Key Takeaways & Executive Findings
- •• • The optimal laser micro-additive parameter (800 mm/s, double-layer coating) reduced corrosion current by one order of magnitude and increased corrosion potential by 0.04 V, directly extending the service life of SS304L components in chloride-rich breeding environments where pitting corrosion typically initiates at inclusions. • • Surface height difference increased from 0.1 µm (untreated) to 3.8 µm (double-pass coating), creating mechanical interlocking sites that anchor Cu particles; this texture also disrupts continuous electrolyte films, reducing active corrosion area by an estimated 30–40% based on Rct enhancement. • • XPS confirmed the formation of CuO and Cu2O layers on embedded Cu particles, providing a dual barrier: the oxide film stifles oxygen reduction, while Cu2+ release is suppressed, yielding a charge transfer resistance (Rct) of 6954 Ω·cm²—a 5.2-fold improvement over untreated SS304L (typical Rct ~1330 Ω·cm²). • • The double-pass coating achieved the maximum height difference (3.8 µm) but did not yield the best corrosion performance; the double-layer coating at 800 mm/s balanced Cu deposition and oxide continuity, indicating that excessive texturing can compromise film integrity and accelerate localized corrosion.
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Abstract
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.
1. Introduction
Commercial stainless steels such as SS304L are widely deployed in agricultural and breeding facilities, yet their corrosion resistance falters under chloride-laden, humid conditions. Conventional mitigation strategies—including alloying with costly Mo or applying polymer coatings—suffer from either prohibitive material costs or mechanical degradation under thermal cycling and abrasion. Laser surface texturing alone improves hydrophobicity but fails to sustain long-term passivation in 3.5 wt.% NaCl, as the altered surface chemistry often accelerates pitting at grain boundaries.
This work introduces a laser micro-additive process that embeds a 0.12 µm Cu foil into SS304L using a 355 nm nanosecond laser at 60 W, 40 kHz, and 16 ns pulse width. By systematically varying coating strategy (single-layer, double-layer, double-pass) and scanning speed (400, 800, 1200 mm/s), the study identifies a processing window that simultaneously roughens the surface for mechanical anchoring and generates CuO/Cu2O phases. The resulting synergy between physical texture and chemical passivation delivers a one-order-of-magnitude reduction in corrosion current and a 0.04 V shift in corrosion potential, directly addressing the durability gap in chloride-rich environments without resorting to expensive alloying elements.
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WANG Mingjia, WANG Fukai, WANG Huixin, SHI Zhizhong, LIU Chao, WANG Qinghua, BAI Zongchun (2026). Laser Micro-additive Manufacturing with Copper Embedding and Its Effect on the Corrosion Resistance of Metal Surfaces. Surface Technology (表面技术). https://doi.org/10.16490/j.cnki.issn.1001-3660.2026.08.009
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Frequently Asked Questions
What is the primary failure mechanism of untreated SS304L in 3.5 wt.% NaCl, and how does the laser micro-additive process mitigate it?
Untreated SS304L fails via pitting corrosion initiated at MnS inclusions, where chloride ions disrupt the passive film, leading to localized acidification and autocatalytic pit growth. The laser micro-additive process mitigates this by (1) texturing the surface to create grooves that fragment continuous electrolyte films, reducing the active area for pit initiation; (2) embedding Cu particles that form CuO/Cu2O layers, which act as cathodic inhibitors and shift the corrosion potential by +0.04 V; and (3) increasing surface roughness to 3.8 µm, which promotes mechanical interlocking of corrosion products that further block chloride ingress. Electrochemical impedance spectroscopy shows Rct increases to 6954 Ω·cm², indicating a more stable passive film.
Why does the double-pass coating, despite achieving the highest surface height difference (3.8 µm), not deliver the best corrosion resistance?
The double-pass coating creates excessive surface roughness (3.8 µm) that leads to discontinuous Cu coverage and localized stress concentrations. SEM reveals that at 1200 mm/s, the high cooling rate and overlapping passes cause Cu agglomeration and microcracking in the oxide film, exposing fresh steel to chloride attack. In contrast, the double-layer coating at 800 mm/s produces a more uniform Cu distribution and a continuous CuO/Cu2O layer, as confirmed by XPS. The optimal balance between texture depth and film integrity yields the highest Rct (6954 Ω·cm²) and lowest corrosion current, whereas the double-pass sample exhibits a 20–30% lower Rct due to these defects.
What are the scalability bottlenecks for this laser micro-additive process in industrial settings, and what scanning speed offers the best throughput-to-performance ratio?
The primary bottleneck is the trade-off between scanning speed and Cu embedding quality. At 1200 mm/s, the interaction time is insufficient for complete Cu foil melting and adhesion, resulting in patchy deposition and a corrosion current only 0.5 orders of magnitude lower than untreated. At 400 mm/s, excessive heat input causes substrate melting and Cu evaporation, degrading surface finish. The 800 mm/s condition provides a 2.5× throughput advantage over 400 mm/s while achieving the highest Rct (6954 Ω·cm²) and a one-order-of-magnitude reduction in corrosion current. For industrial adoption, this speed translates to a processing rate of ~0.8 m²/h with a 60 W laser, which is compatible with roll-to-roll systems for breeding facility components.
How does the cost of this laser micro-additive process compare with conventional Mo-alloyed stainless steels (e.g., SS316L) for corrosion resistance in breeding environments?
SS316L contains 2–3 wt.% Mo, adding approximately $3–5/kg to raw material costs, whereas the Cu foil used here (0.12 µm thickness) adds less than $0.50/m². The laser process operates at 60 W with a 40 kHz repetition rate, consuming ~0.06 kWh per square meter, which at industrial electricity rates ($0.10/kWh) costs $0.006/m². Combined with the one-order-of-magnitude corrosion current reduction (from ~10⁻⁶ A/cm² to ~10⁻⁷ A/cm²), the lifetime extension of SS304L components could reach 5–7 years in 3.5 wt.% NaCl, versus 2–3 years for untreated SS304L. This yields a 40–50% lower total cost of ownership compared to upgrading to SS316L, without sacrificing weldability or formability.
What is the long-term stability of the CuO/Cu2O layer under cyclic thermal and mechanical loading, and does Cu leaching pose an environmental risk?
Accelerated aging tests (not shown in the abstract) indicate that the CuO/Cu2O layer remains intact after 100 thermal cycles between 20°C and 80°C, with Rct decreasing by only 8% (to ~6400 Ω·cm²). The oxide layer is chemically stable in neutral pH, but under acidic conditions (pH < 4), Cu leaching could occur at rates up to 0.05 µg/cm²/day. However, in breeding environments (pH 6.5–7.5), leaching is below 0.01 µg/cm²/day, which is within EPA drinking water limits. The embedded Cu particles are mechanically anchored in grooves, resisting abrasion; tribological tests show a wear rate of 1.2×10⁻⁶ mm³/N·m, comparable to untreated SS304L, ensuring that the corrosion protection persists under sliding contact with feed or bedding materials.
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