Key Takeaways & Executive Findings
- •• • At 1050 °C and 80 vol.% water vapor, the spinel oxide fraction in the TGO of APS-sprayed bond coats increased markedly compared to 0 vol.% and 45 vol.% conditions, confirming that water vapor accelerates outward diffusion of metal ions and spinel growth; this directly threatens coating durability in hydrogen-blended turbines where steam partial pressures are high. • • HVOF-sprayed bond coats with dense lamellar interfaces reduced spinel oxide formation relative to APS-sprayed coats, because the porous, weakly bonded APS lamellae provide fast diffusion pathways for corrosive species; industrial adoption of HVOF for bond coat deposition can therefore extend TBC service intervals under high water vapor exposure. • • The NiCoCrAlTaY bond coat generated the lowest spinel oxide content after 100 h at 1050 °C across all water vapor levels, as Ta promotes rapid formation of a stable Al2O3 scale and suppresses diffusion of other metal cations; this composition offers a viable route for turbines operating with high humidity or hydrogen combustion, though performance above 1050 °C remains unverified. • • All TBC systems formed a dual-layer oxide scale with continuous, dense Al2O3 beneath uneven, porous spinel oxide; the spinel's brittleness and accelerated growth rate readily initiate cracks within the TGO, leading to premature failure, so controlling spinel content is a direct lever for extending coating life in commercial gas turbines.
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 high-temperature water vapor corrosion behavior of MCrAlY/8YSZ thermal barrier coatings (TBCs) was investigated to address the premature failure of bond coats in hydrogen-blended gas turbine environments. Four MCrAlY bond coats with distinct compositions and microstructures were deposited on MM247 substrates via high-velocity oxy-fuel (HVOF) spraying and atmospheric plasma spraying (APS), followed by APS-deposited 8YSZ ceramic top coats. Corrosion tests were conducted at 1050 °C for 100 h under water vapor contents of 0 vol.%, 45 vol.%, and 80 vol.%. Scanning electron microscopy and energy-dispersive spectroscopy revealed a dual-layer oxide scale consisting of spinel oxides and Al2O3 on all samples. The Al2O3 layer exhibited a continuous, dense microstructure, whereas the spinel oxide grew unevenly with internal porosity. Increasing water vapor content from 0% to 45% and then to 80% progressively elevated the spinel oxide fraction, accelerating bond coat degradation. HVOF-sprayed bond coats, characterized by dense lamellar interfaces, effectively suppressed inward penetration of corrosive species and outward diffusion of metal ions, yielding significantly lower spinel content than APS-sprayed counterparts. The addition of Ta promoted rapid formation of a stable Al2O3 scale and inhibited outward diffusion of other metal cations, with the NiCoCrAlTaY bond coat producing the lowest spinel oxide content and superior protection. These findings indicate that dense bond coat microstructures and Ta alloying are critical for extending TBC service life in high-humidity or hydrogen-blended combustion environments.
1. Introduction
Commercial gas turbine engines increasingly face operational demands that degrade thermal barrier coatings faster than legacy design assumptions permit. Hydrogen-blended combustion and high-humidity environments introduce elevated water vapor partial pressures at temperatures exceeding 1000 °C, conditions under which conventional MCrAlY bond coats form mixed oxide scales rather than the desired pure, slow-growing Al2O3. The resulting spinel oxides are brittle, porous, and grow at accelerated rates, driving early crack initiation within the thermally grown oxide and triggering premature spallation of the ceramic top coat. Existing APS-deposited bond coats, while cost-effective, contain inter-lamellar porosity and weak splat interfaces that serve as fast diffusion paths for both inward oxygen transport and outward metal cation migration, exacerbating spinel formation.
This study systematically isolates the effects of bond coat microstructure and composition on high-temperature water vapor corrosion by comparing four MCrAlY variants deposited via HVOF and APS, each topped with an APS 8YSZ ceramic layer. Testing at 1050 °C for 100 h under 0, 45, and 80 vol.% water vapor quantifies how steam content alters spinel-to-Al2O3 ratios and identifies the mechanisms by which dense HVOF structures and Ta alloying suppress cation diffusion. The experimental protocol directly addresses the bottleneck of premature TGO failure in hydrogen-capable turbines, providing empirical thresholds for bond coat selection and pointing toward alloying strategies that maintain a single, stable Al2O3 scale under severe water vapor attack.
Loading authentic research manuscript (Pages 1–5)...
ZHANG Xiao, SU Jianhao, SHEN Hongyu, LIU Guanghua, CHEN Weijie, WANG Lu, XIAO Fei, WANG Jingyang (2026). Investigation on High Temperature Water Vapor Corrosion Behavior of MCrAlY/8YSZ Thermal Barrier Coatings. Surface Technology (表面技术). https://doi.org/10.16490/j.cnki.issn.1001-3660.2026.08.003
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 dominant failure mechanism of MCrAlY/8YSZ TBCs under high-temperature water vapor, and how does spinel oxide content quantitatively affect coating life?
The dominant failure mechanism is crack initiation within the thermally grown oxide (TGO) driven by uneven, porous spinel oxide growth. After 100 h at 1050 °C, samples exposed to 80 vol.% water vapor showed a markedly higher spinel fraction than those at 0 vol.% or 45 vol.%, because water vapor accelerates outward diffusion of metal cations from the bond coat. The spinel oxide is more brittle and grows faster than the continuous, dense Al2O3 layer, creating stress concentrations that initiate cracks and lead to premature spallation. Controlling spinel content is therefore directly correlated with extended service life.
How does the deposition method (HVOF vs. APS) for the bond coat influence corrosion resistance under 80 vol.% water vapor at 1050 °C?
HVOF-sprayed bond coats exhibit a dense microstructure with well-bonded lamellar interfaces, which blocks inward penetration of water vapor and oxygen and suppresses outward diffusion of metal ions. In contrast, APS-sprayed bond coats contain significant porosity and poor inter-splat bonding, providing channels for corrosive species and cation migration. After 100 h at 1050 °C and 80 vol.% water vapor, APS-sprayed samples formed substantially more spinel oxide in the TGO than HVOF-sprayed samples, confirming that HVOF deposition significantly improves overall water vapor corrosion resistance.
What is the specific role of Ta in NiCoCrAlTaY bond coats, and what empirical evidence supports its protective effect?
Ta promotes rapid formation of a stable, continuous Al2O3 scale and itself forms stable oxides that inhibit the outward diffusion of other metal cations such as Ni, Co, and Cr. Among the four bond coat compositions tested, the NiCoCrAlTaY system produced the lowest spinel oxide content after 100 h at 1050 °C under all water vapor conditions (0, 45, and 80 vol.%). This indicates superior protection and suggests viability for high-humidity or hydrogen-blended turbine environments, although performance at temperatures above 1050 °C requires further investigation.
Can the experimental results be directly scaled to industrial gas turbine components, and what are the remaining scalability bottlenecks?
The 100 h isothermal tests at 1050 °C with controlled water vapor provide a controlled ranking of bond coat performance, but industrial components experience thermal cycling, mechanical loading, and longer exposure times. The key scalability bottleneck is reproducing the dense HVOF microstructure on complex 3D geometries without compromising bond coat uniformity. Additionally, the Ta-containing NiCoCrAlTaY composition increases raw material cost, and its long-term stability under cyclic conditions and temperatures exceeding 1050 °C has not been established. Pilot-scale validation on actual turbine blades is required before full adoption.
What water vapor content threshold triggers a step-change in spinel oxide formation, and what are the implications for hydrogen-blended combustion?
The data show a progressive increase in spinel oxide fraction as water vapor content rises from 0 vol.% to 45 vol.% and further to 80 vol.%. While no single sharp threshold was identified, the 45 vol.% condition already produced a measurable increase relative to the dry condition, and 80 vol.% caused a further significant rise. This suggests that even moderate steam levels in hydrogen-blended combustion (which can generate 30–60 vol.% water vapor) will accelerate bond coat degradation. Turbines designed for hydrogen blends must therefore specify dense HVOF bond coats and Ta-containing alloys to maintain a stable Al2O3 scale.
Related Chinese Research & Cross-Citations
Effect of Microstructural Evolution on Wear and Cavitation Erosion Resistance of Laser-cladded CoCrNiNbx Medium-entropy Alloy Coatings
Cavitation erosion and wear failure critically limit the service life of flow-passing components such as pump impellers, turbine blades, and propeller systems subjected to high-speed liquid impact and cyclic flow-induced stresses. This work aims to design a high-performance surface coating with enhanced hardness, wear resistance, and cavitation erosion resistance by tailoring the Nb content in a CoCrNi medium-entropy alloy (MEA) system. CoCrNiNbx (x = 0, 0.2, 0.4, 0.6, 0.8, 1.0, and 1.2) coatings were fabricated on 316L stainless-steel substrates with an FL020 fiber laser under identical processing parameters. The effect of Nb addition on the phase constitution, microstructure, mechanical properties, tribological behavior, and cavitation performance of the coatings was comprehensively investigated to determine the optimal composition for balanced mechanical and anti-erosion properties. Phase analysis by X-ray diffraction (XRD) showed that increasing Nb content promoted a transition from a single face-centered cubic (FCC) solid solution to a dual FCC + hexagonal close-packed (HCP) phase structure. The emergence and growth of the Nb-rich HCP phase were accompanied by pronounced lattice distortion and precipitation strengthening. Microstructural characterization using field-emission scanning electron microscopy (SEM) combined with energy-dispersive spectroscopy (EDS) revealed that Nb preferentially segregated along interdendritic regions, where fine HCP-phase precipitates gradually formed a semi-continuous strengthening network. Electron backscatter diffraction (EBSD) analysis further quantified grain size and phase distribution. The average microhardness of the coatings initially increased and then decreased with increasing Nb molar ratio x, peaking at 689 HV0.1 for x = 0.6, approximately 3.7 times that of the substrate. Wear performance followed the same trend. Cavitation erosion tests demonstrated that the CoCrNiNb1.0 coating exhibited optimal cavitation erosion resistance, with mass loss significantly lower than that of the 316L substrate, achieving an order-of-magnitude improvement. The optimal Nb addition (x = 0.6–1.0) balances strength and toughness, significantly enhancing the wear and cavitation erosion resistance of CoCrNi-based MEA laser-cladded coatings. This study provides experimental evidence and process references for engineering applications of CoCrNi-based MEA coatings in high-flow-velocity liquid impact environments.
Laser Micro-additive Manufacturing with Copper Embedding and Its Effect on the Corrosion Resistance of Metal Surfaces
This study addresses the corrosion failure of SS304L stainless steel in breeding environments by developing a laser micro-additive copper-embedded surface functionalization process. A 355 nm nanosecond laser with 60 W average power, 40 kHz repetition rate, and 16 ns pulse width was used to embed a 0.12 µm Cu foil onto SS304L substrates under three coating strategies: single-layer, double-layer, and double-pass, each at scanning speeds of 400, 800, and 1200 mm/s. Surface characterization via 3D profilometry, SEM, EDS, and XPS revealed regular grooves and micro-concave structures with height differences increasing from 0.1 µm (untreated) to 1.6–3.8 µm, with the double-pass sample achieving the maximum 3.8 µm. Cu particles were successfully embedded, forming CuO and Cu2O oxide layers. Electrochemical tests in 3.5 wt.% NaCl solution showed that the optimal sample (double-layer coating at 800 mm/s, designated b2) exhibited the highest corrosion potential (increased by ~0.04 V), a one-order-of-magnitude reduction in corrosion current, and a maximum charge transfer resistance (Rct) of 6954 Ω·cm². These results demonstrate that laser micro-additive embedding of copper synergistically enhances the corrosion resistance of stainless steel through surface texturing, copper particle incorporation, and oxide film formation.
Prediction of Geometric Characteristics of Laser Cladding Process by the GWO-BPNN Algorithm
Laser cladding is a green surface modification technology widely used in aerospace and other high-end fields, but traditional process optimization methods such as single-variable analysis and orthogonal experiments suffer from low efficiency and high cost. The geometric characteristics of the cladding layer—dilution rate, forming coefficient, and wetting angle—directly determine service performance. Existing machine learning models often fail to achieve multi-objective optimization and comprehensive prediction. This study proposes a hybrid algorithm combining Grey Wolf Optimizer (GWO) with Backpropagation Neural Network (BPNN) to predict geometric quality indicators. Full-factorial single-track laser cladding experiments were conducted on 316L stainless steel with 316L alloy powder. A polynomial regression model predicted clad width and height with relative error below 4.2%. The GWO-BPNN model predicted dilution rate, forming coefficient, and wetting angle with an average coefficient of determination (R²) of 95.28%, a 12.4% improvement over traditional BPNN (82.93%). Experimental and inverse validation confirmed stable predictive performance across different parameter ranges, meeting engineering tolerance requirements. The method provides a quantitative basis for multi-dimensional optimization of cladding quality and demonstrates practical applicability in industrial scenarios.
Scuffing Resistance of Carburized Gear Steel with Laser-cladded Ni-based Composite Coatings
Scuffing constitutes a rapid, catastrophic failure mode in high-speed, heavy-duty gear transmissions, and enhancing scuffing load capacity remains a critical challenge for high-power-density systems. This study investigates the feasibility of laser cladding to improve scuffing resistance and repair scuffed tooth surfaces on 18CrNiMo7-6 gear steel. Three substrate conditions—tempered, carburized, and carburized with pre-induced scuffing damage—were coated with NiCr20-3%ZrO2-1%MoS2 (mass fraction) via a MobiMRO-2 laser cladding system with synchronous powder feeding. The cladded layer, approximately 1.2 mm thick, exhibited a dendritic, cellular, and irregular particulate microstructure with hardness of 690–730 HV0.1, comparable to the carburized case. Laser cladding induced significant heat-affected zone (HAZ) transformations: tempered steel formed lath martensite and lower bainite near the coating, with spheroidized structures in the lower HAZ; carburized steel developed coarse acicular martensite at the top, refined structures in the middle, and troostite at the bottom, with overall temper softening. Scuffing tests using a two-disc rolling contact rig under step-wise loading revealed that cladded tempered, cladded carburized, and repaired samples achieved 94.4%, 61.3%, and 50.7% increases in scuffing load capacity, respectively, relative to uncladded carburized baseline. This enhancement stems from increased hardness and the self-lubricating effect of the coating, which reduced interfacial friction coefficient and delayed critical failure. Failure analysis showed that the cladded layer altered crack initiation and propagation paths, significantly raising the critical failure load. The repaired samples, however, exhibited poor bonding at the original damage interface, leading to localized coating detachment. These findings confirm laser cladding as an effective method for enhancing gear scuffing resistance and repairing scuffed surfaces, providing experimental and theoretical support for surface strengthening and damage repair.
Numerical Simulation and Process Parameter Optimization of Laser Hardening for QT500-7 Ductile Cast Iron
Laser surface hardening of QT500-7 ductile cast iron was investigated through a coupled finite element–machine learning–multi-objective optimization framework. A phase-transformation heat-transfer finite element model screened process windows for laser power (100–400 W), scanning speed (5–15 mm·s⁻¹), and overlap rate (60%–90%). A three-factor, three-level Box-Behnken design yielded hardened layer depth and fused layer depth as response variables. Four predictive architectures were benchmarked: Random Forest (RF), XGBoost, RF-XGBoost ensemble, and Bayesian-optimized RF-XGBoost (BO-RF-XGBoost). The BO-RF-XGBoost model achieved superior accuracy, with relative errors of 6.52% for hardened layer depth and 9.09% for fused layer depth. Multi-objective optimization compared Advantage Actor-Critic (A2C), Multi-Objective Particle Swarm Optimization (MOPSO), and Non-dominated Sorting Genetic Algorithm II (NSGA-II). A TOPSIS-entropy weight method ranked the Pareto front, identifying optimal parameters: laser power 230 W, scanning speed 14 mm·s⁻¹, overlap rate 75%. Experimental validation at these parameters produced a hardened layer depth of 230 μm and fused layer depth of 66 μm, with finite element model errors of 9.13% and 3.03%, respectively. Microhardness measurements showed the fused layer at 940 ± 40 HV0.5 and the hardened layer at 630 ± 30 HV0.5, both significantly exceeding the substrate hardness of 166 ± 15 HV0.5. The framework provides a reliable tool for parameter optimization in laser surface hardening of ductile cast iron.
Polishing of Glass-ceramics with Nano-silica Modified Magnetic Abrasives
Glass-ceramics, multiphase composites combining amorphous and crystalline phases, exhibit disparate mechanical responses that induce subsurface damage and surface defects during conventional polishing. This study fabricates magnetic abrasive particles (MAPs) via a bonding process with three variants: unmodified, hydrophilic nano-silica (20 nm) modified, and hydrophobic nano-silica (20 nm) modified. Base composition comprises iron powder (75 μm) and CeO2 abrasives (15 μm) at a 12:3 mass ratio. Polishing tests on glass-ceramics using an N-S array tool reveal that hydrophobic modified MAPs achieve the lowest surface roughness (Sa = 17 nm) and highest material removal depth (2.5 μm), compared to hydrophilic (Sa = 24 nm) and unmodified (Sa = 48 nm) MAPs. Dynamic friction coefficients measured in situ are 0.31, 0.35, and 0.42 for hydrophobic, hydrophilic, and unmodified MAPs, respectively. Surface and subsurface damage analyses show hydrophobic MAPs minimize pits, micro-cracks, and brittle fractures, while hydrophilic MAPs exhibit brittle spalling and unmodified MAPs show point defects. Wear tests confirm that nano-silica addition enhances bond strength and extends abrasive lifespan. The hydrophobic modification promotes surface hydration and formation of a lubricating silicate gel layer, reducing mechanical plowing and friction, thereby enabling high-quality surface integrity. These findings demonstrate that nano-silica modification effectively tunes MAP hydrophobicity, offering a viable route for ultra-smooth, low-damage polishing of glass-ceramics.