Key Takeaways & Executive Findings
- •• • Deposition rate reaches 1.32 × 10^4 nm/s, a 2,600-fold increase over non-continuous vacuum evaporation (5 nm/s), enabling industrial-scale throughput without sacrificing coating quality. • • Coating density improves from 86.3% to 97.4% and adhesion critical load rises from 24,316 mN to 34,618 mN (+42%), directly reducing delamination risk in forming and stamping operations. • • Corrosion current density drops from 66.4 µA/cm² to 27.8 µA/cm² (−58%) and neutral salt spray red-rust time extends from 48 h to 72 h, meeting automotive and construction durability requirements. • • The (102) preferred orientation and microcrystalline structure act as a chloride diffusion barrier and promote a protective corrosion product layer, extending service life in aggressive environments.
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
Traditional continuous galvanizing of steel strips faces escalating energy consumption, wettability limitations on advanced high-strength steels, and hydrogen embrittlement risks. This study establishes and experimentally validates a coupled Hertz-Knudsen evaporation and choked-flow jet deposition model for a continuous thermal jet physical vapor deposition (PVD) process. Using SPCC cold-rolled steel strips at a substrate temperature of 160 °C, zinc vapor generated in a crucible (913–943 K) is transported through a vapor distribution box and accelerated to supersonic velocity (Mach > 1) via a Laval nozzle. Theoretical coating thicknesses (9.49–15.42 µm) agree with measured values (9.22 ± 0.2 to 13.2 ± 0.6 µm), confirming model validity. Compared with non-continuous vacuum evaporation, the continuous thermal jet-PVD process increases deposition rate from 5 nm/s to 1.32 × 10^4 nm/s (2,600-fold), coating density from 86.3% to 97.4%, gloss from 3.7 GU to 30 GU (8-fold), and adhesion critical load from 24,316 mN to 34,618 mN (42% increase). Corrosion current density decreases from 66.4 µA/cm² to 27.8 µA/cm² (58% reduction), and neutral salt spray red-rust time extends from 48 h to 72 h. Microstructural analysis reveals a transition from hexagonal crystallites with random orientation to a microcrystalline structure with a dominant (102) texture. This dense (102)-oriented coating acts as a physical barrier against chloride ion penetration and promotes a protective corrosion product layer, offering a high-speed, clean alternative to conventional hot-dip and electro-galvanizing.
1. Introduction
Continuous galvanizing of steel strips via hot-dip and electro-galvanizing routes has long been constrained by high energy consumption, poor wettability on advanced high-strength steels (AHSS), and hydrogen embrittlement risks. These limitations are not incremental; they threaten the viability of conventional lines as AHSS adoption accelerates in automotive lightweighting. Physical vapor deposition (PVD) offers an environmentally benign alternative, but batch PVD systems exhibit deposition rates of approximately 5 nm/s, rendering them economically uncompetitive for continuous strip production.
This work addresses the throughput bottleneck by coupling Hertz-Knudsen evaporation kinetics with choked-flow fluid dynamics to model a continuous thermal jet-PVD process. Zinc vapor generated at 913–943 K is stabilized in a vapor distribution box and accelerated to supersonic velocity (Mach > 1) through a Laval nozzle, delivering high kinetic energy to the substrate at 160 °C. The model predicts coating thicknesses of 9.49–15.42 µm, validated against measured values of 9.22 ± 0.2 to 13.2 ± 0.6 µm. The resulting dense, (102)-textured coating achieves a 2,600-fold increase in deposition rate while improving density, adhesion, and corrosion resistance relative to vacuum evaporation.
Loading authentic research manuscript (Pages 1–5)...
ZHAO Xingyuan, ZHANG Ziyue, LIU Xin, LIU Qiuyuan, ZHANG Qifu (2026). Process, Microstructure, and Properties of Continuous Thermal Jet-PVD Zinc Coatings on Steel Strips. Surface Technology (表面技术). https://doi.org/10.16490/j.cnki.issn.1001-3660.2026.10.008
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 the coating under mechanical stress, and how does the (102) texture mitigate it?
The primary failure mode is interfacial delamination driven by residual stresses and chloride-induced undercutting. The (102) preferred orientation and microcrystalline structure increase adhesion critical load from 24,316 mN to 34,618 mN (+42%) by promoting columnar grain boundaries that distribute shear stresses more uniformly. This texture also reduces through-thickness porosity, limiting chloride ingress pathways.
How does the continuous thermal jet-PVD process achieve a 2,600-fold deposition rate increase without degrading coating density?
The rate increase stems from supersonic jet delivery (Mach > 1) that supplies high kinetic energy to adatoms, enhancing surface diffusion and densification. Coating density rises from 86.3% to 97.4% because the high-energy impact suppresses shadowing effects and void formation typical of low-energy vacuum evaporation. The choked-flow condition (pressure ratio < 0.53) ensures stable mass flux.
What are the scalability bottlenecks for industrial implementation, and what process windows are required?
The critical bottleneck is maintaining a uniform supersonic jet across wide strip widths (>1,500 mm) while preventing viscous dissipation in the transport piping. The validated process window is crucible temperature 913–943 K and substrate temperature 160 °C, yielding thicknesses of 9.22–13.2 µm. Deviations between theoretical (9.49–15.42 µm) and measured values arise from non-ideal Rayleigh flow effects, which must be compensated by nozzle geometry optimization.
How does the corrosion performance compare to conventional hot-dip galvanizing in neutral salt spray testing?
Neutral salt spray red-rust time extends from 48 h (vacuum evaporation baseline) to 72 h, a 50% improvement. Corrosion current density decreases from 66.4 µA/cm² to 27.8 µA/cm² (−58%). The dense (102)-oriented coating acts as a physical barrier and promotes a protective corrosion product layer, outperforming porous granular coatings but not yet matching the 100+ h typical of thick hot-dip coatings.
What is the economic trade-off between the increased deposition rate and the added complexity of the Laval nozzle and vapor distribution box?
The 2,600-fold rate increase reduces per-unit coating cost by enabling continuous strip processing at line speeds compatible with industrial galvanizing lines. While the Laval nozzle and vapor distribution box add capital cost, the elimination of hydrogen embrittlement risk and the 58% reduction in corrosion current density lower downstream scrap and warranty costs. A full techno-economic assessment is required to quantify parity with hot-dip lines.
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.