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Article

Effect of Welding Current on the Dilution and Mechanical Properties of Co–Cr Alloy Stellite-6 Coatings Applied to AISI 4130 Steel

by
Elias Rocha Gonçalves Júnior
1,*,
Bárbara Ferreira de Oliveira
1,
Luis Augusto Hernandez Terrones
1,
Noan Tonini Simonassi
1 and
Sergio Neves Monteiro
2
1
Advanced Materials Laboratory, State University of Northern Rio de Janeiro Darcy Ribeiro-UENF, 2000 Alberto Lamego Avenue, Campos dos Goytacazes 28013-602, Brazil
2
Section of Mechanical Engineering and Material, Military Engineering Institute-IME, 80 Gen. Tibúrcio Square, Rio de Janeiro 22290-270, Brazil
*
Author to whom correspondence should be addressed.
Coatings 2024, 14(12), 1591; https://doi.org/10.3390/coatings14121591
Submission received: 24 November 2024 / Revised: 17 December 2024 / Accepted: 18 December 2024 / Published: 19 December 2024
(This article belongs to the Special Issue Microstructure, Friction and Wear, Hardness Properties and Numerical Simulation of Coatings)
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Abstract

:
Coating welding with cobalt alloys on pipelines is crucial for the offshore industry due to its exceptional resistance to corrosion and wear. In this paper, two welding conditions with different currents were proposed to observe the behavior of the dissimilar joint. The microstructure, mechanical properties, and dilution of a dissimilar material consisting of AISI 4130 steel substrate coated with Stellite 6 alloy were analyzed. Firstly, samples were metallographically prepared for the evaluation of the weld bead and the coating phases using SEM, EDS, and XRD analyses. Then, microstructural characterization was performed qualitatively using confocal microscopy and quantitatively to determine the phase fraction volumes in the dendritic and interdendritic regions, as well as the resulting dilution. Results revealed that varying welding conditions did not significantly affect the hardness of the coatings, which remained within the alloy standard of 36-45 HRC, with microhardness varying by 3%–5% from one condition to another and phase fraction volume showing a variation of 5.6% between welding conditions. On the other hand, experimental results indicated a clear effect of welding current variation on dilution values, with 4.6% for condition 1 and 16.7% for condition 2, allowing for direct proportional relationships to be established, i.e., higher deposition current results in greater dilution.

1. Introduction

Dissimilar materials can be described as materials or combinations of materials that are difficult to bond, either due to their individual chemical compositions or significant differences in physical properties between the two materials being joined [1,2,3]. There are various processes that can be used for protecting and creating surfaces with special characteristics from these types of materials, such as the plasma transferred arc (PTA) coating deposition technique. In this technique, the filler material is in the form of atomized powder of the alloy of interest with controlled particle size [4,5], along with greater control over the formed microstructure and improved homogeneity of the properties of the obtained deposits [6].
The use of dissimilar coatings can mitigate the effects of external agents in industrial materials by employing special alloys designed for this purpose, known as superalloys. The main characteristics of superalloys include superior tribological properties along with excellent mechanical resistance [7,8]. Among these superalloys, cobalt-based superalloys stand out, as they are generally described as resistant to wear, corrosion, and high temperatures [9,10].
The application of dissimilar coatings, such as Stellite 6, deposited through the PTA process, must be conducted with parameter control, as these parameters directly influence the dilution of the coating [2,11,12,13], the quality of the weld, and other aspects resulting from the process, such as the volume fraction of carbides, hardness, and metallurgical properties [14,15,16,17].
In this paper, microstructure and substructure, mechanical properties through hardness and microhardness tests, and the dilution of a dissimilar material consisting of AISI 4130 steel substrate coated with Stellite 6 alloy were analyzed. Additionally, the mechanical properties were analyzed through hardness and microhardness. Two welding conditions with different currents were proposed to observe the behavior of the dissimilar joints under different conditions.

2. Materials and Methods

Two AISI 4130 steel billets were used, each with a length of 200 mm and internal and external diameters of 81.6 mm and 101.6 mm, respectively. These billets were coated with Stellite 6 alloy powder using the plasma transferred arc (PTA) welding process. The chemical compositions of AISI 4130 steel and Stellite 6, provided by the Alphatec company, located in Macaé/RJ, Brazil, are presented in Table 1.
Initially, one of the AISI 4130 steel billets was coated with Stellite 6 alloy using the PTA welding process with parameters and conditions previously used by the company. The other billet was coated using a different welding current, as described in Table 2.
For microstructural analysis, a sample was sectioned from the tubes in both conditions and prepared metallographically following these steps: grinding with abrasive papers ranging from 100 to 1200 grit; polishing with 1 μm and 0.3 μm alumina paste on adhesive abrasive cloth suitable for each paste used. The chemical etching was performed in two stages with different solutions due to the presence of two dissimilar materials in the analyzed samples.
To reveal the microstructure of the AISI 4130 steel, as well as the morphology of the phases present and impurities, etching was performed by immersion with a 2% Nital solution for 55 s. For the Stellite 6 coating, etching was done by immersion using Murakami’s solution (10 g of potassium ferricyanide + 10 g of sodium hydroxide in 100 mL of water) for 20 s.
For obtaining micrographs of the previously etched samples, the OLYMPUS LEXT OLS 4000 confocal microscope (OLYMPUS, Tokyo, Japan) and the Zeiss EVO MA10 scanning electron microscope (SEM, ZEISS, Oberkochen, Germany) were used, along with microanalysis through energy-dispersive X-ray spectroscopy (EDS, ZEISS, Oberkochen, Germany) utilizing a spectrometer coupled to the SEM.
X-ray diffraction (XRD) was used to identify the phases formed in the coating under both welding conditions. For this purpose, a Bruker D8 ADVANCE diffractometer (Bruker, Bremen, Germany) was employed.
In addition to determining the microstructure present in the samples, 15 micrographs obtained from the confocal microscope at a magnification of ×1075 were used for the quantitative analysis of secondary dendritic spacings in the samples. In these structures, secondary dendritic arm spacing is the most common parameter used for characterizing the refinement of the microstructure. Among the methods proposed by Vandersluis and Ravindra [18], method D was selected because it enhances precision by focusing on center-to-center distances between secondary arms, effectively minimizing errors from dendrite asymmetry.
Thus, micrographs of fifteen distinct regions of the samples were obtained. In each region, a straight line of length L was drawn along the primary dendrite arm, and the number of secondary dendrite arms N that crossed these lines was counted with the help of ImageJ software (version IJ 1.46r). The secondary dendrite arm spacing (SDAS) was then calculated using Equation (1).
SDAS = L/(N − 1)
To measure dilution (Equation (2)), metallographic preparation of the samples was required, following steps of grinding and polishing. The measurements of the reinforcement areas A and the penetration areas B of each weld bead were obtained using ImageJ software.
D (%) = (B/(A + B)) × 100
To determine the volume fraction of the phases present in the samples, the ASTM E562-11 standard [19] was used. The point grid can be employed in two configurations: circular and square, with the latter being used in this paper [20]. The calculation for quantifying the phases of interest was performed using Equation (3), which considers the volume fraction percentage of the phase (Pf), the number of intersection points (Pi), and the total number of points (Nt). For this purpose, 15 micrographs obtained with the confocal microscope at various magnifications were used.
Pf = (Pi/Nt) × 100
To calculate the dilution, metallographic preparation of the samples was essential, involving steps such as grinding and polishing. The dilution was determined based on Equation (4) [17,21].
D (%) = ((Fecoating − Fepowder)/Fesubstrate) × 100
where Fecoating is the weight percentage of Fe in the coating, Fepowder is the weight percentage of Fe in the atomized powder Stellite 6; and Fesubstrate is the weight percentage of Fe in the substrate. The Fe content in the coating and the steel substrate was obtained through EDS analysis using the energy-dispersive X-ray spectroscopy (EDS) system coupled with the Zeiss EVO MA10 scanning electron microscope (SEM). The Fe content in the atomized Stellite 6 powder is listed in Section 3.
Rockwell C hardness tests [22] were conducted using an analog bench hardness tester WPMA, with a load of 150 kgf (1471 N) following a preload of 20 kgf (196.1 N). The average hardness value and the corresponding standard deviation for each sample were obtained after five measurements, with the positions being randomly distributed across the sample.
The Vickers microhardness profile along the coating was determined using the Shimadzu HMV-2 microhardness tester, with a load of 500 gf and a loading time of 15 s, for both proposed conditions. The average and standard deviation of the measurements were obtained from 10 indentations, with measurements taken approximately every 100 µm.

3. Results and Discussions

3.1. Optical Microscopy

3.1.1. Condition 1

Figure 1 shows micrographs of the interface between the Stellite 6 coating and the SAE 4130 steel at different magnifications. It can be observed that the formation of dendrites exhibits a predominantly cellular orientation near the weld interface (Figure 1a), suggesting the possible existence of a partially diluted zone (PDZ) (Figure 1b).
The solidification structure of the alloy composing the coating, as well as the change in the solidification path, can be observed in Figure 1a. This is attributed to a potential change in composition due to the gradient of dilution as it moves away from the melt pool and variations in cooling rates, which account for the differences in the thickness of the PDZs [15,23,24,25].
The microstructure consists of solid solution dendrites of Co (light phase) (FCC structure) and interdendritic regions formed from the Co and Cr eutectic with carbides (HCP structure). The lighter regions represent the solid solution of Co (dendrites), while the darker phases correspond to the segregation of carbides that formed due to precipitation during solidification. This same microstructure is observed by other authors [26,27,28].
In the case of the substrate, the microstructure of hypoeutectoid steel is presented, where the light regions are composed of ferrite and the dark regions are composed of pearlite, as indicated in the literature [29]. The heat-affected zone (HAZ), which was influenced by the thermal cycles of welding, may exhibit an increase in grain size. It is well-known that the characteristics of the HAZ depend on the type of substrate and the welding process [30,31,32].

3.1.2. Condition 2

In the micrograph presented in Figure 2, the microstructure around the interface of the Stellite 6 coating on SAE 4130 steel is shown, consisting of solid-solution dendrites of Co (FCC structure) and interdendrites formed from Co and Cr eutectic with carbides, similar to condition 1. It can also be inferred that the formation of the dendrites follows a predominantly planar–columnar orientation (Figure 2b) characterizing a coarser microstructure [33,34,35,36].
The solidification structure of the alloy that makes up the coating can be observed, as well as the change in the solidification path, as shown in Figure 2a. Figure 2c presents a higher magnification micrograph of the interface between the substrate and the coating alloy, highlighting the formation of a PDZ (partial dilution zone). According to Silva et al. [23], this forms when the liquid substrate is driven into the weld pool, creating regions of random orientations.
The PDZ presented in Figure 2c can be classified as a beach-type structure [33], as it is characterized by thin, narrow bands along the fusion line. Beach-type structures are discontinuous, sometimes covering internal or external parts of the fusion line, varying in thickness, and are described as typical transition zones. Similar to sample 1, a hypoeutectoid steel microstructure can be observed, where the light regions are composed of ferrite and the dark regions are composed of pearlite.
The characteristics of the HAZ in the weld depend on the effects of the welding thermal cycle. In the case of the base metal under the second welding condition, the microstructure suggests the potential formation of distinct regions, such as the coarse-grained zone and the fine-grained zone [30,37,38], likely associated with the effects of high temperatures and rapid cooling during the process.

3.2. Scanning Electron Microscopy with Energy Dispersive X-Ray Spectroscopy (SEM/EDS)

Figure 3 shows two micrographs of the coating microstructure, with several points analyzed by EDS indicated for condition 1 (Figure 3a) and condition 2 (Figure 3b). Some of the points located in the regions of interest of the samples have been selected.
Points 367 and 368, corresponding to the dendritic region, are rich in Co with high concentrations of Cr and C due to their proximity to an interdendritic region rich in these elements, while points 369 and 380 correspond to the interdendritic region. These points can be observed in Figure 3a.
The data obtained from these four points were compiled and summarized in Table 3 to compare the concentration of elements through their average and their dispersion across the sample based on the standard deviation. The analysis of the standard deviation values for each element indicates a high variation in the concentrations of Co, Cr, and C—elements characteristic of the interdendritic region—which may suggest the formation of different types of carbides in this phase of the coating [39,40].
Figure 4 shows the micrograph obtained by SEM and the line EDS analysis performed in condition 1 to evaluate the behavior of element content, including the substrate, the PDZ, and the Stellite 6 coating layer.
It is observed that the elements identified in the BM region were Fe and Cr, with C, Co, and Mo present in smaller amounts. This chemical composition was expected for the SAE 4130 steel tube.
From the fusion line, a high Fe content is observed, which decreases sharply. This behavior aligns with the appearance of the PDZ region. Conversely, there is an increase in Cr and Co content, which fluctuates as one moves away from the coating surface toward the PDZ.
Points 352 and 354 are located in a dendritic region of the coating microstructure for condition 2, which is rich in cobalt and shows significant concentrations of Cr and C, along with an atypical concentration of Fe for the studied alloy. Points 364 and 365 are situated in an interdendritic region within the microstructure of this coating. These points can be observed in Figure 3b.
As with the data from the selected points for condition 1, the data for the points corresponding to condition 2 were compiled and summarized in Table 4, following the same evaluation of element concentration and dispersion parameters.
Figure 5 shows the EDS line analysis of condition 2. In contrast to what was observed in condition 1, from the fusion line, a high Fe content is observed to decrease; however, it remains at levels reasonably higher than what would be typical for the deposited alloy, in this case, Stellite 6.
A significant point to highlight is the above-average concentration of Fe in the coating, compared to the values listed in Table 1, which provides the chemical components and their respective percentages in the original alloy. Table 4 presents data for the dendritic region of condition 1 sample, showing an average of 2.48% Fe, while Table 5 shows an average of 14.25% Fe in the coating of condition 2.
This Fe content may be related to the dilution of the base metal during the coating process, which, in addition to altering the solidification structure, could modify the composition of the precipitates, leading to the formation of fragile microstructures that are susceptible to corrosion [41].
When comparing the data obtained from the interdendritic regions of the coatings in samples 1 and 2, a disparity in iron composition is observed. This discrepancy was also noted and reported previously for the dendritic region of condition 2. For condition 1, the average Fe concentration is 1.9%, while sample 2 shows an average value of 11.5%.

3.3. X-Ray Diffraction (XRD)

XRD analysis was conducted to identify the phases present in the coatings and any possible oxides formed. Figure 6 presents the XRD patterns for the polished surfaces of the coatings from samples under conditions 1 and 2.
For the coating in condition 1 (Figure 6a), the presence of Cr7C3 and Cr23C6 carbides was identified. In these alloys, it is common to form carbides such as M6C, M7C3, and M23C6, with the M23C6 carbide playing a significant role in mechanical strength by inhibiting dislocation movement [39]. The observed carbides tend to form at grain boundaries in the form of coarse particles and are characterized as a structure of hard particles [42].
For the coating in condition 2 (Figure 6b), carbides of Cr7C3, Cr23C6, WC, and Fe3C types were observed. WC carbides, also noted by Antoszczyszyn et al. [43], are formed shortly after solidification and are distributed heterogeneously throughout the dendrites. Additionally, variations in welding current can alter the final composition, as seen in studies on Co-based alloys, where welding parameters significantly impact carbide formation and phase stability [44].
The absence of Fe₃C and WC in condition 1 is likely due to differences in dilution behavior and cooling rates between conditions [37]. When carbide-forming alloying elements are present, and the base metal is rich in Fe, the formation of cementite (Fe3C) in the coating can occur, depending on the diffusion of interstitial carbon and the observed dilution rate [11,45].

3.4. Secondary Dendritic Spacing (SDS), Dilution and Phase Quantification

The primary arm spacings, measured using Method D, which is considered the most accurate among the five methods for both fine and coarse microstructures [18], were chosen randomly. This indicated an average SDS of 4.21 ± 0.63 μm for condition 1 and an average of 4.45 ± 0.70 μm for condition 2. Based on the average SDS, it can be stated that no significant variation was observed in the final microstructure between welding condition 1 and condition 2, with both conditions resulting in comparable microstructural characteristics [46].
Antoszczyszyn et al. [43] noted a growing linear relationship between the deposition current and substrate dilution, considering a constant volume feed rate, as in this study. The optimal current value should be as low as possible while resulting in the maximum powder melting rate and proper deposition for a given feed rate [47].
Since the deposition current directly affects dilution, it was determined (Equation (4)) to assist in analyzing the influence of deposition current and substrate on the characteristics and properties of the obtained coatings (Table 5).
The dilution, calculated using Equation (2), reached 4.6% for condition 1 and 16.7% for condition 2, indicating a directly proportional increase in this indicator with the rise in deposition current. The dilution value found for the coating deposited under welding condition 2 (16.7%) is above the typical dilution range for the PTA process, which is 4% to 10% [6], indicating that the current intensity was likely too high for optimal alloy deposition. Such elevated dilution can negatively affect key properties, potentially diminishing the coating’s corrosion, mechanical, and erosion resistance by introducing more substrate material and reducing alloy concentration in the coating [48,49]. For coatings aimed at durability, a lower dilution within the standard range generally supports better performance by maintaining the intended alloy characteristics [2,11,12,13].
As observed, there is a correlation between dilution and the main arc current, indicating a direct relationship between these two variables. That is, a higher current results in greater dilution in the weld bead [50].
The variation in welding current across different conditions can potentially influence the formation of residual stress within coating welds, with higher currents having the capacity to induce more pronounced stress levels [1]. Higher welding currents increase heat input, which can lead to greater thermal gradients as the weld cools, and this variation in cooling and contraction may introduce residual stress across the coating as certain areas solidify at different rates [11,43].
Furthermore, the slower cooling rates associated with higher welding currents may contribute to the accumulation of residual stress in coating welds [21]. Under high-current conditions, the gradual cooling process could allow internal stresses to build up as the coating contracts unevenly on the substrate [47]. This accumulated stress may impact the coating’s durability, potentially affecting its resistance to environmental exposure, corrosion, and mechanical wear [42].
Regarding the volumetric quantification of the phases present in the coating, solid-solution Co dendrites and interdendrites formed from Co and Cr eutectic with carbides were analyzed using Equation (3). The results for the two welding conditions indicated an average volumetric fraction of 29.9% of hard carbide phases (interdendritic region) for condition 1, while condition 2 showed an average fraction of 24.3% for this same phase. These results are presented in Figure 7.
The variation in current intensity did not significantly influence the volumes of the phases—dendritic and interdendritic regions—in both coatings. Therefore, it cannot be concluded that a more refined microstructure was formed when comparing the two proposed welding conditions, as there is only a 5.6% variation in the volumetric fraction between them.
Paes et al. [51] observed that the variation in the fraction of carbides in coatings can reach levels close to 45%, depending on the range of current applied during the welding process, which is expected to have a differentiated impact on the coating properties.
Antony [52] presented a quantitative analysis of the microstructure of Stellite 6 alloy, indicating that the volume fraction of this phase tends to affect mechanical properties, as these are strongly dependent on the presence of carbides and the formed microstructure [26,28,39,53].

3.5. Hardness and Microhardness

A load of 150 kgf (1471 N) was applied to assess the hardness along the coating for both welding conditions. Table 6 presents the values obtained from five indentations, the average of these values, and the standard deviation.
The indentations performed on the samples yielded average hardness values of 44 ± 4 HRC for condition 1 and 36 ± 2 HRC for condition 2. These results are within the hardness range indicated for the original alloy, which is 36-45 HRC [54].
The observed difference in hardness between the two conditions can be attributed to the dilution levels and specific elemental changes within the coating. In condition 1, the lower dilution level (4.6%) results in higher hardness, while in condition 2, the increased dilution (16.7%) introduces a significantly higher amount of Fe from the base material into the coating. Higher dilution rates, such as in condition 2, introduce more base material into the coating, with Fe being the only significant element. This increase in Fe dilutes the concentration of wear-resistant alloy elements, thereby reducing hardness across the coating’s thickness. These findings align with established results in the literature [44,55].
The hardness values of a coating are directly related to its microstructure and chemical composition, providing an initial assessment of the variation in properties, which are dependent on the welding process parameters [56]. Therefore, lower dilution levels help retain the original alloy properties, resulting in consistent hardness throughout the coating and enhancing its mechanical durability [49,57]. This allows for an indirect evaluation of the influence of dilution on these properties [2,11,12,13,53].
Microhardness profiles along the deposited layers using the two sets of welding parameters were obtained with an HV0.5 load and are presented in Figure 8. The average microhardness value along the deposited layer for condition 1 (C1) was 643 ± 23 HV. The transition between the deposited layer and the substrate begins around 0.7 mm from the surface, with the substrate showing an average microhardness of 291 ± 6 HV. For condition 2 (C2), the average value along the coating was 608 ± 18 HV, while the substrate had a microhardness of 281 ± 11 HV. Similar to condition 1, the transition between the deposited layer and the substrate starts approximately 0.7 mm from the surface.
Analyzing the obtained data, it can be stated that the variation in current intensity for conditions 1 (90A) and 2 (109A) did not markedly influence the hardness and microhardness values in the analyzed samples. The primary factor influencing the variation in microhardness between the dissimilar joint materials is the difference in chemical composition between the coatings and the substrate, with a higher amount of carbides present in the coatings. Additionally, the greater refinement found in the microstructures of these coatings, resulting from the high solidification rates associated with the PTA process, contributes to higher hardness compared to the values of the AISI 4130 steel substrate.
It can be observed that there is no significant variation in microhardness values along the coating in both cases, indicating probable uniformity in the distribution of carbides responsible for increasing the material’s hardness [58] and in the microstructure of the sample.
Paes and Scheid [11] mapped the effect of dilution on the hardness of the same alloy and found that increased dilution results in lower hardness, even though the variations are modest. This is evident in the case of condition 2, which has higher dilution compared to the hardness values obtained in condition 1 with lower dilution.

4. Conclusions

It was observed that different welding conditions led to distinct microstructural formations in the coatings, even though both are composed of solid-solution Co dendrites and interdendrites formed from the Co and Cr eutectic with carbides, which formed due to precipitation during solidification.
In condition 1, a columnar dendritic structure is observed, and cellular dendritic structures are present throughout the coating layer. Additionally, a partially diluted zone of the peninsula and bay type is formed, characterized by areas of lack of fusion. In contrast, condition 2 shows that the dendrites form with a predominantly planar–columnar orientation, resulting in a coarser microstructure, including the formation of a partially diluted zone with a beach-like structure characterized by fine and narrow bands along the fusion line.
The results indicate that the proposed welding conditions achieved coating hardness within the ideal range of 36-45 HRC, with condition 1 reaching 44 HRC and condition 2 achieving 36 HRC. These conditions led to slight variations in hardness across different regions of the material, suggesting subtle differences in hardness distribution that could impact localized wear resistance. Additionally, differences in phase fraction volume were observed between the two welding conditions, reflecting shifts in the microstructural composition of the coatings. Although these variations are relatively minor, they demonstrate the sensitivity of the coating’s mechanical performance to changes in welding parameters, which can influence its durability and overall effectiveness in practical applications. The coating from condition 1, with a lower level of dilution, showed a higher fraction of carbides compared to the values obtained in condition 2.
On the other hand, experimental results indicated a clear effect of welding current variation on dilution values, with 4.6% for condition 1 and 16.7% for condition 2, allowing for direct proportional relationships to be established.
This paper highlights how welding parameters influence the microstructural evolution of coatings, specifically how variations in welding current impact phase distribution and dilution levels. The investigation demonstrated that altering welding conditions results in distinct microstructures, affecting the fraction of carbides and overall dilution. The research establishes a clear link between welding current and dilution, providing valuable insights for optimizing welding processes to enhance coating performance and material properties. This contribution is crucial for refining industrial applications where precise control over microstructure and composition is essential.

Author Contributions

Conceptualization, E.R.G.J., B.F.d.O. and L.A.H.T.; methodology, E.R.G.J., B.F.d.O. and L.A.H.T.; software, E.R.G.J.; validation, E.R.G.J.; formal analysis, E.R.G.J., B.F.d.O. and L.A.H.T.; investigation, E.R.G.J., B.F.d.O. and L.A.H.T.; resources, E.R.G.J., B.F.d.O., L.A.H.T. and S.N.M.; data curation, E.R.G.J.; writing—original draft preparation, E.R.G.J. and N.T.S.; writing—review and editing, E.R.G.J. and N.T.S.; visualization, E.R.G.J.; supervision, E.R.G.J., B.F.d.O. and L.A.H.T.; project administration, E.R.G.J. and L.A.H.T.; funding acquisition, L.A.H.T. and S.N.M. All authors have read and agreed to the published version of the manuscript.

Funding

This research was funded by CAPES, CNPq, and FAPERJ—E-26/200.669/2022.

Institutional Review Board Statement

Not applicable.

Informed Consent Statement

Not applicable.

Data Availability Statement

Data are contained within the article.

Acknowledgments

The authors thank FAPERJ, CAPES, and CNPq for financial support.

Conflicts of Interest

The authors declare no conflicts of interest. The authors have no financial or proprietary interests in any material discussed in this article. This article is derived from the Master’s thesis of E.R.G.J., which was presented in 2019 at the Science and Technology Center, part of the Advanced Materials Laboratory, State University of Northern Rio de Janeiro Darcy Ribeiro—UENF. There are no conflicts of interest between the preprint of this thesis and this article.

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Coatings 14 01591 g001
Figure 1. Micrographs of the substrate and coating interface showing the formation of peninsula-type PDZ: (a) magnification: 200×; (b) magnification: 500×.
Figure 1. Micrographs of the substrate and coating interface showing the formation of peninsula-type PDZ: (a) magnification: 200×; (b) magnification: 500×.
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Coatings 14 01591 g002
Figure 2. Micrographs of the substrate and coating interface: (a) magnification: 200×; (b) magnification: 200×; (c) magnification: 500×.
Figure 2. Micrographs of the substrate and coating interface: (a) magnification: 200×; (b) magnification: 200×; (c) magnification: 500×.
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Coatings 14 01591 g003
Figure 3. Scanning electron micrographs highlighting the EDS analysis points: (a) condition 1; (b) condition 2.
Figure 3. Scanning electron micrographs highlighting the EDS analysis points: (a) condition 1; (b) condition 2.
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Figure 4. EDS line scan analysis at the substrate/coating interface for condition 1.
Figure 4. EDS line scan analysis at the substrate/coating interface for condition 1.
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Figure 5. EDS line scan analysis at the substrate/coating interface for condition 2.
Figure 5. EDS line scan analysis at the substrate/coating interface for condition 2.
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Figure 6. XRD analysis for Stellite 6 coatings: (a) condition 1; (b) condition 2.
Figure 6. XRD analysis for Stellite 6 coatings: (a) condition 1; (b) condition 2.
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Figure 7. Average volume fraction of phases in the coating for the two proposed welding conditions.
Figure 7. Average volume fraction of phases in the coating for the two proposed welding conditions.
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Figure 8. Hardness test results along the coating for both welding conditions. Load = HV0.5.
Figure 8. Hardness test results along the coating for both welding conditions. Load = HV0.5.
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Table 1. Chemical composition (%) of the materials used.
Table 1. Chemical composition (%) of the materials used.
MaterialCNiCrMoWMnSiPSFeCo
AISI 41300.300.500.800.15-0.600.150.040.04Bal. 1-
Stellite 61.003.0029.001.504.501.001.50--3.00Bal. 1
1 Bal.: balance—the amount of the base element adjusted to complete 100% of the composition.
Table 2. Welding parameters.
Table 2. Welding parameters.
Welding ConditionCurrent (A)Layer Thickness (mm)Granulometry (μm)
190253–180
2109253–180
Table 3. Concentration of chemical elements at EDS analysis points for coating condition 1.
Table 3. Concentration of chemical elements at EDS analysis points for coating condition 1.
ElementPointAverage
367368369380
Co (%)60.1060.4061.1060.3060.48 ± 0.43
Cr (%)23.2023.1023.0022.8023.03 ± 0.17
C (%)9.609.309.2010.009.53 ± 0.36
W (%)3.102.602.402.902.75 ± 0.31
Fe (%)2.302.702.502.402.48 ± 0.17
Si (%)1.201.401.301.401.33 ± 0.10
Mo (%)0.400.400.400.300.38 ± 0.05
Table 4. Concentration of chemical elements at EDS analysis points for coating condition 2.
Table 4. Concentration of chemical elements at EDS analysis points for coating condition 2.
ElementPointAverage
352354359360
Co (%)52.3052.3052.3052.4052.33 ± 0.05
Cr (%)21.0020.9021.0020.9020.95 ± 0.06
Fe (%)14.0014.4014.3014.3014.25 ± 0.17
C (%)8.508.407.808.108.20 ± 0.32
W (%)2.502.502.602.802.60 ± 0.14
Si (%)1.201.101.401.201.23 ± 0.13
Mo (%)0.500.400.500.400.45 ± 0.06
Table 5. Dilution results for coatings under each proposed condition.
Table 5. Dilution results for coatings under each proposed condition.
Welding ConditionDilution (%)
14.6
216.7
Table 6. Hardness test results along the coating for both welding conditions. Load = 150 kgf (1471 N).
Table 6. Hardness test results along the coating for both welding conditions. Load = 150 kgf (1471 N).
Welding ConditionHardness (HRC)Average
14542394844844 ± 4
2353435363836 ± 2
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Gonçalves Júnior, E.R.; de Oliveira, B.F.; Terrones, L.A.H.; Simonassi, N.T.; Monteiro, S.N. Effect of Welding Current on the Dilution and Mechanical Properties of Co–Cr Alloy Stellite-6 Coatings Applied to AISI 4130 Steel. Coatings 2024, 14, 1591. https://doi.org/10.3390/coatings14121591

AMA Style

Gonçalves Júnior ER, de Oliveira BF, Terrones LAH, Simonassi NT, Monteiro SN. Effect of Welding Current on the Dilution and Mechanical Properties of Co–Cr Alloy Stellite-6 Coatings Applied to AISI 4130 Steel. Coatings. 2024; 14(12):1591. https://doi.org/10.3390/coatings14121591

Chicago/Turabian Style

Gonçalves Júnior, Elias Rocha, Bárbara Ferreira de Oliveira, Luis Augusto Hernandez Terrones, Noan Tonini Simonassi, and Sergio Neves Monteiro. 2024. "Effect of Welding Current on the Dilution and Mechanical Properties of Co–Cr Alloy Stellite-6 Coatings Applied to AISI 4130 Steel" Coatings 14, no. 12: 1591. https://doi.org/10.3390/coatings14121591

APA Style

Gonçalves Júnior, E. R., de Oliveira, B. F., Terrones, L. A. H., Simonassi, N. T., & Monteiro, S. N. (2024). Effect of Welding Current on the Dilution and Mechanical Properties of Co–Cr Alloy Stellite-6 Coatings Applied to AISI 4130 Steel. Coatings, 14(12), 1591. https://doi.org/10.3390/coatings14121591

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