Corrosion Behavior of Inconel 625 Coating Produced by Laser Cladding

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Article Corrosion Behavior of Inconel 625 Coating Produced by Laser Cladding

Mieczyslaw Scendo 1,* , Katarzyna Staszewska-Samson 1 and Hubert Danielewski 2

1 Institute of Chemistry, Jan Kochanowski University in Kielce, Uniwersytecka 7, PL-25406 Kielce, Poland; [email protected] 2 Faculty of Mechatronics and Mechanical Engineering, Kielce University of Technology, Al. Tysiaclecia P.P. 7, PL-25314 Kielce, Poland; [email protected] * Correspondence: [email protected]

Abstract: Anti-corrosion properties of Inconel 625 (In) laser cladding coatings onto the (S235JR) steel (S) were investigated. The coatings were produced with the use of wire (WIn/S) or powder (PIn/S). The mechanical properties of the Inconel 625 coatings were characterized by microhardness measurements. The PIn/S shows the highest hardness. The surface and microstructure of the specimens were observed by a scanning electron microscope (SEM). The surface analysis of the laser cladding coatings by energy-dispersive spectroscope (EDS) indicated that the structure of the WIn, and PIn coatings depend on its production technique. The microstructure of the WIn and PIn coatings have a dendritic columnar character. Corrosion test materials were carried out by using electrochemical methods. The corrosive environment was acidic chloride solution. It turned out that the PIn/S coating, which was produced by laser cladding method with the use of Inconel 625 powder, has the best anti-corrosion properties in an aggressive chloride environment. Keywords: superalloy; laser cladding; coating; acidic chloride solution; corrosion parameters Citation: Scendo, M.; Staszewska-Samson, K.; Danielewski, H. Corrosion Behavior of Inconel 625 Coating Produced by Laser Cladding. 1. Introduction Coatings 2021, 11, 759. https:// Nickel-based superalloys, including Inconel 625, are currently used in a variety of doi.org/10.3390/coatings11070759 industries, i.e., aviation, petrochemical, machinery and other industries [1,2]. On the other hand, due to the high cost of nickel-based superalloys, their use may Academic Editor: Hassane Lgaz be highly unproﬁtable. Therefore, one way to reduce component costs is to use nickel- based alloys as coatings to protect cheaper materials. The nickel, as the basic component Received: 19 May 2021 of superalloys, perfectly protects the substrate of materials against corrosion, especially Accepted: 22 June 2021 Published: 24 June 2021 in aggressive electrolytes, which include acid chloride solutions. Moreover, chromium (as the second important component of superalloys) signiﬁcantly increases the resistance

Publisher’s Note: MDPI stays neutral of materials to oxidation, especially in the environment of hot gases containing oxygen with regard to jurisdictional claims in sulfur compounds. On the other hand, chromium (due to its high affinity to oxygen) published maps and institutional affil- forms a durable oxide layer that adheres well to the surface, which perfectly protects the iations. substrate against its further oxidation. It is worth adding that the superalloys contain cobalt and molybdenum in small amounts. Both elements play an important role in protecting materials against pitting and crevice corrosion. Most often, Inconel superalloy coatings have been produced by thermal methods, among them high velocity oxygen fuel [3–5], and atmospheric plasma spray [6]. There are Copyright: © 2021 by the authors. Licensee MDPI, Basel, Switzerland. many disadvantages to coatings produced using both methods. The most important of This article is an open access article these are the large heat affected zone (HAZ) and the porosity of the coating. Therefore, distributed under the terms and other methods of producing protective coatings should be searched for, which allow to conditions of the Creative Commons obtain coatings with much better mechanical and protective properties. Attribution (CC BY) license (https:// The laser rapid manufacturing for superalloy components has the most extensive creativecommons.org/licenses/by/ applications in virtue of fine structure, better mechanical characteristics and lower part distor- 4.0/). tion [7]. Therefore, the authors of the works [8,9] investigated the influence of processing

Coatings 2021, 11, 759. https://doi.org/10.3390/coatings11070759 https://www.mdpi.com/journal/coatings Coatings 2021, 11, 759 2 of 15

parameters on the mechanical properties of laser rapid manufacturing of nickel-based superalloys. However, laser rapid manufacturing technology has several drawbacks at the present development stage. These problems, related to the utilization of a laser beam as heat source for the rapid forming of components, such as high expense, low energy consumption efficiency and safety, significantly limit its practical application [10,11]. The laser cladding (LC) technique seems to be an alternative technique, the use of which allows for the production of good protective coatings. The LC technique is the use of a laser beam to melt the filler material, and partially, the substrate to form a metallurgical coating permanently attached to the substrate. The filling material can be applied directly to the surface of the substrate in the form of a wire or a powder with an appropriately selected composition. For this purpose, appropriately constructed laser heads are used. Typically, during the production of LC coatings, the wire is fed into the laser beam from the side, and the powder coaxially into the laser beam. However, the problem of using lasers to produce coatings and components from different types of materials is still being intensively researched. Moreover, the laser beam is used for the surface polishing, surface geometry formation, surface sealing or for homogenizing the chemical composition of the coatings deposited [12,13]. The corrosion resistance of Inconel alloys over a wide temperature and pressure range has resulted in the widespread use of superalloys in a variety of industries. Laser additive deposition is modern technology using cladding of metals. The deposition process with the use of laser radiation is characterized by high processing precision, low energy consumption, and thus, low deformation of the base material. Moreover, the narrow heat-affected zone (HAZ) influences the use of this technology in advanced applications. The authors [14,15] showed that laser deposition has several advantages over other coating processes, such as thermal spraying. The adhesion between substrate and coating is very strong with minimal dilution where very low HAZ is generated in the substrate. In addition, the porosity of the layer is lower than that observed in thermally sprayed coatings. The repeatability of the process is higher than in the case of other methods of producing thickness coatings. Finally, the LC process is more controlled than thermal spray techniques. Laser cladding and interface evolutions of Inconel 625 alloy on low alloy steel substrate upon heat and chemical treatments was investigated by [16]. The authors cited stated that the laser cladded Inconel 625 layers, typically those areas away from the near-interface regions, regardless of the heat treatment in the molten salts, are strongly resistant to the chemical etching. However, the chemical etching rate of the steel substrate is remarkably affected by the heat treatment; the etching rate at the HAZ is relatively reduced as compared with that at the base materials, which could be related to the increase of compressive residual stress (CRS) in the steel substrate during the heat treatment. The authors in the article [17] described their research results, which concerned the evaluation of the hot corrosion behavior of Inconel 625 coatings on the Inconel 738 substrate by laser and TIG cladding techniques. The resulting coated specimens and the uncoated substrate were subjected to a hot corrosion test carried out at 900 ◦C. As the results indicate, the laser cladded specimen was found to have a noticeably better hot corrosion resistance than the TIG cladded and the uncoated specimens. Interesting research results on the corrosion resistance of 431 stainless coatings produced by a novel surface modification technology, i.e., extreme high speed laser cladding (EHLA) can be found in [18]. Corrosion tests showed that better corrosion resistance was achieved with a higher cladding speed. The uniform distribution of dendrite sizes and composition helped to improve the coating corrosion resistance. High cladding speeds lead to refined dendrites and uniform distribution of composition which were helpful for the improvement of the coating corrosion resistance. So far, there is no information in the literature on the production of protective coatings by laser cladding using Inconel 625 as wire (W) or powder (P) on a steel substrate. In the present study, anti-corrosion properties of Inconel 625 laser cladding coatings onto the S235JR substrate were investigated. The coatings were produced with the use of Coatings 2021, 11, x FOR PEER REVIEW 3 of 14

Coatings 2021, 11, 759 3 of 15 In the present study, anti-corrosion properties of Inconel 625 laser cladding coatings onto the S235JR substrate were investigated. The coatings were produced with the use of Inconel 625 as wire or powder. The corrosion test of the materials in the acidic chloride solutionInconel (1.2 625 M as Cl wire−) were or powder.carried out The by corrosion using the testelectrochemical of the materials methods. in the acidic chloride solution (1.2 M Cl−) were carried out by using the electrochemical methods. 2. Materials and Methods 2. Materials and Methods The coatings were performed using a high power CO2 laser with a Trumpf Lasercell 1005 machineThe coatings (Trumpf were GmbH, performed Ditzingen, using Germany) a high power with CO a laser2 laser cladding with a Trumpfhead that Lasercell had a focal1005 length machine of (Trumpf270 mm GmbH,and was Ditzingen, integrated Germany) with a coaxial with apowder laser cladding feeder (GTV head thatPF 2/2) had a focal length of 270 mm and was integrated with a coaxial powder feeder (GTV PF 2/2) [19]. [19]. The metallic powder was transported through three nozzles of cladding head. On The metallic powder was transported through three nozzles of cladding head. On the other the other hand, the wire was fed to the laser beam zone by means of a roller conveyor. hand, the wire was fed to the laser beam zone by means of a roller conveyor. Moreover, Moreover, the coating production area was protected with a helium stream. Multilayer the coating production area was protected with a helium stream. Multilayer cuboid cuboid specimen using laser deposition technology was manufactured. Layers was specimen using laser deposition technology was manufactured. Layers was cladded cladded alternately alongside X and Y axis until assumed geometry was attained. Process alternately alongside X and Y axis until assumed geometry was attained. Process head head was oriented perpendicular to surface of substrate material, with no inclination at was oriented perpendicular to surface of substrate material, with no inclination at upper upper layers. The following parameters were used to develop a cuboid specimen layers. The following parameters were used to develop a cuboid specimen (320 mm × (320 mm × 120 mm × 5 mm); laser power of 2–6 kW, laser spot diameter of 2.0 mm, 120 mm × 5 mm); laser power of 2–6 kW, laser spot diameter of 2.0 mm, scanning speed of scanning speed of 800 mm/min, powder feed ratio of 15 g/min, and wire diameter of 1.2 800 mm/min, powder feed ratio of 15 g/min, and wire diameter of 1.2 mm, wire feed rate mm, wire feed rate of 900 mm/min. of 900 mm/min. InconelInconel 625 625 superalloy superalloy in in the the form form of of wire wire or or powder powder was was used used to produce aa protectiveprotec- tivecoating coating onto onto the the S235JR S235JR steel. steel. The The chemical chemic compositional composition of theof the steel steel is asis follows:as follows: wt.% wt.%0.200 0.200 C, 0.045C, 0.045 P, 0.045P, 0.045 S, 0.09 S, 0.09 N, andN, and 99.62 99.62 Fe. Fe. S235JR S235JR steel steel is usedis used in in construction construction and andmany many industries. industries. This This steel steel has has good good mechanical mechanical properties, properties, but but is notis not corrosion corrosion resistant re- sistantespecially especially in an in environment an environment ofstrong of strong electrolytes. electrolytes. In In order order to to increase increase the the corrosion corro- sionresistance resistance of S235JRof S235JR steel, steel, an attemptan attempt was was made made to coat to coat its surface its surface with with a layer a layer of Inconel of Inconel625. Before, 625. Before, the steel the surfacesteel surface was cleaned was cleaned by sandblasting by sandblasting method. method. TheThe Inconel Inconel 625 625 powder powder was was delivered delivered by byLPW LPW Technology Technology (Runcorn, (Runcorn, UK), UK), with with particleparticle sizes sizes in inthe the range range of of45–106 45–106 µm,µm, Figure Figure 1.1 .

FigureFigure 1. Morphology 1. Morphology of Inconel of Inconel 625 625 powder. powder.

TheThe shape shape of ofInconel Inconel 625 625 powder powder particles particles was was mostly mostly spherical spherical with with microsatellites microsatellites attachedattached to tothem. them. However, However, several several elongated elongated and and with with irregularly irregularly shaped shaped particles particles were were alsoalso observed. observed. The chemical composition of Inconel 625 wire (BIMO Tech, Wroclaw, Poland) was very similar to that of Inconel 625 powder. However, chemical composition of Inconel 625 feedstock is presented in Table1.

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Table 1. Chemical composition of Inconel 625 feedstock.

Element Ni Cr Nb Mo Si Mn Fe Co Al Ti C wt.% 58.0 21.6 3.6 8.8 0.5 0.5 4.9 1.0 0.4 0.4 0.1

The surface of the S235JR steel was laser cladding with Inconel 625 using wire (WIn) or powder (PIn). The Inconel 625 coatings onto the S235JR substrate (S) were designated as: WIn/S and PIn/S, respectively. The measurement of microhardness of the tested materials was made by the Vickers method (HV), using the Falcon 500 hardness tester of the INNOVATEST (Maastricht, The Netherlands). An indenter was used in the form of a diamond pyramid, whose load varied from 0.02 to 20 N. The depth of indentation was about 3 µm. The surface and microstructure was observed by using a scanning electron microscope (SEM) Joel (Tokyo, Japan), JSM-5400. The accelerating voltage of SEM was 20 kV. The chemical composition of the materials surface were measured by energy dispersive spec- trometer (EDS). Additionally, to observe the surface topography an inverted metallographic microscope (MO) (Delta Optical, Warszawa, Poland), IM-100, was used. The electrochemical measurements (corrosion tests) were carried out by using PG- STAT 128N (Auto Lab, Amsterdam, The Netherlands) potentiostat/galvanostat, piloted by NOVA 1.7 software from the same company. The experiments were carried out in a three electrode cell. The working electrode was made of the S235JR steel without and with Inconel 625 coatings, which were produced using wire (WIn) or powder (PIn). The geometric surface area of the working electrode was 1.0 cm2. The remaining electrode surface was protected against contact with the electrolyte by epoxy glue. Before each measurement, the surface of the electrode was washed with bidistilled water, ultrasonically, and dried at room temperature; afterwards, it was immersed in the test solution, and the measurement was started. The saturated calomel electrode (SCE(KCl)) was used as the reference, and the counter electrode (10 cm2) was made from platinum mesh (99.8% Pt). The supporting electrolyte (corrosive environment) was obtained by mixing the sodium chloride (POCH, Gliwice, Poland), and hydrochloric acid (POCH, Poland), so the concentration of Cl− ion was 1.2 M, and the pH was 1.5. The electrolyte was not deoxygenated. The potentiodynamic polarization (LSV) curves were recorded. All measurements were carried out under a potential range from −1000 to 1200 mV vs. SCE(KCl), whereas the potential change rate was 1 mV·s−1 with holding time of 60 s at −1000 mV in order to clean the electrode surface. The LSV curves were used to designate the corrosion parameters, polarization resistance, and corrosion rate of the tested materials. For this purpose, the method of extrapolation of rectilinear sections of the Tafel potentiodynamic polarization curves were used. The chronoamperometric curves (ChA) were obtained for the potential values which were selected on the basis of the LSV curves for the characteristic points on the LSV curves. For this purpose, one potential value concerned the cathodic process, and two for the anodic process. All measurements were carried out at a temperature of 25 ± 0.2 ◦C, which was main- tained by an air thermostat. However, the electrochemical measurements were repeated three times for each specimen.

3. Results and Discussion 3.1. Vickers Hardness of Materials The hardness (HV) values of the Inconel 625 coatings, which were produced by laser cladding using wire (WIn/S) or powder (PIn/S) are listed in Table 2. The Vickers hardness of the PIn coating is about 311 HV10, and is about fifty units larger compared to the WIn coating (Table 2). It seems that the structure of the PIn coating is fine crystalline and more compact. Therefore, the Inconel 625 coating onto the S235JR steel, which was produced using a powder, should have good mechanical prop- Coatings 2021, 11, 759 erties, including high abrasion resistance. 5 of 15

Table 2. Vickers hardness of Inconel 625 coatings onto the S235JR substrate.

Table 2. Vickers hardnessName Coating of Inconel 625 coatings onto the S235JR substrate. HV10 WIn/S 259 ± 4 Name Coating HV10 PIn/S 311 ± 3 WIn/S 259 ± 4 3.2. Scanning ElectronPIn/S Microscope Images 311 ± 3 Figure 2 shows the scanning electron microscope (SEM) images of the Inconel 625 laser Thecladding Vickers coatings hardness with of the the use PIn of coating wire or is powder about 311 as HV10,feedstock. and The is about microstructure fifty units oflarger deposited compared material, to the WIni.e., coatingInconel (Table 625 onto2). It seemsthe S235JR that the steel structure is assumed of thePIn as coatingdendritic is structurefine crystalline (Figure and 2a,b). more Deposited compact. Therefore, materials theas InconelWIn/S 625and coating PIn/S ontohave thefine S235JR columnar steel, structure,which was with produced characteristic using a oriented powder, parall shouldel haveto deposition good mechanical direction properties, of dendrites. including highIn abrasion both cases, resistance. a dendritic microstructure was observed, which is a typical result of laser-processed materials with high cooling rates. Deposited materials have fine columnar structure,3.2. Scanning with Electron characteristic Microscope oriented Images parallel to deposition direction of dendrites. How- ever, Figurea more2 regular shows dendritic the scanning structure electron was microscopeobtained for (SEM) the PIn images coating of (Figure the Inconel 2b). It 625can belaser assumed cladding that coatings the mechanical with the useproperties of wire of or the powder PIn/S aswill feedstock. be more Thefavorable microstructure than of the of WIn/S.deposited Moreover, material, in i.e., the Inconelcase of 625the ontoPIn coat theing, S235JR a more steel homogeneous is assumed as surface dendritic of structurethe protective(Figure layer2a,b). was Deposited obtained materials compared as WIn/S to the andWIn/S, PIn/S as haveduring fine laser columnar cladding, structure, the coating with materialcharacteristic as Inconel oriented 625 powder parallel was to deposition more evenly direction transferred of dendrites. to the surface of the substrate.

FigureFigure 2. SEMSEM imagesimages of of the the dendritic dendritic structure structure of Inconelof Inconel 625 laser625 laser cladding cladding coatings coatings onto the onto S235JR the S235JRsubstrate substrate with the with use the of: use (a) Wireof: (a or) Wire (b) Powder. or (b) Powder.

OnIn boththe other cases, hand, a dendritic Figure microstructure3 shows the cro wasss-section observed, of the which Inconel is a 625 typical coatings result de- of positedlaser-processed onto the materials S235JR by with laser high cladding cooling meth rates.od Deposited with the materialsuse of wire have or ﬁnepowder. columnar It is worthstructure, noting with that characteristic both coatings oriented are of good parallel quality, to deposition and no pores direction or cracks of dendrites. are visible. How- ever,During a more the regular cladding dendritic process, structure the laser was beam obtained very intensively for the PIn affects coating the (Figure structure2b). Itof thecan substrate be assumed and that the the subsequent mechanical applied properties layers. of The the PIn/Shigh temperature will be more of favorable the laser than beam of createsthe WIn/S. a large Moreover, temperature in the gradient case of thebetween PIn coating, the center a more and homogeneous the edges of the surface melt. of This the producesprotective surface layer was stress obtained gradients compared that are to simi the WIn/S,lar to those as during observed laser during cladding, laser the welding. coating Onmaterial the other as Inconel hand, 625 surface powder stre wasss gradients more evenly were transferred created toby the the surface transport of the ofsubstrate. heat by convectionOn the to other the bottom/inside hand, Figure 3of shows the coat theing, cross-section which was ofinduced the Inconel by electromagnetic 625 coatings deposited onto the S235JR by laser cladding method with the use of wire or powder. It is worth noting that both coatings are of good quality, and no pores or cracks are visible. During the cladding process, the laser beam very intensively affects the structure of the substrate and the subsequent applied layers. The high temperature of the laser beam creates a large temperature gradient between the center and the edges of the melt. This produces surface stress gradients that are similar to those observed during laser welding. On the other hand, surface stress gradients were created by the transport of heat by convection to the bottom/inside of the coating, which was induced by electromagnetic forces in the molten material [20]. Therefore, a different cross-section image was observed for the WIn and PIn coatings (Figure3). However, thickness of the fusion zone (substrate—HAZ) and Inconel 625 coatings onto the S235JR steel are listed in Table3. Coatings 2021, 11, x FOR PEER REVIEW 6 of 14

forces in the molten material [20]. Therefore, a different cross-section image was observed for the WIn and PIn coatings (Figure 3). However, thickness of the fusion zone (substrate—HAZ) and Inconel 625 coatings onto the S235JR steel are listed in Table 3. The fusion zone (substrate—HAZ) layer for the WIn coating is much thicker compared to the PIn coating. Similarly, the WIn coating is thicker compared to the PIn/S Coatings 2021, 11, 759 6 of 15 (Table 3). Therefore, it can be assumed that the mechanical properties of the PIn coating will be greater than that of the WIn/S.

Figure 3. SEM cross-section of Inconel 625 coatings on ontoto the S235JR substrate produced by laser cladding method with the use of: ( a) Wire and (b) Powder.

Table 3. Thickness of the substrate—HAZ and InconelInconel 625625 coatingscoatings ontoonto thethe S235JRS235JR steel.steel.

ThicknessThickness NameName Coating Coating Substrate—HAZSubstrate—HAZ CoatingCoating μmµm μµmm WIn/S 20–33 220–233 WIn/S 20–33 220–233 PIn/S 11–16 180–198 PIn/S 11–16 180–198 3.3. Microstructure of Materials FigureThe fusion 4 shows zone an (substrate—HAZ) example of the layermetallogr for theaphic WIn microstructure coating is much of thicker cross-section compared of theto the Inconel PIn coating. 625 coating Similarly, onto the the S235JR WIn coating steel processed is thicker by compared laser cladding to the PIn/Swith the(Table use3 of). powder.Therefore, However, it can be similar assumed X-ra thaty microanalysis the mechanical of cross-section properties of of the WIn PIn coating coating were will rec- be ordedgreater for than the that Inconel of the 625 WIn/S. coating, which was produced with the use of wire, but they are not presented in this work. 3.3. Microstructure of Materials The Inconel 625 coating was found to adhere well to the substrate. In addition, iron and nickelFigure permeated4 shows an through example the of heat-affected the metallographic zone as microstructure a result of the ofmelting cross-section of Inconel of 625the and Inconel the substrate 625 coating material. onto the Thus, S235JR the laser steel cladding processed process by laser produces cladding a homogeneous with the use structureof powder. of the However, Inconel similar 625 coating X-ray on microanalysis the S235JR substrate. of cross-section of WIn coating were recordedFigure for 5 thedepicts Inconel the 625SEM/EDS coating, image which of was cros produceds-section of with the thePIn use coating, of wire, and but the they re- sultsare not of presentedpoint X-ray in thismicroanalysis work. of the chemical composition of tested material. The averageThe nickel Inconel and 625 chromium coating was content found in tothe adhere tested well coatings to the were substrate. around In wt.%: addition, 55.1 ironand and nickel permeated through the heat-affected zone as a result of the melting of Inconel 19.3 for the WIn/S, and 55.9 and 20.3 for the PIn/S. It is worth noting that more compo- 625 and the substrate material. Thus, the laser cladding process produces a homogeneous nents (i.e., Ni and Cr, and other elements) are transferred to the substrate of S235JR steel structure of the Inconel 625 coating on the S235JR substrate. during laser cladding with Inconel 625 powder. Moreover, the nickel and chromium Figure5 depicts the SEM/EDS image of cross-section of the PIn coating, and the results content is lower in the depth of both WIn/S and PIn/S (Figure 5, spectrum 4–6). Probably of point X-ray microanalysis of the chemical composition of tested material. The average in the cladding process, both elements diffuse deep into the substrate—HAZ. Therefore, nickel and chromium content in the tested coatings were around wt.%: 55.1 and 19.3 for the Inconel 625 coatings adhere well onto the substrate. In addition, nickel, chromium the WIn/S, and 55.9 and 20.3 for the PIn/S. It is worth noting that more components (i.e., and iron permeated through the heat-affected zone as a result of the melting of Inconel Ni and Cr, and other elements) are transferred to the substrate of S235JR steel during laser 625 and the substrate material. cladding with Inconel 625 powder. Moreover, the nickel and chromium content is lower Thus, the laser cladding process produces a homogeneous structure of the Inconel in the depth of both WIn/S and PIn/S (Figure5, spectrum 4–6). Probably in the cladding 625process, coatings both onto elements the S235JR diffuse substrate. deep into the substrate—HAZ. Therefore, the Inconel 625 coatings adhere well onto the substrate. In addition, nickel, chromium and iron permeated through the heat-affected zone as a result of the melting of Inconel 625 and the substrate material. CoatingsCoatings 20212021,, 1111,, x 759 FOR PEER REVIEW 7 7of of 14 15 Coatings 2021, 11, x FOR PEER REVIEW 7 of 14

FigureFigureFigure 4.4. 4. X-rayX-rayX-ray microanalysismicroanalysis microanalysis ofof ofcross-sectioncross-section cross-section ofof PIn ofPIn PIn coatingcoating coating andand and substrate:substrate: substrate: ((aa)) MetallographicMetallographic (a) Metallographic mi-mi- crostructurecrostructuremicrostructure (with(with (with thethe thelineline line scanniscanni scanning),ng),ng), andand and contentcontent content distribution;distribution; distribution; ((bb)) (Iron,Iron,b) Iron, andand and ((cc)) Nickel. (Nickel.c) Nickel.

Figure 5. SEM micrograph, and EDS of PIn coating onto the S235JR substrate, and the results of point FigureFigure 5.5. SEMSEM micrograph,micrograph, andand EDSEDS ofof PInPIn coatingcoating ontoonto thethe S235JRS235JR substrate,substrate, andand thethe resultsresults ofof pointpointX-ray X-rayX-ray microanalysis microanalysismicroanalysis of the ofof chemical thethe chemicalchemical composition compositioncomposition of tested ofof testedtested material. material.material. Thus, the laser cladding process produces a homogeneous structure of the Inconel 625 TheThe studystudy ofof thethe homogeneityhomogeneity ofof thethe structurestructure ofof InconelInconel 625625 coatingscoatings werewere carriedcarried coatings onto the S235JR substrate. outout withwith aa high-qualityhigh-quality methodmethod ofof X-rayX-ray specspectroscopytroscopy withwith electronelectron dispersion.dispersion. FigureFigure 66 The study of the homogeneity of the structure of Inconel 625 coatings were carried presentspresents qualityquality EDSEDS analysisanalysis ofof nickel,nickel, chromium,chromium, niobiumniobium andand molybdenummolybdenum mapmap dis-dis- out with a high-quality method of X-ray spectroscopy with electron dispersion. Figure6 tributiontribution ontoonto thethe WInWIn coating.coating. AA similarsimilar mamapp ofof thethe distributiondistribution ofof elementselements waswas ob-ob- presents quality EDS analysis of nickel, chromium, niobium and molybdenum map distri- tainedtained forfor PIn/S.PIn/S. butionEDS onto analysis the WIn of coating.the basic A chemical similar mapelemen of thets of distribution the WIn and of elementsPIn coatings was onto obtained the for PIn/S.EDS analysis of the basic chemical elements of the WIn and PIn coatings onto the S235JRS235JR substratesubstrate showedshowed aa homogeneoushomogeneous strustructure,cture, withoutwithout disturbingdisturbing thethe decomposi-decomposition.tion. Moreover,Moreover, therethere isis nono differencedifference inin ththee fusionfusion lineline ofof thethe individualindividual layerslayers whichwhich indicatesindicates goodgood mechanicalmechanical andand anti-corrosionanti-corrosion propertiesproperties ofof thethe testedtested coatings.coatings.

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Figure 6. Quality EDS analysis of nickel, chromium, niobium, and molybdenum map distribution of WIn coating.

3.4.FigureFigure Corrosion 6. 6. QualityQuality Test EDS analysis ofof nickel,nickel, chromium,chromium, niobium, niobium, and and molybdenum molybdenum map map distribution distribution of ofWIn WIn coating. coating. Potentiodynamic polarization (LSV) measurement was carried out in order to gain knowledge3.4. CorrosionEDS analysis about Test anti-corrosion of the basic chemical properties elements of Inconel of the 625 WIn laser and cladding PIn coatings coatings onto onto the theS235JR S235JR substrate substrate. showed The acoatings homogeneous were pr structure,oduced withoutby a laser disturbing method theusing decomposition. Inconel 625 Potentiodynamic polarization (LSV) measurement was carried out in order to gain wireMoreover, or powder. there isFigure no difference 7 shows in potentiodyna the fusion linemic of thepolarization individual curves layers of which S235JR indicates steel knowledge about anti-corrosion properties of Inconel 625 laser cladding coatings onto withoutgood mechanical and with Inconel and anti-corrosion 625 coatings properties in an acidic of thechloride tested solution. coatings. the S235JR substrate. The coatings were produced by a laser method using Inconel 625 The process of hydrogen depolarization occurs in the cathode region of the poten- wire or powder. Figure 7 shows potentiodynamic polarization curves of S235JR steel tiodynamic3.4. Corrosion polarization Test curves. On the other hand, oxidation of the surface of S235JR steel without and with Inconel 625 coatings in an acidic chloride solution. or WInPotentiodynamic and PIn was observed polarization in the (LSV)anodic measurement area (Figure 7). was The carried course out of inthe order LSV tocurves gain The process of hydrogen depolarization occurs in the cathode region of the poten- dependknowledge on the about type anti-corrosion and method of properties producing of of Inconel Inconel 625 625 laser coatings cladding onto coatingsthe S235JR onto steel. the tiodynamic polarization curves. On the other hand, oxidation of the surface of S235JR steel However,S235JR substrate. the shift The of the coatings LSV curves were produced toward the by positive a laser method potentials using may Inconel represent 625 wirean in- or or WIn and PIn was observed in the anodic area (Figure 7). The course of the LSV curves creasepowder. in the Figure corrosion7 shows resistan potentiodynamicce of Inconel polarization 625 coatings, curves especially of S235JR the PIn steel coating, without which and depend on the type and method of producing of Inconel 625 coatings onto the S235JR steel. waswith produced Inconel 625 with coatings powder. in This an acidic problem chloride will be solution. discussed extensively later in the article. However, the shift of the LSV curves toward the positive potentials may represent an increase in the corrosion resistance of Inconel 625 coatings, especially the PIn coating, which was produced with powder. This problem will be discussed extensively later in the article.

Figure 7. Potentiodynamic polarization curves of Inconel 625 coatings onto the S235JR substrate Figure 7. Potentiodynamic polarization curves of Inconel 625 coatings onto the S235JR substrate producedproduced by laserlaser claddingcladding method: method: (a) (a) Without Without coating, coating, and and with with the usethe of use (b) of Wire, (b) andWire, (c) and Powder. (c) – Powder.Solutions Solutions contained contained 1.2 M Cl 1.2, pH M 1.5,Cl–, dE/dtpH 1.5, 1 dE/dt mV/s. 1 mV/s. Figure 7. Potentiodynamic polarization curves of Inconel 625 coatings onto the S235JR substrate producedThe by process laser ofcladding hydrogen method: depolarization (a) Without occurscoating, in and the with cathode the use region of (b) of Wire, the potentio- and (c) Powder.dynamic Solutions polarization contained curves. 1.2 M On Cl– the, pH other 1.5, dE/dt hand, 1 mV/s. oxidation of the surface of S235JR steel

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or WIn and PIn was observed in the anodic area (Figure7). The course of the LSV curves depend on the type and method of producing of Inconel 625 coatings onto the S235JR steel. However, the shift of the LSV curves toward the positive potentials may represent an increase in the corrosion resistance of Inconel 625 coatings, especially the PIn coating, which was produced with powder. This problem will be discussed extensively later in the article. It has been demonstrated that the Inconel 625 coatings effectively protect S235JR substrate from contacting with the aggressive corrosive environment (Figure7, curves (a)– (c)). Moreover, the anti-corrosion properties of the Inconel 625 coating depend on the method of producing the coating. The Inconel 625 coating, which was produced using nickel superalloy powder, showed the best anti-corrosion properties (Figure7, curve (c)). It is worth noting that, in the acid corrosive environment, the cathodic branches of the potentiodynamic polarization curves correspond to the simpliﬁed reduction of a hydrogen ion [12,13,21]: 0 + 0 − Me + nH → Me + n H2 − me (1) where Me are the Fe, Ni, Cr, and other metals. It turned out that when the potential of the electrode was changed in the anodic direction, the adsorption layer with the participation of chloride ions [22] was created onto the S235JR surface: 1 Fe0 + Cl− + H+ + O → (FeClOH) (2) 2 2 ads

The adsorption layer of (FeClOH)ads on the electrode surface corresponds to the peaks on the LSV curves which appears for the potential of 10 mV vs. SCE(KCl) (Figure7, curve (a)). The (FeClOH)ads layer partially prevent the electrode surface against further oxidation in the corrosive environment. Unfortunately, the (FeClOH)ads in the acidic chloride solution was dissolved in accordance with a chemical reaction:

+ 2+ − (FeClOH)ads + H → Fe + Cl + H2O (3)

thus, a further sharp increase in the current intensity is observed due to the oxidation of the electrode surface (Figure7, curve (a)). Moreover, a similar reaction mechanism for iron in the acidic chloride environment was proposed by Chin and Nobe [23]. However, when S235JR steel surface was covered with Inconel 625, the anodic reaction was as follows: 0 + − Me + 2H + O2 → (MeO)ads + H2O + me (4)

where (MeO)ads means the (NiO)ads, (Cr2O3)ads, and other oxides. In this case, the electrode surface was covered mainly with a layer of (NiO)ads, and (Cr2O3)ads. Both oxides adhered well to the electrode surface. On the other hand, peaks appeared on the potentiodynamic polarization curves for 415 mV, and 830 mV vs. SCE(KCl) (Figure7, curves (b) and (c)). Thus, under the experimental conditions, the electrode surface covered with the Inconel 625 layer underwent a passivation process. Therefore, a clear inhibition of the corrosion process of the protective coating was observed. The values of the potential (Ec), and critical current density (jc) of the passivation process of the Inconel 625 coatings onto the S235JR substrate were determined. The values of the potential, and critical current density are summarized in Table4.

Table 4. Potential and critical current density of Inconel 625 coatings onto the S235JR substrate.

E j Name Coating c c mV vs. SCE(KCl) µA/cm2 WIn/S 415 38 PIn/S 830 27 Coatings 2021, 11, 759 10 of 15

It turned out that the potential related to the critical current density is the most positive for the Inconel 625 coating (Figure7, curve (c)), which was produced with a powder. A clear shift of the Ec value (about 400 mV) means that the surface of the PIn/S is more resistant to electrochemical corrosion compared to the WIn coating. Moreover, a much lower value of the critical current density for the PIn/S was observed (Table4). However, a much more pronounced effect of protecting the substrate against corrosion was achieved with the Inconel 625 coating, which was produced using a powder. On the other hand, for a more positive electrode potential (about 800 mV, and 1100 mV vs. SCE(KCl), respectively), the alloy surfaces, i.e., WIn/S and PIn/S were depassivated and further oxidation of the tested materials was observed (Figure7, curves (b) and (c)).

3.4.1. Corrosion Parameters The potentiodynamic polarization curves (Figure7) were used to designate the corrosion parameters of the tested materials, i.e., S235JR steel, WIn/S, and PIn/S. For this purpose, the method of the extrapolation of rectilinear sections of the Tafel LSV curves were used [21,22]. The values of the corrosion parameters of the tested materials are listed in Table5.

Table 5. Corrosion parameters of S235JR steel and Inconel 625 coatings.

−b b Ecorr c a jcorr Materials 2 mV vs. SCE(KCl) mV/dec µA/cm S235JR −130 230 120 13.5 WIn/S 210 250 140 4.1 PIn/S 570 350 160 2.4

The corrosion potential (Ecorr) of the investigated materials have shifted signiﬁcantly towards the positive values compared to the S235JR substrate. This means that coating the S235JR steel surface with Inconel 625 makes the material more corrosion resistant under the experimental conditions. Moreover, the PIn coating is the most resistant to electrochemical corrosion in chloride solution. The slope of the cathode (−bc) section of the potentiodynamic polarization curve for PIn/S is about 100 mV higher compared to the WIn/S (Table5). Thus, the mechanism of the cathode process is different on the surface of both electrodes, i.e., WIn/S and PIn/S. Moreover, the anode segment slope (ba) of the LSV curves for both coatings are similar (Table5). This means that the anodic process of WIn/S and PIn/S does not depend on the production method of Inconel 625 coatings onto the S235JR substrate. The lowest value of the corrosion current density (jcorr) was observed for the PIn coating (Table5). So, the most resistant to electrochemical corrosion in a chloride corrosive environment is PIn/S, which was processed by laser cladding method with the use of powder of Inconel 625.

3.4.2. Polarization Resistance and Corrosion Rate

In order to determine the value of the polarization resistance (Rp) of the substrate, and Inconel 625 coatings in an aggressive chloride environment, fragments of potentiodynamic polarization curves (Figure7), which relate to the active dissolution area of the tested materials, i.e., S235JR, WIn/S and PIn/S were selected. The polarization resistance of the electrode is described by the equation:

B Rp = (5) jcorr

and: b × b B = a c (6) 2.303 (ba + bc) Coatings 2021, 11, 759 11 of 15

The Rp values are summarized in Table6. It was found that covering the surface of S235JR steel with Inconel 625 coating increases the polarization resistance of the electrode. The highest polarization resistance was exhibited by the protective oxide coating ((MeO)ads), which was produced by laser cladding onto the S235JR steel with the use of Inconel 625. However, the greatest increase in the Rp value was recorded for the PIn coating (Table6) . This means that the PIn/S is additionally sealed, probably with nickel and chromium oxides. Therefore, during the electrode process, the mass and charge exchange between the electrode and the electrolyte solution slows down.

Table 6. Polarization resistance and corrosion rate of S235JR steel or Inconel 625 coatings.

R CR Materials p mΩ·cm2 mm/Year S235JR 2.5 15.7 WIn/S 9.5 4.7 PIn/S 19.9 2.8

The corrosion rate (CR) of the substrate, and Inconel 625 coatings were calculated based on the equation: CR (mm/year) = 1.16 jcorr (7) which the authors of the works in [24–26] proposed. The surface corrosion rate of S235JR steel is high, i.e., 15.7 mm/year. As a result of covering the substrate surface with the Inconel 625 layer, a drastic reduction in the corrosion rate of the tested materials was observed. It turned out that the CR of the PIn coating is over three times lower compared to that of the WIn/S in an aggressive 1.2 M chloride environment (Table6).

3.5. Chronoamperometric Measurements Figure8 shows the chronoamperometric (ChA) curves of the Inconel 625 coating onto the S235JR substrate. The coating was produced by a laser method using powder (PIn). The potentials of the working electrode was selected based on the potentiodynamic polarization curve (Figure7, curve (c)). One potential value for the cathode process (hydrogen reduction) and two potential values for the anode process (oxidation of the electrode material) were selected. The exposure time of specimens in the aggressive chloride environment (1.2 M Cl−) was ﬁve hours. However, similar ChA curves were recorded for the Inconel 625 coating, which was produced with the use of wire (WIn), but they are not cited in this work. The change in the cathodic current density value depending on the time of electrolysis, the curve (a) (Figure8) relate to the reduction of hydrogen ions onto the surface of the Me electrode (reaction (1)). An unstable change in the current density value means that the surface structure of the electrode changes as it begins to oxidize. The curve (b) (Figure8 ) which was recorded at a potential of 830 mV vs. SCE(KCl) should be attributed to the formation of the adsorption of the (MeO)ads layer onto the Inconel 625 coating (reaction (4)). The electrode surface becomes passivated by adsorption of mainly nickel and chromium oxides. Therefore, under the experimental conditions, a systematic decrease in the current density during electrolysis is observed. Thus, the adsorbed oxide layer is tight and protects the steel substrate well against contact with an aggressive chloride solution. On the other hand, the curve (c) (Figure8) was recorded for a potential of 960 mV vs. SCE(KCl), i.e., in the passive region of Inconel 625. It is also worth noting that in this case, the current density systematically decreases during the duration of the electrolysis. It seems that under these conditions, the adsorbed oxide layer can be additionally sealed by adsorption of Cl– ions [27]: − + MeO + Cl + H → (MeClOH)ads (8) Coatings 2021, 11, x FOR PEER REVIEW 11 of 14

and chromium oxides. Therefore, during the electrode process, the mass and charge exchange between the electrode and the electrolyte solution slows down. The corrosion rate (CR) of the substrate, and Inconel 625 coatings were calculated based on the equation:

CR (mm/year) = 1.16 jcorr (7) which the authors of the works in [24–26] proposed. The surface corrosion rate of S235JR steel is high, i.e., 15.7 mm/year. As a result of covering the substrate surface with the Inconel 625 layer, a drastic reduction in the corrosion rate of the tested materials was observed. It turned out that the CR of the PIn coating is over three times lower compared to that of the WIn/S in an aggressive 1.2 M chloride environment (Table 6).

Table 6. Polarization resistance and corrosion rate of S235JR steel or Inconel 625 coatings.

Rp CR Coatings 2021, 11, 759 Materials 12 of 15 mΩ·cm2 mm/Year S235JR 2.5 15.7 WIn/S 9.5 4.7 The adsorptionPIn/S layer (MeClOH)ads in19.9 the acidic chloride solution was 2.8 dissolved in accordance with a chemical reaction:

3.5. Chronoamperometric Measurements + n+ − (MeClOH)ads + H → Me + Cl + H2O (9) Figure 8 shows the chronoamperometric (ChA) curves of the Inconel 625 coating ontothus, the a further S235JR sharp substrate. increase The in coating the current was intensityproduced is by observed a laser duemethod to the using oxidation powder of (PIn).the electrode surface (Figure7, curves (b) and (c)).

Figure 8. Chronoamperometric curvescurves ofof Inconel Inconel 625 625 coating coating onto onto the the S235JR S235JR substrate substrate produced produced by bylaser laser cladding cladding method method with with the the use use of powder,of powder, obtained obtained for: for: (a) −(a)900 −900 mV; mV; (b) (b) 830 830 mV, mV, and and (c) 960(c) mV.960 mV.Solution Solution contained contained 1.2 M 1.2 Cl −M, pHCl−, 1.5. pH (Dashed 1.5. (Dashed line refers line refers to the to average the average current current density density values). values). 3.6. Inverted Metallographic Microscope Images after Corrosion Test Figure9 shows the inverted metallographic microscope (MO) images of the Inconel 625 coating onto the S235JR substrate without, and with coatings produced by laser cladding method with the use of wire, and powder, after corrosion test in 1.2 M Cl−. The exposure time of the specimens was ﬁve hours. The oxide layer from the surface of tested specimens was removed with diluted nitric acid. In this case, the exposure time was about three minutes. After the removing of the oxide layer from the S235JR substrate, it turned out that the surfaces of the examined steel have undergone electrochemical corrosion in the aggressive chloride environment. It is worth noting large damage of the steel surface, Figure9a as a result of electrochemical corrosion (reactions (2) and (3)). However, Figure9b shows the WIn coating onto the S235JR substrate with was produced by laser cladding method with the use of wire. After exposure of the WIn/S to an aggressive chloride environment, slight damage of the Inconel 625 coating was found as a result of electrochemical corrosion. On the other hand, permanent damage of the WIn coating was observed in the form of deep pits which exposed the substrate material. Moreover, much smaller effects of electrochemical corrosion was observed for the Inconel 625 coating, which was produced with the use of powder, Figure9c . Under the conditions of the experiment, the PIn coating was slightly damaged as a result of the corrosion process in an acid chloride environment. Coatings 2021, 11, 759 13 of 15 Coatings 2021, 11, x FOR PEER REVIEW 13 of 14

Figure 9. MOMO images of Inconel 625 coatings onto the S235JRS235JR substrate:substrate: ( a) Without, and withwith coatings produced byby laserlaser claddingcladding method method with with the the use use of of (b ()b Wire,) Wire, and and (c) ( Powder,c) Powder, after after corrosion corro- − siontest intest 1.2 in M 1.2 Cl M−, Cl pH, 1.5.pH 1.5. Exposure Exposure time time was was ﬁve five hours. hour Corrosions. Corrosion pits pits are markedare marked in red. in red.

4. ConclusionsIt turned out that the most resistance to electrochemical corrosion of the coating was obtainedThe anti-corrosion by laser cladding properties method of Inconel using 625 Inconel coatings 625 onto powder the S235JR as a material substrate for were the investigated.production of The the coatingcoatings onto were the produced S235JR substrate. by laser cladding method with the use of In- conel 625 as wire (W) or powder (P). The microstructure of the WIn and PIn coatings have4. Conclusions a dendritic columnar character, with the dendrite orientation related to the direction of crystallization.The anti-corrosion The Inconel properties 625 ofcoating Inconel pr 625oduced coatings with ontothe use the S235JRof powder, substrate i.e., PIn/S, were showsinvestigated. the highest The coatings hardness were compared produced to bythe laser WIn/S. cladding In an method acid chloride with the solution use of Inconel(1.2 M Cl625−1.2M as), wirethe WIn (W) and or powderPIn coatings (P). Theonto microstructure the S235JR steel of were the WInpassivated. and PIn The coatings oxide layers have ((NiO)a dendriticads, (Cr columnar2O3)ads, and character, other metals with theadditionally dendrite protects orientation WIn/S related and toPIn/S the directionagainst cor- of rosion.crystallization. However, The the Inconel corrosion 625 coatingrate of the produced PIn coating with theis over use ofthree powder, times i.e.,lower PIn/S, in relation shows −1.2M tothe the highest WIn/S hardness in the aggressi comparedve chloride to the WIn/S. environment. In an acid chloride solution (1.2 M Cl ), the WIn and PIn coatings onto the S235JR steel were passivated. The oxide layers ((NiO)ads, Author(Cr2O3 )adsContributions:, and other metalsConceptualization, additionally M.S.; protects Formal WIn/S analysis, and PIn/SM.S.; Investigation, against corrosion. H.D.; Metodology,However, the M.S.; corrosion Writing-original rate of the draft, PIn M.S. coating and isK.S.-S.; over threeWriting-review times lower and in editing, relation M.S. to theAll WIn/Sauthors have in the read aggressive and agreed chloride to the published environment. version of the manuscript. Funding: This research was funded by NCBiR, grant number LIDER/31/0173/L-8/16/NCBR/2017: Technology of manufacturing sealed weld joints for gas installation by using concentrated energy source.

Coatings 2021, 11, 759 14 of 15

Author Contributions: Conceptualization, M.S.; Formal analysis, M.S.; Investigation, H.D.; Metodol- ogy, M.S.; Writing-original draft, M.S. and K.S.-S.; Writing-review and editing, M.S. All authors have read and agreed to the published version of the manuscript. Funding: This research was funded by NCBiR, grant number LIDER/31/0173/L-8/16/NCBR/2017: Technology of manufacturing sealed weld joints for gas installation by using concentrated energy source. Institutional Review Board Statement: Not applicable. Informed Consent Statement: Informed consent was obtained from all subjects involved in the study. Data Availability Statement: Data available in a publicly accessible repository. Conﬂicts of Interest: The authors declare no conﬂict of interest.

References

1. Verdi, D.; Garrido, M.A.; Munez, C.J.; Poza, P. Cr3C2 incorporation into an Inconel 625 laser cladded: Effects on matrix microstructure, mechanical properties and local scratch resistance. Mater. Des. 2015, 67, 20–27. [CrossRef] 2. Cooper, D.; Thornby, J.; Blundell, N.; Henrys, R.; Williams, M.A.; Gibbons, G. Design and manufacture of high performance hollow engine valves by additive layer manufacturing. Mater. Des. 2015, 69, 44–55. [CrossRef] 3. Ahmed, N.; Bakare, M.; McCartney, D.; Voisey, K. The effects of microstructural features on the performance gap in corrosion resistance between bulk and HVOF sprayed Inconel 625. Surf. Coat. Technol. 2010, 204, 2294–2301. [CrossRef] 4. Al-Fadhli, H.; Stokes, J.; Hashmib, M.; Yilbas, B. HVOF coating of welded surfaces: Fatigue and corrosion behaviour of stainless steel coated with Inconel-625 alloy. Surf. Coat. Technol. 2006, 200, 4904–4908. [CrossRef] 5. Al-Fadhli, H.; Stokes, J.; Hashmib, M.; Yilbas, B. The erosion-corrosion behaviour of high velocity oxy-fuel (HVOF) thermally sprayed inconel-625 coatings on different metallic surfaces. Surf. Coat. Technol. 2006, 200, 5782–5788. [CrossRef] 6. Ramesh, C.; Devaraj, D.; Keshavamurthy, R.; Sridhar, B. Slurry erosive wear behaviour of thermally sprayed Inconel-718 coatings by APS process. Wear 2011, 271, 1365–1371. [CrossRef] 7. Theriault, A.; Xue, L.; Dryden, J.R. Fatigue behavior of laser consolidated IN-625 at room and elevated temperatures. Mater. Sci. Eng. A 2009, 516, 217–225. [CrossRef] 8. Ganesh, P.; Kaul, R.; Paul, C.P.; Tiwari, P.; Rai, S.K.; Prasad, R.C.; Kukreja, L.M. Fatigue and fracture toughness characteristics of laser rapid manufactured Inconel 625 structures. Mater. Sci. Eng. A 2010, 527, 7490–7497. [CrossRef] 9. Paul, C.P.; Khajepour, A. Automated laser fabrication of cemented carbide components. Opt. Laser Technol. 2008, 40, 735–741. [CrossRef] 10. Dinda, G.; Dasgupta, A. Majumder, Laser aided direct metal deposition of Inconel 625 superalloy: Microstructural evolution and thermal stability. J. Mater. Sci. Eng. A 2009, 509, 98–104. [CrossRef] 11. Tabernero, I.; Lamikiz, A.; Martínez, S.; Ukar, E.; Figueras, J. Evaluation of the mechanical properties of Inconel 718 components built by laser cladding. J. Int. J. Mach. Tools Manuf. 2011, 51, 465–470. [CrossRef] 12. Scendo, M.; Trela, J.; Radek, N. Inﬂuence of laser power on the corrosive resistance of WC-Cu coating. Surf. Coat. Technol. 2014, 259, 401–407. [CrossRef] 13. Scendo, M.; Radek, N.; Trela, J. The inﬂuence of electrospark and laser treatment upon corrosive resistance of carbon steel. Adv. Mater. Res. 2014, 874, 107–112. [CrossRef] 14. Weng, F.; Chen, C.; Yu, H. Research status of laser cladding on titanium and its alloys: A review. Mater Des. 2014, 58, 412–425. [CrossRef] 15. Abioye, T.E.; McCartney, D.G.; Clare, A.T. Laser cladding of Inconel 625 wire for corrosion protection. J. Mater. Process. Technol. 2015, 217, 232–240. [CrossRef] 16. Liu, H.; Tan, C.K.I.; Wei, Y.; Lim, S.H.; Lee, C.J.J. Laser-cladding and interface evolutions of inconel 625 alloy on low alloy steel substrate upon heat and chemical treatments. Surf. Coat. Technol. 2020, 404, 126607. [CrossRef] 17. Fesharaki, M.N.; Shoja-Razavi, R.; Mansouri, H.A.; Jamali, H. Evaluation of the hot corrosion behavior of Inconel 625 coatings on the Inconel 738 substrate by laser and TIG cladding techniques. Opt. Laser Technol. 2019, 111, 744–753. [CrossRef] 18. Shen, F.; Tao, W.; Li, L.; Zhou, Y.; Wang, W.; Wang, S. Effect of microstructure on the corrosion resistance of coatings by extreme high speed laser cladding. Appl. Surf. Sci. 2020, 517, 146085. [CrossRef] 19. Danielewski, H.; Antoszewski, B. Properties of laser additive deposited metallic powder of Inconel 625. Open Eng. 2020, 10, 484–490. [CrossRef] 20. Fuhrich, T.; Berger, P.; Hügel, H. Marangoni effect in laser deep penetration welding of steel. Laser Appl. 2001, 13, 178–186. [CrossRef] 21. Staszewska, K.; Scendo, M. Mechanism and kinetics oxidation of Inconel 617 and 625 alloys. Tech. Issues 2016, 1, 82–89. 22. Scendo, M.; Staszewska-Samson, K. Effect of temperature on anti-corrosive properties of diamond-like carbon coating on S355 steel. Materials 2019, 12, 1659. [CrossRef][PubMed] Coatings 2021, 11, 759 15 of 15

23. Chin, R.J.; Nobe, K. Electrodissolution kinetics of iron in chloride solutions. J. Electrochem. Soc. 1972, 119, 1457–1461. [CrossRef] 24. Jiang, J.; Yu, L.; Gan, F. High temperature naphthenic acid corrosion of steel in high TAN refining media. Anti-Corros. Methods Mater. 2008, 55, 257–263. [CrossRef] 25. Quej Ake, L.M.; Contreras, A.; Aburto, J. The effect of non-ionic surfactant on the internal corrosion for X52 steel in extra-heavy crude oil-in-water emulsions. Anti-Corros. Methods Mater. 2018, 65, 234–248. [CrossRef] 26. Yang, G.; Song, W.; Wang, F.; Ma, Y.; Hao, Y. Corrosion behavior of 20# steel in aqueous CO2 solution under stratified gas-liquid two-phase flow condition. Anti-Corros. Methods Mater. 2019, 66, 11–18. 27. Scendo, M.; Spadlo, S.; Staszewska-Samson, K.; Mlynarczyk, P. Influence of heat treatment on the corrosion resistance of aluminium-copper coating. Metals 2020, 10, 966. [CrossRef]