The Influence of Wire Type on the Properties and Characteristics of Coatings Obtained by the Arc Metallization Method

Abstract

Electric arc spraying is a promising technique for enhancing the wear resistance of components operating under abrasive and mechanical loads, particularly in agricultural soil-processing machinery. This study aims to comparatively analyze the properties of coatings formed using electric arc metallization with cored and solid wires of 30KhGSA and 51KhFA steel grades. Experimental investigations were carried out to evaluate the influence of wire type on the microstructure, microhardness, adhesion strength, and wear resistance of the sprayed coatings. Metallographic analysis and microhardness measurements revealed that coatings produced with cored wire exhibited a finer lamellar structure and higher hardness values compared to those formed with solid wire. Wear tests demonstrated improved resistance under abrasive conditions for cored wire coatings, indicating better performance under operational loads. The optimized spraying parameters were determined to ensure uniform and adherent coatings. The results suggest that using cored wire in electric arc spraying offers significant advantages in forming high-quality protective layers. These findings support the potential application of the developed coatings in extending the service life of soil-engaging machine parts under intensive field conditions.

1. Introduction

Modern industries such as mechanical engineering, aviation, energy, and oil and gas are placing increasingly high demands on the durability, wear resistance, and restoration of parts operating under intense loads and aggressive environments [1,2]. In this context, electric arc metallization (EAM) technology, one of the most effective and versatile methods for forming protective coatings on metal surfaces, is becoming particularly relevant [1].

Electro-arc metallization is a thermal spraying method in which two metal wires are fed into an electric arc zone, melted, and sprayed onto the substrate surface with a jet of compressed air. This method allows for the formation of coatings with high deposition rates, controlled thickness, and reliable adhesion. Its wide technological capabilities, ease of implementation, and low cost make EAM attractive for restoring the geometry of worn parts and increasing their service life.

In recent decades, numerous studies have been devoted to improving the performance of coatings obtained by electric arc metallization. Wielage et al. [2] demonstrated that optimization of spraying parameters and wire composition can significantly reduce porosity and increase adhesion. Boinovich, L.B. et al. [3] investigated the influence of arc spraying factors on coating structure and wear resistance, emphasizing the decisive role of wire type. Gornik et al. [4,5,6] and other researchers showed that variations in spraying distance and wire feed rate directly affect the microstructure and tribological performance of coatings. However, despite these contributions, there is still a lack of systematic research comparing the properties of coatings obtained from cast and cored steel wires, especially under modified spraying conditions [7,8,9,10]. The key factor affecting the quality of the coating obtained is the choice of wire material. Not only the chemical composition, but also the method of wire production (cast or powder) can significantly change the structure, porosity, microhardness, and adhesion of the coating to the substrate. At the same time, the question of the optimal combination of steel grade and wire type for obtaining wear-resistant coatings remains insufficiently studied, particularly in the case of 30KhGSA and 51KhFA steels.

In this regard, the aim of this work is to conduct a comprehensive study of the influence of the type of wire (cast and powder) made from 30KhGSA and 51KhFA steels on the morphological and operational characteristics of coatings obtained by the electric arc metallization method.

2. Materials and Methods

Structural steel 65G, which belongs to the group of spring steels according to GOST 14959–2016, “High-quality structural carbon steels. Technical specifications”, was used as the substrate material. This high-carbon, low-alloy metal is widely used for the manufacture of parts subjected to cyclic loads, such as springs, washers, brake bands, gears, and agricultural machinery parts. The chemical composition of the material is shown in

Table 1. Chemical composition (wt.%) of 65G steel according to GOST 14959–2016.

Fe, %	C, %	Si, %	Mn, %	Ni, %	S, %	P, %	Cr, %	Cu, %
balance	0.62–0.70	0.17–0.37	0.9–1.2	≤0.25	≤0.035	≤0.035	≤0.25	≤0.20

[10].

The substrates were cut from sheet material. Each sample is 4 mm high, 16 mm long, and 10 mm wide. To obtain a homogeneous and smooth surface, the samples were manually sanded using SiC abrasive papers with grit sizes from 100 to 360. The sanding was carried out under uniform hand pressure, with alternating directions between steps to minimize preferential grooves. No mechanical polishing was applied, ensuring identical preparation conditions for all specimens. To obtain the required roughness and improve the adhesion of the coatings to the substrate, sandblasting was performed using electrocorundum with a grit size of 200–250 µm, which ensured uniform surface roughening. Four types of wire were used as the spraying material: cast and flux-cored (powder) wires of grades 30KhGSA and 51KhFA. Their chemical composition is presented in

Table 2. Chemical composition (wt.%) of sprayed wires according to GOST 10543–98 (30KhGSA) and GOST 9389–75 (51KhFA).

Wires	Type	Fe, %	C, %	Si, %	Mn, %	Cr, %	Mo, %
30KhGSA	cast	balance	0.28–0.34	0.9–1.2	0.8–1.1	0.8–1.1	-
30KhGSA	powder	balance	0.28–0.34	0.9–1.2	0.8–1.1	0.8–1.1	-
51KhFA	cast	balance	0.47–0.55	0.15–0.3	0.3–0.6	0.75–1.1	before 0.3
51KhFA	powder	balance	0.47–0.55	0.15–0.3	0.3–0.6	0.75–1.1	before 0.3

, in accordance with GOST 10543-98 (30KhGSA) and GOST 9389-75 (51KhFA). The main parameters of the wires, including type and diameter, are noted in

Table 3. Comparative characteristics of sprayed wires (cast and powder types).

No	Sample Marking	Wire Name	Wire Type	Wire Size, mm	Manufacturing/Structure	Typical Behavior During Spraying	Effect on Coatings
1	W1	30KhGSA	cast	1.6	Drawn from solid billet; dense, homogeneous	Stable melting, smooth feeding	Denser coatings, lower porosity
2	W2	30KhGSA	powder	1.6	Metallic sheath with alloying powder filling	Less stable melting, higher oxidation tendency	Higher hardness, but more porosity
3	W3	51KhFA	cast	1.6	Drawn from solid billet; dense, homogeneous	Stable melting, smooth feeding	Denser coatings, but prone to cracks
4	W4	51KhFA	powder	1.6	Metallic sheath with alloying powder filling	Incomplete fusion possible, oxidation	Higher hardness, more heterogeneity

. The wires were selected based on their high wear resistance, thermal stability, and ability to form dense protective coatings during electric arc spraying. All wires used had the same diameter of 1.6 mm, which provides an optimal balance between stable feed, efficient melting, and uniform spraying, and also allows for easy calibration of the sprayer parameters during comparative experiments [11,12,13,14]. The chemical composition of powder and cast wire grades 30KHGSA and 51KHFA is noted in Table 2.

In addition to their chemical composition, the sprayed wires differ in manufacturing method and structural design. Cast wires are produced by drawing from solid billets, which provides a homogeneous metallic structure and stable melting. Powder wires consist of a metallic sheath filled with alloying powders, which influences melting behavior and may lead to oxide inclusions or pores. The combined characteristics of the wires used in this study are summarized in Table 3.

Coating thickness, porosity, and roughness were determined from at least five measurements at different regions of each sample, while microhardness and adhesion values were based on ten indentations/tests per sample. The values reported in Table 3 are averages of these repeated measurements. The coatings were applied using the supersonic electric arc metallization (EDM) method. The process was carried out using a device that included a power source, a spray gun, and a piston compressor. The essence of the method lies in melting two wires with an electric arc and transferring the molten particles to the prepared surface under the action of compressed air flow [15]. The wires (cast and powder) were fed to the sprayer using a motorized feed system. Melting in the arc zone, the metal was sprayed at high speed and deposited on a 65G steel substrate, forming a protective layer. To ensure the accuracy of the comparative analysis, all spraying was carried out under the same conditions, as shown in

Table 4. Spraying modes for supersonic electric arc metallization.

Parameter	Values
Arc voltage, В	40
Current, А	250
Wire feed speed, cm/s	12
Distance from nozzle to substrate, mm	200
Compressed air pressure, MPa	0.7
Environment temperature, °C	26

.

To obtain reproducible coatings, the optimal spraying mode was selected in advance based on previous preliminary tests. This made it possible to minimize the influence of technological variables and focus on comparing the characteristics of coatings depending on the type of wire [15].

A wide range of methods was used for a comprehensive assessment of the structure and properties of the coatings. The microstructure and morphology of the surface and cross-section were studied using SEM on a MIRA3 microscope (Tescan, Brno, Czech Republic), and the elemental composition was studied using an Xplore 30 EDS system (Oxford Instruments, Abingdon, UK). The porosity and thickness of the coatings were determined using an Olympus BX53M an Xplore 30 EDS system (Oxford Instruments, Abingdon, UK) optical microscope with software processing according to ASTM E2109. Surface roughness (Ra) was measured using a model 130 contact profilometer (tip radius 5 µm) according to ISO 4287. For each sample, five measurements were performed at different locations, and the average Ra value was reported. Microhardness was evaluated using the Vickers method (ISO 6507-1) with a Metlab 502 device (load 0.025 N, exposure 10 s). For each coating, at least ten indentations were made at different areas of the cross-section, the average value was reported, and the microhardness was measured using a FISCHERSCOPE HM2000S (Helmut Fischer GmbH, Sindelfingen, Germany; ASTM E2546) under a load of 245.2 mN and an exposure time of 20 s. The device fundamentally records Martens hardness, but the results were automatically converted by the software into Vickers hardness (HV0.025), which is reported in this study for consistency with previous works and for comparability with the literature. The adhesion of the coatings was tested according to ASTM C633 using an adhesive joint and tensile tests on a device corresponding to ASTM E4. Wear resistance was evaluated based on mass loss before and after testing under abrasive and impact–abrasive conditions in accordance with GOST 23.208-79, including the “rotating roller–flat surface” scheme. The use of uniform spraying modes and standardized sample geometry ensured the comparability of the results, which made it possible to form a reliable experimental basis for analyzing the influence of the type of wire (cast or powder) and steel grade (30KHGSA and 51KHFA) on the formation of the structure and operational characteristics of the coatings [16,17,18].

3. Results and Discussions

The microstructure of coatings obtained by electric arc metallization using 30KHGSA and 51KHFA powder wires was studied using scanning electron microscopy (SEM) at a magnification of ×2000. The results of the microstructural (SEM) and elemental (EDS) analysis showed the significant influence of the wire type and steel grade on the formation of the coating structure. The coatings obtained from 30KHGSA and 51KHFA powder wires are characterized by a relatively uniform distribution of alloying elements and a layered structure typical of electric arc spraying. At the same time, 30KHGSA powder wire formed a denser and more homogeneous structure, while 51KHFA powder demonstrated increased grain size and the highest porosity (4.5%), which is probably due to localized oxidation of individual components. Accordingly, the microhardness of the 30KHGSA coatings was 610 HV, while that of the 51KHFA coatings was 540 HV. Powder coatings also showed satisfactory adhesion and layer thickness values while ensuring effective distribution of the material over the entire substrate area.

A comparison with cast wires revealed that coatings obtained from cast 30KHGSA and 51KHFA have lower porosity (1.6%–3.2%) and a smoother surface but are inferior in hardness (580 and 560 HV, respectively) [15,16]. In addition, EDS analysis indicated the presence of chemical heterogeneity in cast coatings—in particular, areas with local depletion of chromium and silicon were recorded, which correlates with the presence of voids and interlayer defects in SEM images. This indicates uneven material transfer to the arc zone and the instability of spraying. Thus, powder wire, especially 30KHGSA, provides a more balanced combination of density, microstructural integrity, and hardness, while cast 51KHFA demonstrates better performance in terms of porosity and corrosion resistance. These data underscore the importance of considering the method of wire production when selecting the optimal material for EDM coatings.

The SEM images in Figure 1 show that all coatings exhibit a typical lamellar structure, but their density and uniformity strongly depend on the wire type. Powder wire coatings (W2, W4) revealed higher porosity and more pronounced oxidation, while cast wire coatings (W1, W3) displayed a more homogeneous structure, albeit with some interlamellar defects [17].

These differences arise from the fundamental design of the wires. Cast wires, drawn from solid billets, melt uniformly in the arc zone, which promotes stable droplet formation, efficient splat flattening, and the deposition of dense coatings with lower porosity. In contrast, powder wires consist of a metallic sheath filled with alloying powders, where incomplete melting of the core and localized oxidation can occur, leading to heterogeneous lamellae and higher porosity. Such distinctions in melting behavior explain the structural variations observed and their influence on the mechanical performance of the coatings.

In addition, scale bars have been included in all SEM images to provide an accurate dimensional reference. The dark-gray grains observed in some regions, especially in sample W2, are associated with localized segregation of alloying elements with higher atomic numbers, as confirmed by EDS mapping. Such segregation may arise from incomplete mixing of the melt during spraying or from the preferential oxidation of certain components, which leads to the formation of inhomogeneous micro-regions within the lamellar structure. These areas correlate with higher porosity and the presence of oxide inclusions, which may negatively influence coating adhesion and wear resistance.

The EDS maps of the coatings are presented in Figure 2 and Figure 3, while the quantitative elemental composition is summarized in

Table 5. Elemental composition of coatings obtained from 30KhGSA and 51KhFA wires according to EDS analysis.

Element	30KhGSA, wt.%	51KhFA, wt.%
C	8.08 ± 0.10	14.04 ± 0.08
O	–	9.48 ± 0.04
Si	0.64 ± 0.01	1.56 ± 0.01
Cr	0.02 ± 0.01	0.02 ± 0.00
Mn	1.58 ± 0.01	2.03 ± 0.01
Fe	88.94 ± 0.10	72.87 ± 0.08
Ni	0.74 ± 0.01	–
Total	100%	100%

. EDS analysis revealed that both coatings are primarily Fe-based with varying concentrations of C, Si, and Mn. The 30KhGSA coating contained trace Ni, most likely due to background interference or minor contamination during wire manufacturing, while the 51KhFA coating exhibited notable oxygen content (~9.5 wt.%), indicating oxide formation during spraying.

Our observations of lamellar structures and reduced porosity in cast wire coatings are consistent with the results reported by Wielage et al. [18] and Lopata et al. [19], who demonstrated that stable melting of cast wires promotes smoother coatings with lower defect density. At the same time, the denser structure obtained with the 30KhGSA powder wire in our study extends these findings, showing that optimized supersonic arc spraying can achieve comparable or even superior coating density relative to cast wires. The EDS spectra confirm that both coatings are predominantly Fe-based, with carbon, silicon, and manganese detected in varying concentrations (Table 5). It should be noted that the EDS results presented in Table 5 show certain deviations from the nominal chemical composition of 30KhGSA and 51KhFA steels. The abnormally high carbon content is explained by the methodological limitations of EDS: thin oxide and carbide films that form on splat surfaces during arc spraying can lead to an artificial increase in the detected carbon signal. Similar effects were reported in earlier studies of thermally sprayed coatings [20,21,22,23]. The low chromium concentration is associated with its preferential oxidation and segregation into oxide phases, which may remain undetected in localized point analysis [24,25,26,27,28]. The elevated Mn and Si values observed in 51KhFA coatings reflect the formation of Mn- and Si-rich oxides during spraying, which can artificially increase their concentration in the EDS spectrum. These effects are not related to sample misidentification; the results were reproducible in repeated measurements. Therefore, the EDS data should be interpreted primarily as indicators of surface segregation and oxidation phenomena rather than the exact bulk composition of the sprayed wires. In the case of 30KhGSA, only trace amounts of Ni were observed, which can be attributed to background interference or minor contamination during wire manufacturing. For 51KhFA, a significant oxygen peak (~9.5 wt.%) was detected, indicating oxide formation during spraying. These findings are consistent with the darker contrast regions observed in the SEM images, particularly in sample W2, which correlate with localized oxidation processes.

In terms of roughness (Ra), powder wire coatings demonstrate a rougher surface compared to cast counterparts. The lowest roughness was recorded for the 30KhGSA cast (6.5 μm), which is associated with uniform plastic deformation of particles at the moment of deposition [29,30,31]. The greatest coating thickness was observed for the 30KhGSA powder wire (240 μm), whereas the 51KhFA cast wire showed the lowest thickness (190 μm) and the highest porosity (4.5%). This confirms that the wire type significantly affects the density and quality of the sprayed coatings [32,33,34,35].

The highest microhardness was recorded for the 30KhGSA powder coating (610 HV0.025). This result is primarily attributed to microstructural factors rather than carbon content. SEM analysis showed that the 30KhGSA powder coating formed a denser and more homogeneous lamellar structure with finer carbide dispersion and lower porosity compared to other samples. In contrast, the 51KhFA coatings, despite having a higher nominal carbon content, exhibited increased porosity and localized oxidation, which reduced their effective hardness. Thus, the superior hardness of the 30KhGSA powder coating is explained by its structural integrity and defect minimization, rather than by bulk chemical composition alone. Although 51KhFA steel contains more carbon, the coatings obtained from 30KhGSA demonstrated higher hardness due to microstructural factors rather than bulk composition. SEM analysis showed that 30KhGSA coatings form a denser and more homogeneous lamellar structure with finer carbide dispersion, while 51KhFA coatings revealed higher porosity and localized oxidation. These structural defects reduce the effective strengthening in 51KhFA coatings, whereas the integrity and uniformity of 30KhGSA layers promote higher hardness. Thus, the difference in hardness arises mainly from structural integrity and defect density, which outweigh the influence of nominal carbon content and alloying elements [36]. Cast wires demonstrate lower hardness values on average, but they are superior in terms of uniformity and lower porosity.

Adhesion values were highest for the 30KHGSA cast wire coating (40 MPa), while the 51KHFA powder coating showed the lowest adhesion (28 MPa). This may be due to oxide inclusions and increased porosity in the interface zone with the substrate. A similar trend can be seen in the analysis of abrasive wear: 30KHGSA coatings (especially cast type) proved to be the most resistant, while powder 51KHFA showed the greatest loss of mass (19.6 mg). This confirms the denser structure and better particle distribution of coatings applied with cast wires. Although porosity is often considered a key factor influencing adhesion, our results indicate that adhesion strength did not follow a straightforward inverse trend with average porosity values (

Table 6. Comparative characteristics of coatings.

Sample	Thickness (μm)	Porosity (%)	Ra (μm)	HV0.025	Adhesion (MPa)	Wear (mg)
W1	210	2.1	7.2	610	36	14.2
W2	240	1.6	6.5	580	40	12.8
W3	190	4.5	9.1	540	28	19.6
W4	225	3.2	8.3	560	33	16.4

, Figure 3). This behavior is attributed to the non-uniform distribution of pores and the dominant role of the coating–substrate interface. In particular, the 30KhGSA powder coating, despite not having the lowest porosity, demonstrated the highest adhesion (40 MPa) because of a dense interfacial layer and uniform lamellar bonding. By contrast, the 51KhFA cast coating exhibited lower adhesion due to oxide inclusions and interlamellar defects near the interface. These findings suggest that adhesion in arc-sprayed coatings is governed more by interfacial quality and defect distribution than by the average porosity level.

The comparative histograms of coating characteristics are shown in Figure 4. The data are consistent with the values summarized in Table 5, which ensures the reliability of the analysis. The 30KhGSA powder coating (W2) exhibited the greatest thickness (240 µm) and high microhardness (580 HV0.025), while the 51KhFA cast coating (W3) had the lowest thickness (190 µm) and the highest porosity (4.5%). Adhesion values were the highest for W2 (40 MPa) and lowest for W3 (28 MPa), confirming that both steel grade and wire type significantly influence coating density, hardness, and bonding strength.

The corrosion resistance of the coatings was evaluated using the potentiodynamic polarization method in a 3.5% aqueous NaCl solution [37]. The main parameters used were corrosion current density, Icorr; corrosion potential, Ecorr; and the calculated corrosion rate, Vcorr (

Table 7. Corrosion current density Icorr (µA/cm²).

Samples	Corrosion Current Icorr, (µA/cm2)	Free Corrosion Potential Ecorr, (mV)	Corrosion Rate, Vcorr, mm/year
30KhGSA Bare substrate	0.36671	−412	0.085
W1	0.23833	−423	0.055
W2	0.26588	−439	0.062
50KhFA Bare substrate	0.39669	−408	0.091
W3	0.21395	−418	0.050
W4	0.24839	−430	0.058

). The value of Icorr reflects the intensity of electrochemical degradation: the lower the current, the higher the resistance to corrosion. Ecorr characterizes the material’s tendency toward spontaneous corrosion, while Vcorr directly determines the actual rate of degradation in an aggressive environment. The results of corrosion tests for various samples, including base steels and coatings W1-W4, are presented in Figure 4. The obtained data indicate a significant improvement in the corrosion resistance of the coatings compared to the base materials, especially in the cases of 30KhGSA and 51KhFA wires

The improved corrosion resistance of 51KhFA coatings, indicated by the lowest Icorr and highest Ecorr, is consistent with the observations of Ndumia et al. [38,39] and Rakhadilov et al. [40,41], where reduced corrosion current densities were associated with the formation of stable passive films. Compared to these works, our results showed slightly higher Ecorr values, which can be explained by the effect of supersonic arc spraying, leading to denser coatings with improved adhesion and reduced pathways for electrolyte penetration.

4. Conclusions

In the present study, a comprehensive comparative analysis was conducted on coatings formed by arc spraying using powder and cast wires made of 30KhGSA and 51KhFA steels. The investigation included morphology, elemental composition, microhardness, roughness, porosity, adhesion, wear resistance, and corrosion resistance, leading to the following findings:

• Coatings produced with powder wires demonstrated higher structural repeatability, technological stability, and efficient deposition of sprayed material, particularly when using 30KhGSA steel.
• Cast wires exhibited superior adhesion to the substrate and the lowest corrosion current density (Icorr), indicating effective surface passivation-especially in the case of the 51KhFA coating.
• According to EDS analysis, the observed differences in oxide and alloying element content correlated with the porosity of the coatings, suggesting the significant influence of oxidation processes on microstructure formation.
• The 30KhGSA powder wire provided the best combination of wear resistance, microhardness, and uniform particle distribution at relatively low surface roughness, making it preferable for applications involving abrasive loads.
• The 51KhFA cast wire demonstrated the highest corrosion resistance along with acceptable mechanical properties, allowing it to be recommended for service in aggressive environments.

Thus, the optimal choice of wire material for arc spraying should be based on the primary performance requirements: for systems exposed to abrasive wear, 30KhGSA powder wire is advisable; for corrosive environments, 51KhFA cast wire is more suitable.