Key Takeaways & Executive Findings
- •• • The STL6/TiN composite coating achieved a corrosion current density of 0.37 μA/cm², a reduction of at least one order of magnitude compared to the uncoated F347 substrate, directly translating to a lower corrosion rate and extended component lifespan in chloride-rich environments. • • The passivation potential of the composite coating reached 939 mV, the highest among all tested samples, indicating a more stable and protective passive film that delays breakdown and pitting initiation under anodic polarization. • • The impedance modulus |Z| of the STL6/TiN coating was the largest, confirming superior barrier properties and charge-transfer resistance, which are critical for maintaining structural integrity in marine or chemical processing applications. • • Microstructural analysis revealed a defect-free, metallurgically bonded interface with elemental diffusion, and the STL6 layer contained minimal oxides; this ensures strong adhesion and prevents coating spallation, a common failure mode in thermally sprayed coatings.
China Advanced Materials & Deep-Tech Radar
Get verified English translations, SEM micrographs & open-access PDF alerts from China's leading state key laboratories delivered to your inbox every Monday at 08:00 EST.
Abstract
The corrosion resistance of ASTM A182 F347 austenitic stainless steel was enhanced via a two-stage surface engineering protocol: plasma transferred arc deposition of Stellite 6 (STL6) followed by chemical vapor deposition of titanium nitride (TiN). Microstructural characterization confirmed a metallurgically bonded interface with elemental interdiffusion; the STL6 layer exhibited a graded structure from planar/equiaxed grains at the substrate to columnar dendrites and fine equiaxed grains at the surface, with minimal oxide content. Electrochemical testing in 3.5% NaCl solution revealed that the STL6/TiN composite coating reduced the corrosion current density to 0.37 μA/cm², the lowest among the three sample types (F347 substrate, F347-STL6, and F347-STL6-TiN). The composite coating also demonstrated the highest passivation potential (939 mV) and the largest impedance modulus |Z|, indicating superior passive film stability. Post-corrosion analysis showed that the F347 substrate suffered extensive deep pitting, while the STL6 coating exhibited intergranular corrosion with an oxide film. In contrast, the STL6/TiN composite coating displayed only sparse shallow pits. The improved performance is attributed to the formation of a dense Cr₂O₃ passive film on the STL6 layer and the additional barrier provided by the TiN topcoat. These findings offer a viable route for extending the service life of F347 stainless steel in aggressive environments.
1. Introduction
F347 stainless steel is widely used in nuclear and chemical industries due to its resistance to intergranular corrosion, but it remains susceptible to pitting and crevice corrosion in chloride-bearing environments. Conventional surface treatments such as single-layer plasma welding or thin-film coatings often fail to provide adequate long-term protection because they either lack sufficient thickness or suffer from poor adhesion, leading to premature failure. The need for a robust, multi-layered coating that combines a thick, metallurgically bonded underlayer with a dense, chemically inert topcoat has become evident.
This study addresses the bottleneck by sequentially applying Stellite 6 via plasma transferred arc welding and TiN via chemical vapor deposition. The STL6 layer provides a corrosion-resistant base with a graded microstructure that mitigates stress and promotes elemental diffusion, while the TiN topcoat acts as an additional barrier against aggressive ions. Electrochemical and microstructural analyses demonstrate that this composite architecture significantly outperforms both the bare substrate and the single-layer STL6 coating, offering a practical solution for enhancing the durability of F347 components in harsh service conditions.
Loading authentic research manuscript (Pages 1–5)...
YU Huaming, GU Jinlong, WU Xiaokang, ZHU Gangxian, ZHANG Xing, WANG Chuanyang, LI Jiaqiang (2026). Effect of STL6/TiN Composite Coating on Corrosion Resistance of F347 Stainless Steel. Surface Technology (表面技术). https://doi.org/10.16490/j.cnki.issn.1001-3660.2026.12.007
Research & Educational Purpose Only: The translations, structured abstracts, analytical annotations, and data reports provided by SinoTechIntelare intended exclusively for academic research, internal corporate R&D, and educational benchmarking. They do not constitute formal engineering, chemical safety, legal, or professional advice.
Copyright & Intellectual Property Notice: Original copyright of the underlying source articles and experimental data remains with the respective authors, institutions, and original publishing journals. SinoTechIntel claims intellectual property only over its proprietary translations, analytical syntheses, and AEO structured enhancements in accordance with international fair use and academic citation principles.
Frequently Asked Questions
What is the primary failure mechanism of the F347 substrate under the tested conditions, and how does the composite coating mitigate it?
The F347 substrate exhibited extensive deep pitting due to chloride attack, which leads to localized metal dissolution and potential structural failure. The STL6/TiN composite coating mitigates this by forming a stable Cr₂O₃ passive film on the STL6 layer and providing an additional physical barrier with TiN, reducing the corrosion current density to 0.37 μA/cm² and raising the passivation potential to 939 mV, thereby suppressing pit initiation and growth.
How does the adhesion and microstructural integrity of the STL6/TiN coating compare to conventional single-layer coatings?
The plasma transferred arc deposition of STL6 results in a metallurgically bonded interface with elemental diffusion, as confirmed by EDS. The STL6 layer has a graded microstructure from planar/equiaxed grains at the substrate to columnar dendrites and fine equiaxed grains at the surface, with minimal oxide content. This defect-free interface ensures strong adhesion, unlike conventional coatings that may suffer from delamination or poor bonding.
What are the economic and scalability implications of implementing this two-step coating process for industrial components?
While the two-step process adds cost compared to single-layer coatings, the significant improvement in corrosion resistance—evidenced by the lowest corrosion current density (0.37 μA/cm²) and highest passivation potential (939 mV)—can extend component service life and reduce maintenance downtime. The process is compatible with existing plasma welding and CVD infrastructure, making it scalable for high-value components in nuclear and chemical plants where failure costs are high.
How does the corrosion performance of the STL6/TiN composite compare to the STL6 single-layer coating in terms of passive film stability?
The STL6 single-layer coating formed an oxide film but still exhibited intergranular corrosion. In contrast, the STL6/TiN composite coating showed only sparse shallow pits and the highest passivation potential (939 mV) and largest impedance modulus |Z|, indicating a more stable and protective passive film. The TiN topcoat likely seals defects and reduces the exposed area for corrosion, enhancing overall stability.
What are the long-term durability concerns for the TiN topcoat under mechanical wear or thermal cycling?
The TiN coating is hard and chemically inert, but its long-term durability under mechanical wear or thermal cycling depends on the adhesion to the STL6 underlayer and the matching of thermal expansion coefficients. The study did not specifically test wear or thermal cycling, but the metallurgical bond and graded microstructure of the STL6 layer are expected to provide a compliant base that reduces stress concentrations, potentially mitigating spallation. Further testing is recommended to validate performance in such conditions.
Related Chinese Research & Cross-Citations
Research Progress and Prospects of Corrosion-resistant High-entropy Alloy Coatings
Marine environments impose combined electrochemical, microbiological, and cavitation erosion degradation on metallic infrastructure, shortening service intervals and inflating maintenance expenditure. High-entropy alloy (HEA) coatings mitigate these failure modes through simple solid-solution or amorphous microstructures that suppress galvanic coupling and promote dense passive film formation. This review systematically examines corrosion-resistant HEA coatings from single-factor to multi-factor coupling perspectives, covering classification and compositional design, fabrication routes, and corrosion behavior under complex marine conditions. Key coating systems include FeCoCrNiMn, AlCoCrFeNi, FeCrNiCoAl, and (FeCoCrNi)75B15Si10 amorphous alloys deposited by atmospheric plasma spraying, high-velocity oxy-fuel spraying, and wire arc spraying. Elemental additions of Cr, Al, and Mo enhance passivation; B and Si promote amorphous phase formation. The review identifies core engineering bottlenecks: compositional design, process optimization, and service performance validation. A multi-scale simulation, process-structure optimization, and in-situ characterization framework is proposed to accelerate coating deployment. These findings provide theoretical and technical guidance for next-generation corrosion-resistant coatings in marine equipment.
Effect of Sodium Hypochlorite Concentration and Medium Temperature on Corrosion of 45# Steel in Artificial Seawater and Simulated Concrete Pore Solution
Seawater discharged during LNG regasification carries residual chlorine, predominantly sodium hypochlorite (NaClO), and low temperature, posing a dual corrosion threat to carbon steel components and adjacent reinforced concrete. This study systematically evaluates the corrosion behavior of 45# steel in artificial seawater (AS) and simulated concrete pore solution (SCPS, pH≈10) under NaClO concentrations of 0, 1, 10, and 100 mg/L at 10 °C and 25 °C. Electrochemical impedance spectroscopy, potentiodynamic polarization, weight-loss measurements, and localized corrosion-depth analysis were combined with SEM, EDS, XPS, and XRD to resolve corrosion kinetics, morphology, and product composition. In AS at 25 °C, increasing NaClO from 0 to 100 mg/L decreased charge transfer and film resistance (Rct + Rf) from 2266 to 1207 Ω·cm² and increased corrosion current density (Jcorr) from 11.48 to 18.29 μA/cm². Weight-loss rates remained 0.108 mm/a at 0 and 1 mg/L NaClO, rose slightly to 0.123 mm/a at 10 mg/L (+13%), and sharply to 0.202 mm/a at 100 mg/L (+87%). Corrosion morphology shifted from localized to uniform, with reduced pit depth. In SCPS at 25 °C, the alkaline environment suppressed NaClO-induced acceleration: Rct + Rf decreased from 2922 to 2266 Ω·cm², and weight-loss rates increased only 8% (0.0937 mm/a) at 10 mg/L and 25% (0.108 mm/a) at 100 mg/L relative to the 0.0865 mm/a control. However, 100 mg/L NaClO in SCPS significantly deepened localized pits. At 10 °C, both media exhibited reduced corrosion current density, thinner product layers, and shallower pits. Under standard discharge conditions (residual chlorine ≤0.2 mg/L), the additional corrosion risk from cold discharge water is negligible.
Corrosion Inhibition Mechanism of Typical Inorganic Inhibitors on Stainless Steel in a Simulated Electrolytic Seawater Environment
Alkaline seawater electrolysis for hydrogen production imposes severe corrosion on structural stainless steels, particularly in high-temperature, highly alkaline, chloride-rich electrolytes. This study evaluates four inorganic inhibitors—sodium molybdate (Na2MoO4), sodium tungstate (Na2WO4), sodium phosphate (Na3PO4), and vanadium pentoxide (V2O5)—for 316L austenitic stainless steel (316L SS) and 2205 duplex stainless steel (2205 DSS) in a simulated electrolytic seawater environment (6.0 mol/L NaOH, 2.0 mol/L NaCl, 90 °C). Potentiodynamic polarization, electrochemical impedance spectroscopy (EIS), and 14-day immersion tests quantified inhibition efficiency (IE). Surface morphology and film chemistry were characterized by SEM, optical profilometry (OP), and XPS. V2O5 exhibited the highest IE, reaching 79.90% for 316L SS and 89.58% for 2205 DSS at 0.05 mol/L, followed by Na3PO4 (83.33% for 2205 DSS). Na2MoO4 and Na2WO4 were least effective. EIS fitting revealed that V2O5 markedly increased film resistance (Rf) and charge-transfer resistance (Rct) (e.g., Rct = 29,770 Ω·cm², Rf = 923.50 Ω·cm² for 316L SS), indicating suppressed interfacial charge transfer. XPS confirmed the incorporation of V4+/V5+ and PO4³− species into the surface film, forming a dense, barrier-type vanadium/phosphate composite layer that mitigates corrosion. These findings establish V2O5 and Na3PO4 as promising inhibitors for stainless steel in harsh alkaline electrolytic seawater systems.
Influence of Temperature on Diffusion Behavior and Infiltration Layer Structure of Sherardizing on Structural Steel
Powder sherardizing on Q235 structural steel was conducted in a 70wt.% Zn–0.8wt.% NH4Cl–29.2wt.% α-Al2O3 activated pack at 340–400 °C for 2–10 h to establish the temperature-dependent growth kinetics, phase evolution, and corrosion performance of Zn–Fe intermetallic layers. Cross-sectional SEM/EDS and XRD show that all layers consist of δ and Γ phases, with Γ concentrated near the substrate; excessive Γ at 340 °C initiates interfacial cracking. Layer thickness increases monotonically with temperature and time, rising from 10.80 μm at 340 °C to 43.90 μm at 400 °C after 6 h, and from 12.10 μm at 2 h to 81.60 μm at 10 h at 380 °C. The Zn/Fe ratio and δ-phase fraction increase with temperature, yielding denser layers and improved corrosion resistance; at 380–400 °C, corrosion current densities fall to 1.16×10⁻⁶–9.78×10⁻⁷ A/cm². The diffusion coefficient at 380 °C is 2.341×10⁻¹³ m²/s. Prolonged holding beyond 6 h produces through-thickness cracks. DSC and microstructural evidence support a three-stage growth mechanism: formation of active Zn atoms via ZnCl2 decomposition, bidirectional Zn/Fe interdiffusion along substrate defects, and continuous inward advancement of the Zn–Fe intermetallic front. The optimal processing window is 380 °C for 6 h, yielding a ~36.1 μm crack-free layer with 84.1% δ phase and superior corrosion resistance.
Research Progress and Problem Analysis on Corrosion Prediction of Supercritical CO2 Transport Pipelines
Pipeline transport is the core of large-scale CO2 delivery in CCUS projects, and supercritical pipeline transport is the most economical and feasible method. However, inherent multicomponent impurities and complex aqueous phase precipitation make corrosion control difficult and costly. This review assesses corrosion mechanisms and prediction technologies for supercritical CO2 transport pipelines, focusing on numerical analysis, supporting experiments, and field application within comprehensive mechanistic models. Current understanding has clarified the effects of individual impurities (H2O, H2S, O2, SO2, N2O, N2, H2, CH4) and operating parameters, but synergistic mechanisms of mixed gases remain unresolved, lacking systematic quantitative description. Existing prediction models are limited in applicability to corrosion conditions, morphological matching, and comprehensiveness of factors. Experimental methods suffer from insufficient reliability, particularly in precise metering and replenishment of corrosive media under low water content and multicomponent impurity synergy. Field application faces challenges in rational model use and accurate extraction of field data. Future directions include: deepening research on synergistic effects of impurity gases and quantifying them via theoretical analysis to establish mapping between impurity concentration and corrosion rate; accelerating development of aqueous phase precipitation and distribution models, multicomponent impurity water chemistry models, thermodynamic and kinetic models for multicomponent reactions, and competitive formation/growth models for multiple product films; strengthening experimental techniques for precise metering and replenishment under low water and multicomponent synergy; and improving field application by understanding model parameter physical meanings, applicability boundaries, and ensuring reasonable input parameters and accurate field data extraction.
Research on Wear Resistance and Wear Mechanism of NM500 Steel in a Wide Temperature Range
The tribological behavior of NM500 wear-resistant steel was systematically evaluated across a wide temperature range from −50 to 600 °C to elucidate the influence of temperature on wear resistance and to provide a theoretical basis for service life extension. Friction and wear tests were conducted using a high-temperature tribometer under a normal load of 150 N, rotational speed of 354 r/min, wear track diameter of 15 mm, and test duration of 60 minutes. The microstructure was characterized by SEM and EBSD, while worn surfaces were analyzed using XRD, SEM, and 3D laser confocal microscopy. NM500 steel exhibits a fine lath martensitic structure with a grain size of 7.08 μm, conferring high hardness and superior wear resistance. At cryogenic temperatures (−50, −25, 0 °C), the wear mechanism is predominantly abrasive wear, with a wear rate of only 1.29×10−6 mm3/(N·m). As temperature increases, oxide formation on the worn surface intensifies, friction coefficient decreases to a minimum of 0.3 (50% lower than at low temperature), and wear rate increases significantly: 18×10−6, 22.7×10−6, 46.7×10−6, and 128×10−6 mm3/(N·m) at 100, 200, 300, and 600 °C, respectively. The dominant wear mechanism transitions from abrasive wear at low temperatures to oxidative wear with adhesive wear at elevated temperatures. At 600 °C, thermal softening, reduced texture strength, and oxide film delamination exacerbate material loss, shifting the mechanism to oxidative wear as the primary mode with adhesive wear as secondary.