more Cr-rich σ phase precipitates in the AlCoCrFeNiY/Hastelloy-X system. Based on thermodynamic calculations of the effect of Fe content on Y solubility and phase composition, as well as the chemical potential difference in Fe, a novel Ni23Co17Cr12Al10FeY coating is proposed to reduce element interdiffusion without sacrificing oxidation resistance.

Interdiffusion mechanism of hybrid interfacial layers for enhanced electrical resistivity and ultralow loss in Fe-based nanocrystalline soft magnetic composites

Soft magnetic composites (SMCs) composed of ferromagnetic particles and insulating binder are highly desired in energy-saving and high-efficiency devices for their high electrical resistivity and softer saturation characteristics. However, traditional insulation coatings are facing thermal instability, inhomogeneous distribution, and magnetic dilution, presenting a major challenge for the trade-off relationship between power loss and permeability. Here, the phosphate-coated FeSiBCuNb/SiO2 SMC is successfully fabricated by a unique interdiffusion effect in hybrid interfacial layers, which shows a combination of ultralow power loss of 135.8 kW/m3 (50 kHz/100 mT), high effective permeability of 80.6, and good temperature stability. The interdiffusion behavior between Si/O and Fe/P/O elements promotes the formation of ultrathin, uniform, and multilayer interface structure, which alleviates the magnetic dilution. Penetrating oxidation at the edge interface and elements interdiffusion effect contribute to a higher electrical resistivity induced by hot isostatic pressing with rapid quenching, leading to a low eddy current loss. Synergistic effect of isostatic pressures and rapid quenching facilitates the formation of high-density Cu clusters corresponding to ultrafine microstructure, which is beneficial for low coercivity and low hysteresis loss. This study involves the interdiffusion mechanism of hybrid interfacial layers and nanocrystalline behavior, providing a new strategy for the next-generation of high-performance SMCs.

The origin of magnetic ordering and reduced mobility in KTaO3-based 2DEGs: Interfacial interdiffusion

Recently, KTaO3 (KTO)-based 5d two-dimensional electron gases (2DEGs), characterized by robust spin–orbit coupling, have emerged as promising candidates for future spintronic devices. However, the carrier mobility of KTO-based 2DEGs is typically lower than that of SrTiO3-based 2DEGs, which limits their further development. It is imperative to explore the underlying causes of diminished carrier mobility and devise strategies to augment it. In addition, the genesis of magnetism within KTO-based 2DEGs remains ambiguous. In this study, the 2DEG within the amorphous-EuTiO3/KTO (a-ETO/KTO) heterostructure demonstrates a high electron mobility of 289.1 cm2 V−1 s−1, which exhibits a significant decrease as the film growth temperatures increase. This decrease can be primarily ascribed to electron scattering by impurities, which is induced by the amplified interfacial element interdiffusion at a higher film growth temperature. In addition, the magnetism of 2DEGs for samples grown at different temperatures shows an increasing trend with growth temperatures, which is predominantly derived from the interdiffusion of Eu atoms. This study provides an in-depth analysis of the origin of magnetic ordering and reduced mobility in KTO-based 2DEGs, which will promote the further development of 2DEGs for future applications in electronic devices.

Parameters Optimization for Electrophoretic Deposition of Mn1.5Co1.5O4 on Ferritic Stainless Steel Based on Multi-Physical Simulation

Solid oxide fuel cells (SOFCs) are an effective and sustainable energy conversion technology. As operating temperatures decrease, metal interconnects and supports are widely employed in SOFCs. It is critical to apply a protective coat on ferritic stainless steel (FSS) to suppress Cr evaporation and element interdiffusion under high temperatures. Electrophoretic deposition (EPD) is a promising approach for depositing metal oxides on FSS substrate. Here, a method based on 3D multi-physical simulation and orthogonal experimental design was proposed to optimize deposition parameters, including applied voltage, deposition time, and electrode distance. The EPD process to deposit Mn1.5Co1.5O4 particles in a suspension of ethanol and isopropanol was simulated and the effects of these three factors on the film thickness and uniformity were analyzed. The results indicate that applied voltage has the greatest impact on deposition thickness, followed by deposition time and electrode distance. Meanwhile, deposition time exhibits a more significant effect on film unevenness than applied voltage. Additionally, the particle-fluid coupling phenomenon was analyzed during the EPD process. In practice, these deposition parameters must be selected appropriately and the deposition time must be controlled to obtain a uniform coating. The proposed method can reduce cost and shorten the design period.

Tuning Li/Ni mixing by reactive coating to boost the stability of cobalt-free Ni-rich cathode

Cobalt-free cathode materials are attractive for their high capacity and low cost, yet they still encounter issues with structural and surface instability. AlPO4, in particular, has garnered attention as an effective stabilizer for bulk and surface. However, the impact of interfacial reactions and elemental interdiffusion between AlPO4 and LiNi0.95Mn0.05O2 upon sintering on the bulk and surface remains elusive. In this study, we demonstrate that during the heat treatment process, AlPO4 decomposes, resulting in Al doping into the bulk of the cathode through elemental interdiffusion. Simultaneously, PO43− reacts with the surface Li of material to form a Li3PO4 coating, inducing lithium deficiency, thereby increasing Li/Ni mixing. The suitable Li/Ni mixing, previously overlooked in AlPO4 modification, plays a pivotal role in stabilizing the bulk and surface, exceeding the synergy of Al doping and Li3PO4 coating. The presence of Ni2+ ions in the lithium layers contributes to the stabilization of the delithiated structure via a structural pillar effect. Moreover, suitable Li/Ni mixing can stabilize the lattice oxygen and electrode-electrolyte interface by increasing oxygen removal energy and reducing the overlap between the Ni3+/4+eg and O2− 2p orbitals. These findings offer new perspectives for the design of stable cobalt-free cathode materials.

Evaluation of shear bond strength based on substructure materials and ceramic veneering techniques.

Bilayered restorations have both the strength of the substructure material and the esthetics of the veneer material; however, they should have appropriate bonding between the two materials. This study aimed to evaluate the shear bond strength (SBS) according to the substructure material and veneering technique used in bilayered restorations. The experimental group was divided into four groups (n = 15 per group) based on the substructure materials (cobalt-chromium [Co-Cr] alloy and 3 mol% yttrium-stabilized tetragonal zirconia polycrystal [3Y-TZP]) and veneering techniques (pressing and layering). Veneering was performed with disk shape (diameter: 5mm, height: 2mm) on a substructure using each veneering technique. Shear stress was applied to the interface of the substructure and the veneering ceramic using a universal testing machine. The shear bond strength, according to the substructure and veneering technique, was analyzed using a two-way analysis of variance with a post-hoc Tukey's honestly significant difference test. The failure mode was observed, and the surface was analyzed using a scanning electron microscope and energy-dispersive spectroscopy. The shSBS of the Co-Cr alloy and 3Y-TZP substructure was not different (p > 0.05); however, the pressing technique showed a higher SBS than the layering technique (p < 0.05). The SBS did not differ depending on the veneering technique in the Co-Cr alloys (p > 0.05), whereas the SBS in the pressing technique was higher than that in the layering technique for 3Y-TZP (p < 0.05). In the layering technique, the Co-Cr alloy showed a higher SBS than 3Y-TZP (p < 0.05). In the failure mode, mixed failure occurred most frequently in all groups. Extensive elemental interdiffusion was observed through the opaque layer in the Co-Cr alloy, regardless of the veneering technique. In 3Y-TZP, a wider range of elemental interdiffusion was observed in the pressing technique than in the layering technique. In bilayered restorations with a 3Y-TZP substructure, the pressing technique yielded higher bonding strength than layering. Using the layering technique, 3Y-TZP showed a lower SBS than the Co-Cr alloy. In bilayered restorations using 3Y-TZP as a substructure, the veneering technique and thermal compatibility of the materials must be considered.

Altered spinels act as a mirror of multi-episodic fluid metasomatism in the forearc mantle: An example from the Minhe ophiolite in Qilian Orogen, NW China

Forearc mantle peridotites commonly undergo complex melt/fluid metasomatism, which inevitably has a considerable influence on their geochemical compositions at the whole-rock scale. Serpentinites predominantly comprise the Minhe ophiolite, which is a fragment of the Proto-Tethys Ocean that outcrops in the Qilian Orogen in NW China. These serpentinites contain zoned spinels that vary compositionally from the centers to the margins, with a spinel core overgrown by ferritchromite layer and magnetite at the outermost rim. The mineral chemistry of the spinel cores (i.e., Cr#, Mg#, Cr2O3, and Al2O3) suggests that the protolith of the serpentinites was an oceanic mantle remnant in a forearc setting. Moreover, the ferritchromite exhibited increases in Fe, Mn, Sc, and Ni contents and decreases in Mg, Cr, Al, V, Zn, and Ga contents. Considering the linear correlation among elements (e.g., Co, Ni, and Zn) and the absence of mineral inclusions, the ferritchromite likely formed through ionic substitutions induced by slab fluids. The magnetite was enriched in Cr, Ni, V, Zn, Co, and Cu, but did not have a magmatic origin owing to low V concentrations. All evidence indicates that the peridotites underwent at least two episodes of fluidic metasomatism in the subduction zone. During early slab subduction, aqueous fluids released from the dehydration of the subducted slab directly serpentinized the forearc mantle peridotites, thereby altering the olivine and orthopyroxene to lizardite/chrysotile. During this process, certain mobile elements (e.g., Fe, Ni, and Mn) in the fluids and/or olivine serpentinization were incorporated into existing spinels, favoring ferritchromite growth. The second fluidic episode was dependent on prograde metamorphism at greater depths in the subduction channel, which not only produced antigorite via the recrystallization of lizardite and chrysotile, but also drove the fluids towards a more oxidizing state, thereby facilitating the growth of Cr-magnetites. Subsolidus re-equilibration controlled by fluid infiltration further promoted the inter-diffusion of elements (e.g., Cr, V, Co, Ni, Cu, and Zn) in the zoned spinels.