Low-temperature corrosion performance of laser cladded WB-Co coatings in acidic environment

Lele Han; Li Fan; Haiyan Chen; Guangkuo Zhu; Yujiang Qin; Qizheng Cao

doi:10.1515/htmp-2025-0082

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Low-temperature corrosion performance of laser cladded WB-Co coatings in acidic environment

Lele Han , Li Fan , Haiyan Chen , Guangkuo Zhu , Yujiang Qin und Qizheng Cao

Veröffentlicht/Copyright: 16. Juli 2025

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Abstract

In this investigation, cobalt-based composite coatings with varying concentrations of spherical tungsten boride (WB) were fabricated via laser cladding technology, specifically focusing on two compositional systems: Co + 15% WB and Co + 45% WB. The electrochemical behavior of these coatings was systematically evaluated in a low-temperature hydrochloric acid environment to elucidate the influence of WB content on the corrosion resistance mechanisms of cobalt-based coatings and to reveal the electrochemical corrosion mechanisms of WB-reinforced cobalt-based coatings. Experimental results demonstrated that all coatings, including pure Co, Co + 15% WB, and Co + 45% WB, exhibited distinct passivation behavior in 0.5 mol·L⁻¹ HCl solution. The passivation range for WB-containing coatings was predominantly observed between −0.1 V and 0.2 V. Comparative analysis revealed that the Co + 15% WB coating exhibited the most favorable corrosion resistance properties, characterized by the highest corrosion potential and the lowest corrosion current density (i _corr). Furthermore, this coating composition demonstrated superior passive film resistance, charge transfer resistance (R _ct), and film resistance (R _f), indicating optimal protective performance in acidic environments. In contrast, the EH40 substrate exhibited significant corrosion susceptibility in acidic solutions, with the corrosion process primarily dominated by anodic dissolution. These findings provide valuable insights for the design and optimization of corrosion-resistant coatings used in marine vessels operating in corrosive acidic environments.

Keywords: laser cladding; tungsten boride; electrochemical corrosion; corrosion resistance; low-temperature environment

1 Introduction

In the context of global climate change, the Arctic shipping routes are experiencing increased accessibility for commercial navigation, accompanied by a progressive rise in maritime traffic volume [1]. This transformation has elevated these routes from their historical strategic significance to prominent international commercial corridors. Nevertheless, the Arctic passage remains one of the most hazardous global shipping lanes due to its extreme environmental conditions, necessitating technological advancements for further development and utilization. The unique Arctic environment imposes stringent requirements on high-strength marine steels, demanding resistance to multiple stressors including ice abrasion, chloride-induced seawater corrosion, low-temperature fatigue degradation, and microbial-induced corrosion [2,3,4].

The electrochemical corrosion mechanisms at the ice-seawater interface are particularly noteworthy, where the formation of a liquid film at the ice-seawater boundary facilitates accelerated localized corrosion in low-temperature environments. These challenging conditions underscore the critical need for enhanced performance of structural materials, particularly EH40 steel, and their surface protection systems [5]. Recent advancements in materials science have identified novel boride ceramic materials with exceptional hardness and durability as promising candidates for such applications.

Laser cladding technology, with over three decades of development, has emerged as a transformative solution for technical repairs and component enhancement in traditional industries [6]. Extensive research has demonstrated that laser-clad metal matrix composites reinforced with ceramic particles significantly improve surface properties through various strengthening mechanisms, including phase transformation hardening, grain refinement, diffusion strengthening, and solid solution strengthening [7,8]. These processes collectively enhance the composite’s mechanical properties, wear resistance, corrosion resistance, and fatigue performance [9].

Transition metal borides, characterized by their exceptional hardness (HV > 40 GPa), wear resistance, and chemical stability, have garnered significant attention [10]. The unique electronic configuration of boron, capable of forming diverse covalent bonds (sp, sp2, sp3) and engaging in electron transfer reactions, enables the formation of numerous compounds with transition metals [11]. Tungsten borides (WB, WB₂, WB₃, WB₄) are known for their exceptional mechanical properties [12]. Recent advancements by Sun Shibo have led to the development of innovative WB-WCoB coatings, which demonstrate improved corrosion resistance [13]. The observed performance improvement mainly results from the electrochemical potential difference between phases, with WCoB demonstrating a more active electrochemical behavior compared to WB, as evidenced by their respective standard electrode potentials [12,14,15].

Complementary research by Issac et al. on Zn-MgO-WB composite coatings demonstrated superior corrosion resistance in simulated marine environments (3.5% NaCl), with corrosion rates as low as 0.0010482 mm·year⁻¹ [16]. Although the corrosion performance of Co-WB coatings under cryogenic conditions (−20°C) has garnered significant attention, detailed and systematic studies in this area are still scarce [17]. Notably, while spherical powder has been widely acknowledged as the optimal material for laser cladding applications, the principal innovation of this investigation resides in the synergistic implementation of a low-temperature processing environment coupled with the strategic incorporation of spherical WB particles. The research on Co-WB (Cobalt-Tungsten Boride) coatings provides foundational insights into their corrosion mechanisms in acidic environments, significantly advancing our understanding of their performance under such conditions [18]. This work systematically investigates the corrosion protection performance of Co-WB composite coatings in sub-zero conditions (−20°C) through complementary electrochemical characterization methods. The corrosion evolution in 0.5 mol·L⁻¹ HCl solution was rigorously examined through combined potentiodynamic polarization and EIS techniques, specifically probing the interfacial coupling mechanisms between WB phase distribution and cobalt matrix dissolution dynamics.

2 Materials and experimental procedures

2.1 Materials

The experimental materials consisted of EH40 cryogenic-grade steel, supplied by Baosteel (Shanghai, China), serving as the substrate material, and cobalt-based alloy powder, obtained from Höganäs (Shanghai, China), utilized as the cladding material.

The substrate specimens were prepared with dimensions of 300 mm × 300 mm × 40 mm to ensure sufficient surface area for cladding application and structural integrity during testing. The chemical composition of the EH40 steel substrate, determined through spectroscopic analysis, is presented in Table 1, with all elemental concentrations expressed in weight percentage (wt%).

Table 1

Detailed chemical composition of EH40 steel (wt%)

Elements	C	Mn	Si	Cr	Al	Nb	V	Mo	Ni	Ti	Cu	Fe
Content	0.160	0.900	0.150	0.200	0.015	0.020	0.100	0.080	0.400	0.020	0.350	Bal.

Table 2 presents the chemical composition of the cobalt-based alloy powder, with all elemental concentrations expressed in wt%.

Table 2

Detailed chemical composition of cobalt-based alloy powders (wt%)

Elements	C	W	Ni	Fe	Cr	Si	Co
Content	1.400	7.700	0.200	0.200	27.600	1.000	61.900

The boron carbide ceramic particles, utilized as the reinforcement phase within the composite coating, were sourced from Luoyang Jinlu Hard Alloy Co., Ltd, located in China. This material was procured through commercial channels to ensure consistency and quality for the experimental procedures.

2.2 Materials processing and analytical methodology

The cobalt-based alloy matrix composites were synthesized by precisely proportioning metallic constituents according to the formulations detailed in Table 3. Powder homogenization was achieved through mechanical blending using a QM-3SP4 planetary ball milling system (Nanda Instruments Co., Ltd) with a standardized 60 min processing duration, ensuring consistent particulate dispersion critical for subsequent thermal processing. Post-cladding specimens were sectioned using wire electrical discharge machining into standardized 10 mm × 10 mm × 5 mm parallelepipeds for electrochemical characterization, followed by sequential abrasive polishing (180-2000 grit SiC papers). Complementary analytical specimens (5 mm × 5 mm × 3 mm) were prepared through identical sectioning protocols for surface chemical analysis via X-ray photoelectron spectroscopy (XPS).

Table 3

Composition optimization and deposition parameters (wt%)

Samples	WB content (%)	Co powder content (%)
Co + 15%WB	15	85
Co + 45%WB	45	55
Co	0	100

The laser cladding experiment uses a high-power fiber laser (YLS-6000-S2T, IPG, USA), an output laser wavelength of 1,075 ± 5 nm, a maximum output power of 5.5 kW, and the stability of the work is less than 2%. The experimental powder feeding system is coaxial powder feeding, using a double cylinder powder feeder that can be sent to the powder size range of 20–200 µm. Argon (Ar) was selected as the powder-feeding medium to protect the cladding powder in the laser cladding process. Table 4 display the laser cladding process parameter.

Table 4

Laser cladding parameters

Laser power (kW)	Laser wavelength (nm)	Scanning speed (mm·s⁻¹)	Powder feed rate (g·min⁻¹)	Monitoring range (mm)	Spot diameter (mm)
5.5	1,080	16	33	460	5

2.3 Electrochemical corrosion resistance test

The corrosion resistance of the coatings was thoroughly evaluated using established electrochemical characterization methods. A comprehensive electrochemical evaluation protocol was implemented, encompassing potentiodynamic polarization tests and electrochemical impedance spectroscopy (EIS). These measurements were performed utilizing a CHI 600 E electrochemical workstation, produced by Shanghai Chenhua Instrument Co., Ltd, based in China.

Specimen preparation involved epoxy resin encapsulation to maintain a 1 cm² working surface area, with electrical connectivity ensured through soldered copper leads. Prior to electrochemical characterization, all samples underwent cryogenic conditioning at −20°C for 120 h in a controlled environment. The corrosive medium consisted of a 0.5 mol·L⁻¹ HCl solution maintained at ambient temperature (25 ± 1°C).

The three-electrode configuration employed in this study included: Coated metallic substrate (10 × 10 × 5 mm³); Saturated calomel electrode (SCE); and Platinum foil (15 × 15 mm²).

Polarization measurements were conducted with a scanning potential range from −1.0 V_SCE to +1.5 V_SCE at a controlled sweep rate of 2 mV·s⁻¹. To establish electrochemical equilibrium, specimens were immersed in the electrolyte for 30 min preceding each measurement. The electrochemical cell configuration maintained a 500 mL electrolyte volume with a controlled working surface area of 1 cm², while non-active surfaces were insulated using silicone sealant.

EIS investigations were performed under open-circuit potential conditions with a sinusoidal perturbation of 10 mV amplitude across the frequency spectrum of 10⁻²–10⁵ Hz. Acquired impedance data were analyzed using ZSimpWin software (Version 3.60) with appropriate equivalent circuit modeling. All experimental parameters and instrument configurations complied with ASTM G5-14 and ASTM G106-89 standards for electrochemical corrosion testing.

2.4 Analysis of corrosion products on the coating

The corroded coatings were characterized for surface chemistry using an ESCALAB 250Xi XPS (Thermo Fisher Scientific). The experimental procedure included the following steps: Samples measuring 5 mm × 5 mm × 3 mm were mounted in epoxy resin, ensuring the coated surface remained accessible for analysis. To induce accelerated corrosion, the specimens were immersed in a 0.5 mol·L⁻¹ HCl solution at −20°C for 360 h. XPS data were collected using monochromatic Al Kα radiation (hv = 1486.6 eV) in an ultra-high vacuum environment with a pressure below 5 × 10⁻⁹ mbar.

3 Results and discussion

3.1 Microstructure and phase composition of the coating

As illustrated in Figure 1(a)–(c), the elemental distribution of the coated Co + 15% WB reveals a significant enrichment of Co and W elements surrounding the spherical WB particles. The W element accounts for about 45% according to the mass fraction. A significant amount of WO₃ and SiO₂ is observed around the spherical WB particles, while certain carbide-enhanced phases are encapsulated by the solid solution γ-Co. According to the atomic ratio of the elements, the inter-dendritic organization is mainly Cr₇C₃, and the white dendritic organization is mainly Cr₂₃C₆. The elemental contents of the corresponding areas of the Co + 45% WB coatings are shown in Figure 1(d)–(f), and it is known from the corresponding areas of the elemental contents. Area 1 is mainly columnar crystals, containing a large number of elements such as Co, Cr, W, etc. The main composition of this area is carbide Cr₇C₃, WO₃, and part of the Fe element, mainly FeNi. Area 2 is a columnar inter-crystalline eutectic, with γ-Co accounting for the main composition, and the formation of diffuse reinforcement of Cr₇C₃ carbide and WO₃ in the γ-Co. With more WB, the cooling rate is slower and the carbide Cr₇C₃ forms and precipitates. Large particles within the molten pool restrict grain growth, promote compositional segregation, and disrupt the directional growth of columnar crystals.

Figure 1

EDS spectrum of laser cladding coatings on the surface: (a)–(c) Co + 15%WB; (d)–(f) Co + 45%WB; and (g)–(i) Co.

The element distribution of the corresponding area of the Co coating is shown in Figure 1(g)–(i), the organization of the surface is much finer and uniform, mainly composed of columnar dendrites and inter-dendritic organization, with no obvious defects. Area 1 is mainly a columnar dendritic organization, and a small amount of solid solution formed by FeNi₃ was detected in addition to the enhanced phase of Cr₇C₃ and Cr₂₃C₆ carbides to enhance the strength of the alloy by solid solution strengthening. The strength of the alloy was increased. The inter-dendritic organization in Area 2 is dominated by Cr₂₃C₆ and WO₃ according to the atomic ratios. The precipitation of Cr₂₃C₆ also depends on the cooling rate of the cladding layer, which is more likely to be precipitated under the effect of higher negative free energy generated in the molten pool when there is no obstruction by WB particles.

The substrate surface was modified through laser melting of spherical WB-enhanced cobalt-based coatings, which exhibited a dense microstructure free of significant pores or cracks. The coating enhancement effect is mainly due to the addition of spherical WB particles, and the particle phase is diffusely distributed in γ-Co as a second phase, which plays a supporting role for the cobalt matrix and strengthens the composite coating while improving the resistance to crack formation and growth. Different microstructures were generated with WB particles as the center outward, and equiaxed crystals were formed around the particles, mainly planar crystals and cellular crystals. Subsequently, they grew outward and formed columnar dendritic crystals, which solidified and grew up along the direction of heat flow toward the interior of the melting zone, and finally showed a certain arrangement of columnar dendritic crystal organization.

3.2 Potentiodynamic polarization results

Figure 2 comparatively displays the electrochemical polarization profiles recorded under potentiodynamic conditions for both the bare substrate and three protective coatings in a 0.5 mol·L⁻¹ HCl medium. Distinctive passivation characteristics emerged in the Co-WB composite system, with both 15 and 45% WB additions maintaining consistent anodic behavior. The cathodic current fluctuations exhibited material-independent similarity, while the developed passive films demonstrated potential-dependent stability between −0.1 and 0.2 V. The passivation range for the Co coating is longer, mainly due to the lower potential of Co, which leads to its initial corrosion in the corrosive solution and the formation of corrosion products. The open-circuit potentials of Co, Co + 45%WB, and Co + 15%WB coatings exhibit a sustained anodic shift during immersion. During electrochemical dissolution, alloy substrates undergo anodic oxidation with electron transfer, leading to metallic ion release. Notably, dissolved oxygen participates in interfacial reactions, promoting the in situ generation of passivating oxides (e.g., Cr₂O₃, WO₃, Cr₂Ni₃) that form compact surface films. These oxide layers act as diffusion barriers, significantly impeding charge/mass transfer during corrosion [19]. In contrast, EH40 steel demonstrates the most negative self-corrosion potential, undergoing severe anodic dissolution accompanied by extensive formation of corrosion by-products.

Figure 2

Polarization curves of coatings and substrate in 0.5 mol·L⁻¹ HCl solution.

The electrochemical parameters derived from Tafel extrapolation of polarization curves in 0.5 mol·L⁻¹ HCl are summarized in Table 5. The corrosion characteristics, including corrosion potential (E _corr), corrosion current density (i _corr), and polarization resistance (R _p), were quantitatively analyzed through electrochemical workstation software. Analysis reveals comparable E _corr values among Co + 15%WB, Co + 45%WB, and pure Co coatings, with the highest E _corr observed for Co-based coatings, demonstrating their superior protective performance in acidic environments. Surface morphology and compositional homogeneity significantly influence the corrosion resistance, where the incorporation of 15% WB optimizes the coating’s anti-corrosion properties.

Table 5

Polarization fitting results of coatings and substrate in 0.5 mol·L⁻¹ HCl Solution

Specimen	E _corr (mV)	i _corr (μA·cm⁻²)	R _p (kΩ)	β _a (V·dec⁻¹)	β _c (V·dec⁻¹)
Co + 15%WB	−313	14.340	1.781	3.623	13.400
Co + 45%WB	−319	29.840	1.076	2.334	11.210
Co	−330	62.770	0.575	3.707	8.340
EH40	−404	469.600	0.047	11.070	8.493

The i _corr values follow a distinct hierarchy: Co + 15%WB (14.34 μA·cm⁻²) < Co + 45%WB (29.84 μA·cm⁻²) < Co (62.77 μA·cm⁻²) < EH40 (469.6 μA·cm⁻²), confirming that the Co + 15%WB coating exhibits the lowest corrosion rate and optimal protection efficiency. In contrast, EH40 substrate undergoes severe degradation in acidic media. Kinetic analysis indicates predominant anodic control of the corrosion process, as evidenced by the higher anodic Tafel slope (β _a) compared to the cathodic slope (β _c).

3.3 EIS analysis

The EIS characteristics of the coatings and substrate in 0.5 mol·L⁻¹ HCl are illustrated in Figure 3 through Nyquist and Bode representations. The Nyquist spectra of Co + 15% WB and Co + 45% WB coatings display dual capacitive semicircles, encompassing a high-frequency capacitive loop attributable to the passive film response and a low-frequency Warburg impedance related to mass transport constraints. The diameter of the low-frequency capacitive arc, which is indicative of corrosion resistance, adheres to the following order: Co + 15% WB > Co + 45% WB > Co > EH40, highlighting the superior protective efficacy of the 15% WB-modified coating in acidic environments. Electrochemical analysis suggests that the corrosion mechanism entails the concurrent occurrence of anodic metal dissolution and cathodic oxidant reduction. The anodic polarization behavior demonstrates an exponential increase in current density within the activation region, which is governed by charge transfer kinetics.

Figure 3

Polarization curves of coatings and substrate in 0.5 mol·L⁻¹ HCl solution: (a) Nyquist plots; (b) Bode impedance plots and Bode angle plots.

Figure 4 shows the fitted circuit diagrams of electrochemical impedance of the three coatings and substrates in 0.5 mol·L⁻¹ HCl solution. Where R _s is the solution resistance; R _f is the passivation film resistance; Q _f is the passivation film capacitance, Q _dl is the double layer capacitance, R _ct is the electrochemical transfer resistance, W is the diffusive Warburg impedance, and L is the inductive impedance.

Figure 4

Electrochemical impedance fitting circuit diagrams for three coatings and substrate in 0.5 mol·L⁻¹ HCl solution: (a) Co + 15% WB and Co + 45% WB; (b) Co; and (c) EH40.

The equivalent circuit modeling results, as illustrated in Figure 4 and quantified in Table 6, were obtained through numerical fitting using ZSimpWin software. The electrochemical interfaces were described by distinct equivalent circuits: The Co + 15% WB and Co + 45% WB composites were modeled using the R(Q(RW(QR))) equivalent circuit configuration; Co coating composites were modeled using the R(Q(R(QR))) configuration; EH40 substrate composites were modeled using the R(QR(LR)) configuration.

Table 6

Electrochemical impedance fitting results of three coatings and substrates in 0.5 mol·L⁻¹ HCl solution

Samples	R _s (Ω·cm²)	Q _f		R _f (Ω·cm²)	W (S·sⁿ·cm⁻²)	L (H·cm⁻²)	Q _dl		R _ct (Ω·cm²)
Samples	R _s (Ω·cm²)	Y ₀ (Ω⁻¹·cm⁻²·sⁿ)	n _f	R _f (Ω·cm²)	W (S·sⁿ·cm⁻²)	L (H·cm⁻²)	Y ₀ (Ω⁻¹·cm⁻²·sⁿ)	n _dl	R _ct (Ω·cm²)
Co + 15%WB	2.989	8.090 × 10⁻⁵	0.886	9.789	5.256 × 10⁻⁴	—	7.215 × 10⁻⁴	0.908	8,356
Co + 45%WB	2.992	1.894 × 10⁻⁴	0.849	8.914	6.685 × 10⁻³	—	1.182 × 10⁻⁴	0.225	1,613
Co	4.204	7.421 × 10⁻⁵	0.379	1.391	—	—	6.195 × 10⁻⁵	0.886	788.600
EH40	10.070	1.008 × 10⁻⁴	1.000	1.440	—	405.100	2.314 × 10⁻⁴	0.790	36.810

Analysis of the fitted parameters reveals that Co + 15% WB exhibits the highest charge transfer resistance (R _ct) and film resistance (R _f) values among all specimens. This electrical behavior confirms the formation of a highly protective passive film on the Co + 15% WB surface, which accounts for its superior corrosion resistance performance.

This may be due to the fact that the thermal expansion coefficient of the hard particles (WB/W₂B₅) is different from that of the Co coating in the acidic solution with more Cl⁻ content, but with the addition of WB. More WB leads to uneven solidification and residual stresses, and pitting corrosion is prone to occur at interfacial defects. The values of R _ct of Co, Co + 45% WB and Co + 15% WB increase multiplicatively, and the values of R _ct of the three coatings are about 200, 50, and 20 times, respectively, compared to the substrate. The corrosion of EH40 is severe in acidic environments, and passivation film protection is not produced, and Co-based coatings have significant protection effects on the substrate [20]. The protective effect of Co-based coating on the substrate is obvious.

3.4 Surface analysis of WB-Co coating after corrosion

The corrosion behavior of the three coatings was investigated in a simulated acidic environment using a 0.5 mol·L⁻¹ HCl solution, which is rich in chloride ions [21]. Figure 5 presents the XPS full spectrum of the coatings after 360 h of immersion. The results indicate that the coatings experienced significant surface degradation under low-temperature conditions (−20°C) in the presence of high Cl⁻ concentrations. The corrosion resistance of these materials is closely associated with the dynamics of passive film formation, its breakdown, and subsequent repassivation. The primary elements identified in the corrosion products include W, C, Cr, Fe, and Co. Additionally, a variety of stable oxides and hydroxides were detected, which are typical of acidic environments. The Co and Cr elements are derived from the Co-based alloy matrix, while W originates from the oxidation of WB hard phases. Oxygen is primarily attributed to the formation of corrosion-related oxides. To further elucidate the chemical states of the corrosion products, narrow XPS spectra of key elements were analyzed to identify their specific valence states and compositions.

Figure 5

Full XPS spectra of three coatings immersed in 0.5 mol·L⁻¹ HCl solution for 360 h.

As shown in Figure 6, elemental Co has three main peaks with binding energy close to 782, 798, and 804 eV, respectively. The peak at 782 eV represents the 2p1/2 peak of Co²⁺ in Co(OH)₂. The peak at 798 eV is the 2p1/2 peak of the cobalt oxide (Co³⁺) in the form of Co₂O₃. The satellite peak at 804 eV corresponds to Co²⁺ in cobalt oxide (CoO). The peak at 715 and 721 eV represents the Fe 2p1/2 peak of Fe₃O₄. Co ions are more likely to form oxides in acidic environments. Element Fe mainly shows two peaks with binding energy close to 715 and 721 eV. The peaks represent Fe 2p1/2 in Fe₃O₄ and Fe 2p3/2 in Fe₂O₃, respectively. Element Cr mainly presents two peaks with binding energy close to 577 and 587 eV. The two peaks represent Cr³⁺ in Cr(OH)₃ Cr 2p3/2 and Cr 2p1/2 peaks. The corrosion products of elemental Cr are mainly formed as hydroxides in acidic HCl solution. Elemental W mainly presents two peaks, whose binding energy are close to 35.5 and 38 eV, respectively. The two peaks correspond to the W4f5/2 and W4f7/2 states of W⁶⁺ in WO₃, respectively. The corrosion products of elemental W are mainly formed as hydroxides in acidic HCl solution. The acidic HCl solution is more oxidizing and the W oxide shows the highest valence state.

Figure 6

XPS narrow spectrum of Co + 45% WB coating immersed in 0.5 mol·L⁻¹ HCl Solution for 360 h. (a) Co; (b) Fe; (c) Cr; and (d) WO.

4 Conclusion

Cobalt-based composite coatings with gradient concentrations of spherical WB particles were fabricated via laser cladding technology. The electrochemical behavior of these coatings in low-temperature hydrochloric acid environments was systematically evaluated through a series of electrochemical tests, elucidating the electrochemical corrosion mechanisms underlying WB-enhanced cobalt matrix performance. The Co + 15% WB alloy exhibits superior corrosion resistance due to the synergistic oxidation of W and B, forming a dense composite film that inhibits Cl⁻ penetration. The uniformly dispersed WB particles block the diffusion pathways of corrosive media, while grain refinement and interfacial compatibility mitigate the risk of low-temperature brittleness. In contrast, pure Co, with defects in its passive film, and Co + 45%WB, suffering from precipitate agglomeration, fail to achieve this multi-scale synergistic protective mechanism.

The electrochemical polarization and impedance tests of the three coatings in 0.5 mol·L⁻¹ HCl acidic solution showed that the cathodic curve fluctuations of the three coatings were relatively similar, and passivation was produced for Co + 15% WB, Co + 45% WB, and Co coatings. The self-corrosion potential of the coatings was still the largest for Co + 15% WB. It indicates that the surface state of the coating and the content of the hard phase have a greater influence on the corrosion resistance under acidity. The EIS analysis reveals a non-monotonic dependence of corrosion behavior on WB content, as evidenced by the Nyquist and Bode representations. The diameter of the capacitive semicircle, corresponding to the charge transfer resistance, demonstrates a pronounced maximum at 15% WB addition. Specifically, the Co + 15% WB coating exhibits the largest capacitive arc radius among all specimens, indicating optimal corrosion protection performance at this composition. The corrosion current increases in the presence of a larger amount of WB (≥15%), mainly because of the increase in the micropotential difference due to W-rich oxides. In acidic environments, EH40 exhibits heightened susceptibility to corrosion, with the primary mechanism being anodic dissolution.
The three coatings were subjected to room temperature immersion experiments in 0.5 mol·L⁻¹ HCl acidic solution for 360 h to analyze the composition and valence of the corrosion products. The XPS analysis revealed that in the acidic environment, the enhanced oxidizing conditions led to the formation of Co(OH)₂, Co₂O₃, and CoO as the primary compounds on the surface of the Co + 45% WB coatings. Additionally, the oxidation of WB particles resulted mainly in the formation of WO₃, which represents the highest oxidation state of tungsten.

# Lele Han and Li Fan contributed equally to this work and should be considered as co-first authors.

Acknowledgments

The authors gratefully acknowledge the fund support of Shanghai Maritime University and Shanghai Jian Qiao University.

Funding information: This study was financially supported by the Shanghai Engineering Technology Research Center of Deep Offshore Material (19DZ2253100) and the Shanghai Collaborative Innovation Center for Key Steels of Heavy Icebreaker.
Author contributions: Lele Han: writing – original draft, writing – review and editing, methodology, and formal Analysis; Li Fan: writing – original draft, formal analysis, visualization, and project administration; Haiyan Chen: writing – original draft, formal analysis, visualization, and project administration; Guangkuo Zhu: writing – review and editing and methodology; Yujiang Qin: writing – review and editing and methodology; Qizheng Cao: writing – review and editing and methodology.
Conflict of interest: Authors state no conflict of interest.

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Received: 2025-03-17

Revised: 2025-05-11

Accepted: 2025-05-23

Published Online: 2025-07-16

This work is licensed under the Creative Commons Attribution 4.0 International License.

Artikel in diesem Heft

https://doi.org/10.1515/htmp-2025-0082

Schlagwörter für diesen Artikel

laser cladding; tungsten boride; electrochemical corrosion; corrosion resistance; low-temperature environment

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