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Tribological Behavior of Ni-Based WC-Co Coatings Deposited via Spray and Fuse Technique Varying the Oxygen Flow

Tribological Behavior of Ni-Based WC-Co Coatings Deposited via Spray and Fuse Technique Varying... Hindawi Advances in Tribology Volume 2021, Article ID 8898349, 10 pages https://doi.org/10.1155/2021/8898349 Research Article Tribological Behavior of Ni-Based WC-Co Coatings Deposited via Spray and Fuse Technique Varying the Oxygen Flow 1,2 1 3 H. Jime´nez , J. J. Olaya , and J. E. Alfonso Department of Mechanical Engineering and Mechatronics, Universidad Nacional De Colombia, Street 45, 26-85, Bogota´, Colombia Research Group in Energy and Materials (REM), Faculty of Mechanical Engineering, Universidad Antonio Narino, Bogota, Colombia Ciencia De Materiales y Superficies, Physis Department, Universidad Nacional De Colombia, Street 45, 26-85, Bogota´, Colombia Correspondence should be addressed to J. E. Alfonso; jealfonsoo@unal.edu.co Received 10 May 2020; Accepted 24 March 2021; Published 20 May 2021 Academic Editor: João P. Davim Copyright © 2021 H. Jime´nez et al. +is is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. +e tribological behavior of Ni-based WC-Co coatings is analyzed. +e coatings were deposited on gray cast iron substrates in a spray and fuse process using SuperJet Eutalloy deposition equipment, varying the oxygen flow conditions in the flame. +e crystallographic structure of the coatings was characterized via the X-ray diffraction (XRD) technique. +e microhardness was measured on the surface and in cross sections of the coatings by means of a Knoop microhardness tester. +e topography and the morphological characteristics of the coatings and the tribo-surfaces were examined using scanning electron microscopy (SEM) and confocal microscopy, while the chemical composition was measured by means of energy-dispersive X-ray spectroscopy (EDS). +e tribological behavior of the coatings was examined via a cohesion-adhesion scratch test, using cross sections of the coatings. Furthermore, two wear tests were carried out, using the pin-on-disk method under ASTM G99 standard and an ASTM standard G65 sand/rubber wheel abrasion wear test. +e wear of the coatings showed a close relationship to the porosity in the metal matrix; since then, in the abrasive wear test, a high porosity is related with lower hardness in the coatings; likewise, a low hardness is related with a high wear. coatings have been used in applications such as protection 1. Introduction against abrasive wear for industrial tools [5, 6]. WC-Co coatings are frequently used in wear-resistance Some applications of the cermet coatings have been applications due to their tribological properties [1, 2]. reported by some authors like Szymanski ´ et al., who found +ese coatings have been deposited mainly using thermal that coatings produced by thermal spray techniques have spray techniques, such as high-velocity oil fuel (HVOF), shown high resistance to corrosion and erosion in industry arc spray, plasma spraying, and detonation spray coating applications. Cavitation erosion tests were performed on [3, 4]. +e spray and fuse thermal spray process has im- coatings deposited by the HBOF technique according with portant advantages compared to other thermal spray the ASTM G32 standard, identifying sliding wear mecha- techniques due to the ease of production of the coatings, nisms and cavitation in coatings. Likewise, failure analysis of the wide variety of geometries and surfaces that can be cermet coatings deposited by HBOF technique showed that coated, the relatively low cost of coating production, and Yttria reinforced WC-10Co4Cr coating has superior tribo- the ease of handling of the equipment. Furthermore, resistance and mechanical properties, while WC-10Co4Cr coatings produced using this technique have a lower de- coating showed good wear resistance in fly ash slurry which gree of porosity and high adhesion to the substrate. +ese possesses a weak acidic nature. +e mechanical properties of 2 Advances in Tribology the Ni-based alloy/nano-h-BN self-lubricating composite 600 s and 400 g of load using a steel ball of 838 HV of coatings were analyzing by Zhang et al., who found that the hardness and 10 mm in diameter and a test speed of 10 cm/s. average microhardness of the coatings was influenced by the Additionally, we used the ASTM G-65 test under the B addition of solid lubricant in the powder feedstocks [7–10]. procedure (130 N of load and 2000 revolutions of the wheel In the present investigation, we describe the tribological to obtain ∼1436 m of wear distance). behavior of Ni-based WC-Co coatings deposited via the spray and fuse technique and evaluate the tribological be- 3. Results and Discussion havior as a function of the oxygen flux. +e reports regarding the variation of the oxygen flow in thermal spray systems are 3.1. XRD Analysis. In a previous investigation [16], we found extensive, and authors such as Bandgopadhyag et al. and that the XRD pattern that corresponds to MetaCeram Nylen used computer software to model the effect of the powder exhibits Ni B and Ni peaks with Ni reflections in oxygen flow on the distribution of speeds and temperatures crystallographic planes (111), (200), (220), (311), and (222), in an oxyacetylene flame. +e heat power P dissipated by the according to the X’Pert HighScore card, with reference code: flame depends on the fuel/oxidant ratio and the fuel gas feed 03-065-2865. WC (hex) (001), (100), and (101), and W C and rate, mu; as the limiting factor in combustion is mO , it can metallic W peaks were detected, due to the decarburization process of the WC particles, according to the cards with be said that P is proportional to the oxygen flow. +erefore, the oxygen flow is a very important parameter in mechanical reference code 00-051-0939 and 01-070-2633. +is crystal- and tribological properties of the coatings grew via thermal lographic structure of the MetaCeram was reproduced in the spray technique; however, the reports found in the literature coatings produced under different oxygen flow conditions. in this regard are poor [11–15]. Additionally, in the coatings, a B O peak, with reflections in 2 3 crystallographic plane (310), appears in the patterns. +e crystallite size was determined using the Williamson–Hall 2. Experimental Setup method. Using the spray and fuse thermal spray technique, Ni-based WC-Co coatings were deposited on gray cast-iron cylin- 3.2. Microhardness. According to Paneto et al. [17], in order drical substrates of 41 mm in diameter and 4 mm in to calculate the theoretical hardness (HV ) of composite thickness, varying the oxygen flow in the oxyacetylene flame materials, such as MetaCeram coatings, it is necessary to four times, with the objective to obtain carburizing, neutral, consider the molar fractions of the deposited constituents and oxidizing flames. +e substrates were cleaned using a multiplied by their respective theoretical hardness. For commercial degreasing liquid and subsequently immersed in MetaCeram, the main elements of the flux powder are taken an ultrasonic bath for 10 minutes. A commercial powder as wt%, which are in the following order: Ni at 44%, WC/Co called MetaCeram was used for filler material. In the de- at 40%, and Cr at 9.3%. To calculate the theoretical hardness, position process of the coatings, the gray cast iron substrate the relationship used is, is preheated to temperatures between 500 and 600 C, then the filler material is sprayed onto the substrate, and then this HV � A630 􏼁 + B2050 􏼁 + C90 􏼁 , (1) 0 HV HV HV material is melted onto the substrate, forming the coating. +e deposition conditions are summarized in Table 1. +e where A is the molar fraction of Ni, B is the molar fraction of parameters of the pressure of the gases, the distance between WC, C is the molar fraction of Cr, 630 HV is the theoretical the spraying and fuse, and the nozzle type were given by the hardness of 100% dense Ni, 2050 HV is the theoretical manufaturater of MetaCeram powders. hardness of 100% dense WC/Co, and finally 90 HV is the +e crystalline structure of the coatings was analyzed theoretical hardness of 100% dense Cr. Using equation (1), using the X-ray diffraction (XRD) technique. +e XRD the theoretical hardness of the MetaCeram coatings was patterns were obtained with Panalytical equipment in calculated obtaining a value of 1105.57 HV10850 MPa. +is Bragg–Brentano geometry with Cu Kα radiation of value is very close to the average microhardness values ˚ ° λ � 1.5406 A and a step of 0.02 . To determine the crys- registered for the coatings in Table 2 for the coatings de- tallographic planes of the coatings, X´Pert HighScore soft- posited at different oxygen fluxes. +ese values are the result ware was used. Using scanning electron microscopy (SEM) of the average of the hardness taken on the diametric lines of and confocal laser microscopy, the morphology and the the surface of the coatings, with three control samples for topographical details of the coatings were analyzed, as well as each deposit. the wear tracks, in order to determine the wear mechanisms Figure 1 shows the variation in the microhardness with the crystallite size in the metallic Ni matrix and the WC/Co of the coatings. +e chemical analyses of the coatings and the wear tracks were carried out by means of energy-dispersive particles. +e graph shows that coatings with a crystallite size X-ray spectroscopy (EDS) using a FEI Quanta 200-r of 50 nm in the Ni matrix and 67 nm in the WC/Co matrix equipment. reach a maximum value of the microhardness. Additionally, a Microhardness measurements were carried out using a noticeable decrease in microhardness is also recorded for Knoop scale LECO micro indenter, with 300 g of load and crystallite values close to 10 nm, which is in accordance with 15 s of dwell time. +e wear measurement was made using the Hall–Petch theory which indicates that the yield stress and the ASTM G99-04 test, with a pin-on-disk CETR-UMT-2- hence the hardness are related with the inverse square root of 110 tester, working at room temperature, with a test time of crystallite size [18, 19]. Moreover, Sriraman et al. [20] report Advances in Tribology 3 Table 1: Deposition conditions of the MetaCeram coatings. Brand of torch SuperJet Eutalloy O pressure (psi) 39 (268.896 kPa) C H pressure (psi) 7 (48.2633 kPa) 2 2 O flow (SCFH) 11.04 12.88 14.72 16.56 C H flow (SCFH) 14.64 2 2 Powder code MetaCeram 23075 Powder composition 44Ni, 40WC/Co, 9.3Cr, 1.9 B, 2.1Fe, 2.3Si, 0.4 C. Spraying-fusion distance 150–20 mm Nozzle B2 Table 2: Average values of surface microhardness of MetaCeram coatings deposited at different oxygen fluxes. MetaCeram samples Average microhardness (MPa) +ickness (µm) Steel ball 8218± 94,31 Substrate 347.48± 54 - MetaCeram (theoretical value) 10850 - (11.04 SCFH) 9448.09± 32.15 228.41± 6.42 (12.88 SCFH) 10470.64± 61.23 230.53± 4.14 (14.72 SCFH) 10092.27± 12.95 270.14± 9.03 (16.56 SCFH) 9010.88± 67.65 250.16± 2.97 +e microhardness values summarized in Table 2 were made on the surface of the coatings since other values of the microhardness were made on the transversal section. 70 70 results obtained from the characterization carried out using the potentiodynamic polarization technique on the substrate and the coatings in a previous paper, and the average error in the 60 60 porosity measurement was 0.021% [16]. Figure 2 shows the cross section of the MetaCeram coatings; in this figure, the 50 50 pores of the coatings are clearly appreciated. Figure 3 shows the variation of the microhardness as a function of the porosity. It 40 40 is clear that large porosity values result in a decrease in the hardness of the deposits. +is behavior can be explained since 30 30 the load indenter did not find material in the porous places. 20 20 3.3. Scratch Test. Figure 4 shows the tracks for the scratch 8800 9000 9200 9400 9600 9800 1000010200 10400 10600 tests performed on the MetaCeram coatings for a load of Microhardness (MPa) 15 N. +e area of the cones was obtained via optical mi- Figure 1: Crystallite sizes of Ni matrix and WC-Co particles as a croscopy with image analyzer. +e scratch resistance values function of microhardness. obtained under the application of ISO/WD 27307 are summarized in Table 3. +e coefficient of variation (Vr) is determined according to, that refinement of the crystallite size of Ni W alloys results in an increase in the hardness of the material. As the micro- � ∗ 100%, (2) structure of the material is refined, the elastic limit or the hardness of the material increases and then decreases, after reaching a maximum yield stress threshold. Several studies where ρ represents the standard deviation and μ is the average value of the cone area [21, 22]. have established this threshold at values between 10 and 40 nm. +e effect of crystallite size on the tensile strength can In these coatings, the 5 N load did not generate a de- be analyzed from the theory of dislocation; thus, the plastic tectable scratch trace, due to their high hardness, while with deformation of the material must be able to overcome the a load of 10 N, although it was possible to appreciate the maximum stress, which increases the density of the dislo- scratch tracks and the formation of cones in the substrate- cations. A small crystallite size generates a greater number of coating interface and in the superficial zone, the propagation borders between crystals, and this hinders the movement of of cracks through the scratch pattern was not clearly seen. For the scratch tests performed with 15 N, the formation of a the dislocations, and the maximum tensile stress in a plastic deformation is strongly influenced by the average size of the cone at the substrate-coating interface as well as the surface of the cone was much clearer. +ese formations could crystallite and the morphology of the particle. +e reduction in microhardness is also highly influenced suggest that the failure in these coatings is both adhesive and cohesive. However, in the absence of clear cracking of the by porosity. +e porosity index was calculated through the Crystallite size Ni (nm) Crystallite size WC (nm) 4 Advances in Tribology Unmelted particles Pores Resign Coating Substrate HV Mag Sig WD 500.0µm Universidad Nacional de Colombia 25.0 kV 200× SE 8.7 mm Figure 2: MetaCeram coatings’ cross section. 0.15 0.20 0.25 0.30 0.35 0.40 0.45 Porosity (vol %) Figure 3: Microhardness vs porosity of MetaCeram coatings. substrate-coating interface, it can also be assumed that the were calculated according to equations (3) and (4), respectively. formation of the cone in the adhesive zone could be a +e worn volume calculation indicates that the coating did not product of the high hardness difference between the gray exhibit significant wear since wear occurs mainly on the pin cast iron substrate and the coating, which can cause an because the average hardness of the coating is greater than that abrupt change in the degree of penetration of the indenter of the pin. +is can be seen in Figure 6, which was taken with when passing from substrate to coating. confocal laser microscopy on the wear track. In the cohesive failure zone, the coating is separated by πD (3) V � , means of the scratch test for the 15 N load, and the release of 64d WC/Co particles or nonmolten particles was detected using where D represents the diameter of the pin and d is the the scratch test, which demonstrates that the carbide par- diameter of the wear track. ticles do not completely melt with the metallic Ni matrix of V 􏼐mm 􏼑 the coating. +e area of the cone was shown to be related to (4) K � , L(N)d(mm) the degree of porosity of the coatings: the coatings with a higher degree of porosity recorded higher values of the area where V is the worn volume and L is the load. of the cone of cohesive failure. In general, the coatings of MetaCeram showed that the wear coefficient K and the COF change appreciably at higher 3.4. Pin-on-Disk Wear Test. Figure 5 shows the friction co- oxygen flux in the flame. +is is probably due to the fact that efficient (COF) curves for the MetaCeram coatings deposited the products with a higher degree of hardness, such as WC/ under different oxygen flow conditions. +e COF of the Co, aggregate in the Ni matrix, which results in less effective coatings was obtained from the stable area of the graphs. By contact friction. +e results obtained in the adhesive wear means of optical microscopy using image analyzer, the average tests are in agreement with previous studies. Authors such as Torgerson et al. [23] report the formation of NiO layers in width of the wear tracks was obtained, in order to calculate the worn volume and the wear coefficient. Table 4 records the nickel-based coatings deposited via cold thermal spraying. +ese authors found that the formation of NiO layers re- parameters of the pin-on-disk test carried out on the Meta- Ceram coatings. +e worn volume and the wear coefficient duces the coefficient of friction. Likewise, WC particles Microhardness (MPa) Advances in Tribology 5 Figure 4: Scratch test of MetaCeram coatings. provided resistance to thermal softening and helped to +e images do not reveal furrows of abrasive wear; this improve the wear resistance at elevated temperatures. confirms that the wear mechanism for these coatings is Figure 7 shows the deterioration undergone by Meta- mainly due to adhesive wear produced by the oxides, evi- Ceram coatings in the course of the pin-on-disk wear test. denced by the XRD study and possible oxides formed during 16.6 SCFH 14.2 SCFH 12.8 SCFH 11.04 SCFH 6 Advances in Tribology Table 3: Average results of scratch resistance of MetaCeram coatings. Coating O flow (SCFH) Scratch test load (N) Projected cone area A (µm ) Variation coefficient Vr (%) Failure 2 c 5 — — - 11.04 10 9089.8 17.25 Adhesive/cohesive 15 11284 18.41 Adhesive/cohesive 5 — — - 12.88 10 3224.34 20.05 Adhesive/cohesive 15 6280.75 19.16 Adhesive/cohesive MetaCeram 5 — — - 14.72 10 1685.4 18.21 Adhesive/cohesive 15 1870.26 20.84 Adhesive/cohesive 5 — — - 16.56 10 8282 19.45 Adhesive/cohesive 15 17289 18.37 Adhesive/cohesive 0.7 0.6 0.5 0.4 0.3 0.2 0.1 100 200 300 400 500 600 Time (s) 11.04 (SCFH) 14.72 (SCFH) 12.88 (SCFH) 16.56 (SCFH) Figure 5: Coefficient of friction (COF) as a function of the time curves of MetaCeram coatings. Figure 6: Pin-on-disk wear tracks of MetaCeram coatings obtained by confocal microscopy. Table 4: Pin-on-disk test parameters of MetaCeram coatings. +e behavior of the wear rate as a function of the MetaCeram VW (MM3) K COF microhardness is illustrated in Figure 8. In the figure, it is (11.04 SCFH) 0.032± 0.061 8.03 E-8± 0,11 0.662± 0.022 evident that the wear coefficient increases with the (12.88 SCFH) 0.016± 0.037 1.05 E-8± 0,04 0.621± 0.013 microhardness. (14.72 SCFH) 0.025± 0.032 5,36 E-8± 0,23 0.423± 0.046 (16.56 SCFH) 0.054± 0.071 8.93 E-8± 0,07 0.675± 0.036 3.5. Abrasive Wear Test. +e abrasive wear tests of the gray cast substrates and the MetaCeram coatings were carried out the wear test. +e images also show that the WC particles do following procedure B of the ASTM G-65 rubber-wheel test not undergo significant deterioration after the wear test; on standard, which specifies a load of 130 N with 200-wheel the contrary, they act as accumulation points for worn revolutions, which generates 1436 m of wear distance using material, which prevents the abrasive wear mechanism. Ottawa sand as abrasive. Using Archard’s equation (equa- Some areas of the coatings showed microcracks at points tion (5)), the wear coefficient was calculated. For this, it was with defects such as nonmolten particles or pores on the necessary to determine the volume of worn material, which wear track. was obtained using equation (6). +e wear mechanism evident in the pink-on-disk test showed that the points, the contact between coating surface K∗ L∗ x V � , (5) and wear ball (contact points), are generate peaks or roughness own of the coatings deposited at high oxygen m − m pressure (16.56 SCFH). +e points of contact are broken and i f (6) V � (1000), regenerated as the test develops. Friction coefficient Advances in Tribology 7 Figure 7: SEM micrographs of pin-on-disk wear tracks of MetaCeram coatings. where K is the wear coefficient, V(mm ) is the wear volume Figure 9 shows the wear tracks of the MetaCeram of the softest material, H(GPa) is the hardness of the sample, coatings. It is possible to see the deterioration undergone by L(N) is the force exerted on the specimen, x(m) is the linear these coatings due to the abrasive wear tests. +e type of abrasion value, and mi and mf represent, respectively, the damage recorded was similar for all coatings, independent of initial and final values of the mass of the samples analyzed. the oxygen flow at which they were deposited. In the graphs, Metaceram 16.56 SCFH MetaCeram 14.72 SCFH Metaceram 12.88 SCFH MetaCeram 11.04 SCFH 8 Advances in Tribology 9000 9500 10000 10500 Microhardness (MPa) Figure 8: Microhardness vs wear coefficient of MetaCeram coatings. (a) (b) (c) Figure 9: SEM micrograph of wear traces for MetaCeram coatings. Co, following a line of fracture that borders these individual the presence of shallow grooves, a product of a micro- plowing mechanism, is evident. +ese furrows are produced structures, which allows us to infer a cohesion failure in by the displacement and later accumulation of the material them. It can also be seen how the fracture of these areas in front of the abrasive particles. +e particles of WC/Co in propagates to the metal matrix of the coating. +ese results the metallic Ni matrix of the MetaCeram coating act as are in agreement with those reported by St-Georges [24], accumulators of the detached material and even of the who found a mechanism of attrition by removal of the abrasive. +e accumulation of this material in specific zones metallic binder matrix in Ni-Cr + WC coatings, also re- can cause stress concentrations that lead to plastic defor- cording little evidence of fragmentation of WC particles. mation of the ductile areas of the coating, which are those Likewise, Liyanage et al. [25] recorded the phenomenon of where the concentration of Ni is predominant. +e mech- crack propagation for WC agglomerates in Ni-WC coatings. anism of microplowing is recorded in the graphs as dete- +e geometry of the cracking reported by these authors coincides with that reported in the present investigation. rioration zones 1 and 2, which are highlighted by circumference and rectangles; likewise, the zone where there Table 5 records the abrasive wear parameters obtained is plastic deformation is identified with the number 3 and is for MetaCeram coatings. +e results show a lower degree of highlighted with an oval. wear than the gray cast substrate. +is is due to the presence +e graphs also record the formation of microcracks, of the WC/Co system in the metallic Ni matrix in the mainly in areas rich in WC/Co. +is is due to the fragility of MetaCeram coatings. Both the wear rate and the wear co- the WC/Co particles and the high surface tension caused by efficient recorded showed a close relationship with the sliding of abrasive (sand) with these particles, which produce hardness and porosity of the coatings. Figure 10 shows the regions of acumulation, the abrasive and detached materials, variation of the microhardness as a function of the wear rate that increase the net pressure on the coating-substrate in- and the degree of porosity of the MetaCeram coatings. terphase. Figure 9(c) shows how the fracture occurs between +is graph shows a clear, decreasing relationship be- tween the microhardness and the wear rate. +ese results the individual grains that make up the regions rich in WC/ ∗ –8 3 ∗ Wear rate ( 10 mm /N mm) Advances in Tribology 9 Table 5: Gray cast iron substrate and MetaCeram coatings’ adhesive wear parameters. 3 −4 −5 3 Sample Mass loss (g) Worn volume (mm ) Wear coefficient K (×10 ) Wear rate W (×10 mm /Nm) MetaCeram (11.04 SCFH) 0.1238± 0,0048 13.601 3,441 3.6420 MetaCeram (12.88 SCFH) 0.0410± 0,0037 4.5064 1.218 1.2067 MetaCeram (14.72 SCFH) 0.0793± 0,0094 8.7133 2.443 2.3332 MetaCeram (16.56 SCFH) 0.1967± 0,0081 21.617 5.216 5.7885 (iii) +e porosity of the coatings increases with the 0.48 oxygen flow, which produces a decrease in their microhardness. 0.40 (iv) For all flows of oxygen used in the deposit of the 10000 coatings, cohesion and adhesion wear mechanisms 0.32 were simultaneously present. (v) In the stable zone of the coatings, the lowest COF 9500 was obtained in the coatings deposited with 14 0.24 SCFH oxygen flow. (vi) +e decarburization process negatively affected the 0.16 mechanical and tribological properties of Meta- Ceram coatings, both due to a reduction in hard- ness due to the degradation of WC in W C and 12 3 45 6 4 3 metallic W, as well as the increase in porosity due to Wear rate (×10 mm /Nm) the Kirkendall effect. Figure 10: Microhardness and porosity of MetaCeram coatings as (vii) +e wear tests showed wear mechanisms due to a function of wear rate. adhesion, abrasion, and oxide formation, mainly. +ese mechanisms respond directly to the ductile agree with what was reported by Liyanage et al., who an- characteristics of nickel as the metallic matrix of the alyzed the abrasive wear resistance of Ni-WC coatings [25]. coatings and to the fragility of WC/Co ceramic, +ese authors found a close relationship between the which is the main aggregate in the MetaCeram microhardness and the wear resistance of the coatings; coating. In this work, it was possible to determine however, it is important to note that the wear rate is related the relationship of crystallographic properties of to both the overall hardness of the coatings, which is MetaCeram coatings, with their wear rate. Likewise, influenced by the average WC particle content in them and the influence of the topography of the coatings with the distribution of these particles on the surface. +e rate of the wear resistance was established. wear increases drastically when the mean free path between the WC particles exceeds 114 μm. +is is because a greater Data Availability distance between WC particles produces a significant fraction of the metallic Ni matrix on the surface of the wear +e data used to support the findings of this study are in- track in direct contact with abrasive sand particles [26–28]. cluded within the article. On the other hand, in the figure possibly a relationship between the wear rate and the porosity is not established, Conflicts of Interest since the values of the wear rate only show a notable change in coatings that have 0.42% porosity [29–31]. +e authors declare that they have no conflicts of interest. 4. Conclusions Acknowledgments MetaCeram coatings deposited as a function of the oxygen +e authors would like to thank COLCIENCIAS for pro- content of the flame on gray cast iron via spray fuse tech- viding financial support to the project “Caracterizacion ´ nique show the following characteristics. estructural y qu´ımica mediante haces de iones de recu- brimientos nanoestructurados con aplicaciones tecnolog- ´ (i) +e coatings exhibit values of microhardness close icas” and Universidad Nacional de Colombia. to the theoretical values, and the coatings deposited at a high rate of flow of the oxygen in the flame References exhibit the lowest microhardness. (ii) +e lowest oxygen content in the flame produced a [1] S. Purkayastha and D. K. 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Lima et al., “Effect of porosity on hardness of Al2O3-Y3Al5O12 ceramic composite,” http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png Advances in Tribology Hindawi Publishing Corporation

Tribological Behavior of Ni-Based WC-Co Coatings Deposited via Spray and Fuse Technique Varying the Oxygen Flow

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Hindawi Advances in Tribology Volume 2021, Article ID 8898349, 10 pages https://doi.org/10.1155/2021/8898349 Research Article Tribological Behavior of Ni-Based WC-Co Coatings Deposited via Spray and Fuse Technique Varying the Oxygen Flow 1,2 1 3 H. Jime´nez , J. J. Olaya , and J. E. Alfonso Department of Mechanical Engineering and Mechatronics, Universidad Nacional De Colombia, Street 45, 26-85, Bogota´, Colombia Research Group in Energy and Materials (REM), Faculty of Mechanical Engineering, Universidad Antonio Narino, Bogota, Colombia Ciencia De Materiales y Superficies, Physis Department, Universidad Nacional De Colombia, Street 45, 26-85, Bogota´, Colombia Correspondence should be addressed to J. E. Alfonso; jealfonsoo@unal.edu.co Received 10 May 2020; Accepted 24 March 2021; Published 20 May 2021 Academic Editor: João P. Davim Copyright © 2021 H. Jime´nez et al. +is is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. +e tribological behavior of Ni-based WC-Co coatings is analyzed. +e coatings were deposited on gray cast iron substrates in a spray and fuse process using SuperJet Eutalloy deposition equipment, varying the oxygen flow conditions in the flame. +e crystallographic structure of the coatings was characterized via the X-ray diffraction (XRD) technique. +e microhardness was measured on the surface and in cross sections of the coatings by means of a Knoop microhardness tester. +e topography and the morphological characteristics of the coatings and the tribo-surfaces were examined using scanning electron microscopy (SEM) and confocal microscopy, while the chemical composition was measured by means of energy-dispersive X-ray spectroscopy (EDS). +e tribological behavior of the coatings was examined via a cohesion-adhesion scratch test, using cross sections of the coatings. Furthermore, two wear tests were carried out, using the pin-on-disk method under ASTM G99 standard and an ASTM standard G65 sand/rubber wheel abrasion wear test. +e wear of the coatings showed a close relationship to the porosity in the metal matrix; since then, in the abrasive wear test, a high porosity is related with lower hardness in the coatings; likewise, a low hardness is related with a high wear. coatings have been used in applications such as protection 1. Introduction against abrasive wear for industrial tools [5, 6]. WC-Co coatings are frequently used in wear-resistance Some applications of the cermet coatings have been applications due to their tribological properties [1, 2]. reported by some authors like Szymanski ´ et al., who found +ese coatings have been deposited mainly using thermal that coatings produced by thermal spray techniques have spray techniques, such as high-velocity oil fuel (HVOF), shown high resistance to corrosion and erosion in industry arc spray, plasma spraying, and detonation spray coating applications. Cavitation erosion tests were performed on [3, 4]. +e spray and fuse thermal spray process has im- coatings deposited by the HBOF technique according with portant advantages compared to other thermal spray the ASTM G32 standard, identifying sliding wear mecha- techniques due to the ease of production of the coatings, nisms and cavitation in coatings. Likewise, failure analysis of the wide variety of geometries and surfaces that can be cermet coatings deposited by HBOF technique showed that coated, the relatively low cost of coating production, and Yttria reinforced WC-10Co4Cr coating has superior tribo- the ease of handling of the equipment. Furthermore, resistance and mechanical properties, while WC-10Co4Cr coatings produced using this technique have a lower de- coating showed good wear resistance in fly ash slurry which gree of porosity and high adhesion to the substrate. +ese possesses a weak acidic nature. +e mechanical properties of 2 Advances in Tribology the Ni-based alloy/nano-h-BN self-lubricating composite 600 s and 400 g of load using a steel ball of 838 HV of coatings were analyzing by Zhang et al., who found that the hardness and 10 mm in diameter and a test speed of 10 cm/s. average microhardness of the coatings was influenced by the Additionally, we used the ASTM G-65 test under the B addition of solid lubricant in the powder feedstocks [7–10]. procedure (130 N of load and 2000 revolutions of the wheel In the present investigation, we describe the tribological to obtain ∼1436 m of wear distance). behavior of Ni-based WC-Co coatings deposited via the spray and fuse technique and evaluate the tribological be- 3. Results and Discussion havior as a function of the oxygen flux. +e reports regarding the variation of the oxygen flow in thermal spray systems are 3.1. XRD Analysis. In a previous investigation [16], we found extensive, and authors such as Bandgopadhyag et al. and that the XRD pattern that corresponds to MetaCeram Nylen used computer software to model the effect of the powder exhibits Ni B and Ni peaks with Ni reflections in oxygen flow on the distribution of speeds and temperatures crystallographic planes (111), (200), (220), (311), and (222), in an oxyacetylene flame. +e heat power P dissipated by the according to the X’Pert HighScore card, with reference code: flame depends on the fuel/oxidant ratio and the fuel gas feed 03-065-2865. WC (hex) (001), (100), and (101), and W C and rate, mu; as the limiting factor in combustion is mO , it can metallic W peaks were detected, due to the decarburization process of the WC particles, according to the cards with be said that P is proportional to the oxygen flow. +erefore, the oxygen flow is a very important parameter in mechanical reference code 00-051-0939 and 01-070-2633. +is crystal- and tribological properties of the coatings grew via thermal lographic structure of the MetaCeram was reproduced in the spray technique; however, the reports found in the literature coatings produced under different oxygen flow conditions. in this regard are poor [11–15]. Additionally, in the coatings, a B O peak, with reflections in 2 3 crystallographic plane (310), appears in the patterns. +e crystallite size was determined using the Williamson–Hall 2. Experimental Setup method. Using the spray and fuse thermal spray technique, Ni-based WC-Co coatings were deposited on gray cast-iron cylin- 3.2. Microhardness. According to Paneto et al. [17], in order drical substrates of 41 mm in diameter and 4 mm in to calculate the theoretical hardness (HV ) of composite thickness, varying the oxygen flow in the oxyacetylene flame materials, such as MetaCeram coatings, it is necessary to four times, with the objective to obtain carburizing, neutral, consider the molar fractions of the deposited constituents and oxidizing flames. +e substrates were cleaned using a multiplied by their respective theoretical hardness. For commercial degreasing liquid and subsequently immersed in MetaCeram, the main elements of the flux powder are taken an ultrasonic bath for 10 minutes. A commercial powder as wt%, which are in the following order: Ni at 44%, WC/Co called MetaCeram was used for filler material. In the de- at 40%, and Cr at 9.3%. To calculate the theoretical hardness, position process of the coatings, the gray cast iron substrate the relationship used is, is preheated to temperatures between 500 and 600 C, then the filler material is sprayed onto the substrate, and then this HV � A630 􏼁 + B2050 􏼁 + C90 􏼁 , (1) 0 HV HV HV material is melted onto the substrate, forming the coating. +e deposition conditions are summarized in Table 1. +e where A is the molar fraction of Ni, B is the molar fraction of parameters of the pressure of the gases, the distance between WC, C is the molar fraction of Cr, 630 HV is the theoretical the spraying and fuse, and the nozzle type were given by the hardness of 100% dense Ni, 2050 HV is the theoretical manufaturater of MetaCeram powders. hardness of 100% dense WC/Co, and finally 90 HV is the +e crystalline structure of the coatings was analyzed theoretical hardness of 100% dense Cr. Using equation (1), using the X-ray diffraction (XRD) technique. +e XRD the theoretical hardness of the MetaCeram coatings was patterns were obtained with Panalytical equipment in calculated obtaining a value of 1105.57 HV10850 MPa. +is Bragg–Brentano geometry with Cu Kα radiation of value is very close to the average microhardness values ˚ ° λ � 1.5406 A and a step of 0.02 . To determine the crys- registered for the coatings in Table 2 for the coatings de- tallographic planes of the coatings, X´Pert HighScore soft- posited at different oxygen fluxes. +ese values are the result ware was used. Using scanning electron microscopy (SEM) of the average of the hardness taken on the diametric lines of and confocal laser microscopy, the morphology and the the surface of the coatings, with three control samples for topographical details of the coatings were analyzed, as well as each deposit. the wear tracks, in order to determine the wear mechanisms Figure 1 shows the variation in the microhardness with the crystallite size in the metallic Ni matrix and the WC/Co of the coatings. +e chemical analyses of the coatings and the wear tracks were carried out by means of energy-dispersive particles. +e graph shows that coatings with a crystallite size X-ray spectroscopy (EDS) using a FEI Quanta 200-r of 50 nm in the Ni matrix and 67 nm in the WC/Co matrix equipment. reach a maximum value of the microhardness. Additionally, a Microhardness measurements were carried out using a noticeable decrease in microhardness is also recorded for Knoop scale LECO micro indenter, with 300 g of load and crystallite values close to 10 nm, which is in accordance with 15 s of dwell time. +e wear measurement was made using the Hall–Petch theory which indicates that the yield stress and the ASTM G99-04 test, with a pin-on-disk CETR-UMT-2- hence the hardness are related with the inverse square root of 110 tester, working at room temperature, with a test time of crystallite size [18, 19]. Moreover, Sriraman et al. [20] report Advances in Tribology 3 Table 1: Deposition conditions of the MetaCeram coatings. Brand of torch SuperJet Eutalloy O pressure (psi) 39 (268.896 kPa) C H pressure (psi) 7 (48.2633 kPa) 2 2 O flow (SCFH) 11.04 12.88 14.72 16.56 C H flow (SCFH) 14.64 2 2 Powder code MetaCeram 23075 Powder composition 44Ni, 40WC/Co, 9.3Cr, 1.9 B, 2.1Fe, 2.3Si, 0.4 C. Spraying-fusion distance 150–20 mm Nozzle B2 Table 2: Average values of surface microhardness of MetaCeram coatings deposited at different oxygen fluxes. MetaCeram samples Average microhardness (MPa) +ickness (µm) Steel ball 8218± 94,31 Substrate 347.48± 54 - MetaCeram (theoretical value) 10850 - (11.04 SCFH) 9448.09± 32.15 228.41± 6.42 (12.88 SCFH) 10470.64± 61.23 230.53± 4.14 (14.72 SCFH) 10092.27± 12.95 270.14± 9.03 (16.56 SCFH) 9010.88± 67.65 250.16± 2.97 +e microhardness values summarized in Table 2 were made on the surface of the coatings since other values of the microhardness were made on the transversal section. 70 70 results obtained from the characterization carried out using the potentiodynamic polarization technique on the substrate and the coatings in a previous paper, and the average error in the 60 60 porosity measurement was 0.021% [16]. Figure 2 shows the cross section of the MetaCeram coatings; in this figure, the 50 50 pores of the coatings are clearly appreciated. Figure 3 shows the variation of the microhardness as a function of the porosity. It 40 40 is clear that large porosity values result in a decrease in the hardness of the deposits. +is behavior can be explained since 30 30 the load indenter did not find material in the porous places. 20 20 3.3. Scratch Test. Figure 4 shows the tracks for the scratch 8800 9000 9200 9400 9600 9800 1000010200 10400 10600 tests performed on the MetaCeram coatings for a load of Microhardness (MPa) 15 N. +e area of the cones was obtained via optical mi- Figure 1: Crystallite sizes of Ni matrix and WC-Co particles as a croscopy with image analyzer. +e scratch resistance values function of microhardness. obtained under the application of ISO/WD 27307 are summarized in Table 3. +e coefficient of variation (Vr) is determined according to, that refinement of the crystallite size of Ni W alloys results in an increase in the hardness of the material. As the micro- � ∗ 100%, (2) structure of the material is refined, the elastic limit or the hardness of the material increases and then decreases, after reaching a maximum yield stress threshold. Several studies where ρ represents the standard deviation and μ is the average value of the cone area [21, 22]. have established this threshold at values between 10 and 40 nm. +e effect of crystallite size on the tensile strength can In these coatings, the 5 N load did not generate a de- be analyzed from the theory of dislocation; thus, the plastic tectable scratch trace, due to their high hardness, while with deformation of the material must be able to overcome the a load of 10 N, although it was possible to appreciate the maximum stress, which increases the density of the dislo- scratch tracks and the formation of cones in the substrate- cations. A small crystallite size generates a greater number of coating interface and in the superficial zone, the propagation borders between crystals, and this hinders the movement of of cracks through the scratch pattern was not clearly seen. For the scratch tests performed with 15 N, the formation of a the dislocations, and the maximum tensile stress in a plastic deformation is strongly influenced by the average size of the cone at the substrate-coating interface as well as the surface of the cone was much clearer. +ese formations could crystallite and the morphology of the particle. +e reduction in microhardness is also highly influenced suggest that the failure in these coatings is both adhesive and cohesive. However, in the absence of clear cracking of the by porosity. +e porosity index was calculated through the Crystallite size Ni (nm) Crystallite size WC (nm) 4 Advances in Tribology Unmelted particles Pores Resign Coating Substrate HV Mag Sig WD 500.0µm Universidad Nacional de Colombia 25.0 kV 200× SE 8.7 mm Figure 2: MetaCeram coatings’ cross section. 0.15 0.20 0.25 0.30 0.35 0.40 0.45 Porosity (vol %) Figure 3: Microhardness vs porosity of MetaCeram coatings. substrate-coating interface, it can also be assumed that the were calculated according to equations (3) and (4), respectively. formation of the cone in the adhesive zone could be a +e worn volume calculation indicates that the coating did not product of the high hardness difference between the gray exhibit significant wear since wear occurs mainly on the pin cast iron substrate and the coating, which can cause an because the average hardness of the coating is greater than that abrupt change in the degree of penetration of the indenter of the pin. +is can be seen in Figure 6, which was taken with when passing from substrate to coating. confocal laser microscopy on the wear track. In the cohesive failure zone, the coating is separated by πD (3) V � , means of the scratch test for the 15 N load, and the release of 64d WC/Co particles or nonmolten particles was detected using where D represents the diameter of the pin and d is the the scratch test, which demonstrates that the carbide par- diameter of the wear track. ticles do not completely melt with the metallic Ni matrix of V 􏼐mm 􏼑 the coating. +e area of the cone was shown to be related to (4) K � , L(N)d(mm) the degree of porosity of the coatings: the coatings with a higher degree of porosity recorded higher values of the area where V is the worn volume and L is the load. of the cone of cohesive failure. In general, the coatings of MetaCeram showed that the wear coefficient K and the COF change appreciably at higher 3.4. Pin-on-Disk Wear Test. Figure 5 shows the friction co- oxygen flux in the flame. +is is probably due to the fact that efficient (COF) curves for the MetaCeram coatings deposited the products with a higher degree of hardness, such as WC/ under different oxygen flow conditions. +e COF of the Co, aggregate in the Ni matrix, which results in less effective coatings was obtained from the stable area of the graphs. By contact friction. +e results obtained in the adhesive wear means of optical microscopy using image analyzer, the average tests are in agreement with previous studies. Authors such as Torgerson et al. [23] report the formation of NiO layers in width of the wear tracks was obtained, in order to calculate the worn volume and the wear coefficient. Table 4 records the nickel-based coatings deposited via cold thermal spraying. +ese authors found that the formation of NiO layers re- parameters of the pin-on-disk test carried out on the Meta- Ceram coatings. +e worn volume and the wear coefficient duces the coefficient of friction. Likewise, WC particles Microhardness (MPa) Advances in Tribology 5 Figure 4: Scratch test of MetaCeram coatings. provided resistance to thermal softening and helped to +e images do not reveal furrows of abrasive wear; this improve the wear resistance at elevated temperatures. confirms that the wear mechanism for these coatings is Figure 7 shows the deterioration undergone by Meta- mainly due to adhesive wear produced by the oxides, evi- Ceram coatings in the course of the pin-on-disk wear test. denced by the XRD study and possible oxides formed during 16.6 SCFH 14.2 SCFH 12.8 SCFH 11.04 SCFH 6 Advances in Tribology Table 3: Average results of scratch resistance of MetaCeram coatings. Coating O flow (SCFH) Scratch test load (N) Projected cone area A (µm ) Variation coefficient Vr (%) Failure 2 c 5 — — - 11.04 10 9089.8 17.25 Adhesive/cohesive 15 11284 18.41 Adhesive/cohesive 5 — — - 12.88 10 3224.34 20.05 Adhesive/cohesive 15 6280.75 19.16 Adhesive/cohesive MetaCeram 5 — — - 14.72 10 1685.4 18.21 Adhesive/cohesive 15 1870.26 20.84 Adhesive/cohesive 5 — — - 16.56 10 8282 19.45 Adhesive/cohesive 15 17289 18.37 Adhesive/cohesive 0.7 0.6 0.5 0.4 0.3 0.2 0.1 100 200 300 400 500 600 Time (s) 11.04 (SCFH) 14.72 (SCFH) 12.88 (SCFH) 16.56 (SCFH) Figure 5: Coefficient of friction (COF) as a function of the time curves of MetaCeram coatings. Figure 6: Pin-on-disk wear tracks of MetaCeram coatings obtained by confocal microscopy. Table 4: Pin-on-disk test parameters of MetaCeram coatings. +e behavior of the wear rate as a function of the MetaCeram VW (MM3) K COF microhardness is illustrated in Figure 8. In the figure, it is (11.04 SCFH) 0.032± 0.061 8.03 E-8± 0,11 0.662± 0.022 evident that the wear coefficient increases with the (12.88 SCFH) 0.016± 0.037 1.05 E-8± 0,04 0.621± 0.013 microhardness. (14.72 SCFH) 0.025± 0.032 5,36 E-8± 0,23 0.423± 0.046 (16.56 SCFH) 0.054± 0.071 8.93 E-8± 0,07 0.675± 0.036 3.5. Abrasive Wear Test. +e abrasive wear tests of the gray cast substrates and the MetaCeram coatings were carried out the wear test. +e images also show that the WC particles do following procedure B of the ASTM G-65 rubber-wheel test not undergo significant deterioration after the wear test; on standard, which specifies a load of 130 N with 200-wheel the contrary, they act as accumulation points for worn revolutions, which generates 1436 m of wear distance using material, which prevents the abrasive wear mechanism. Ottawa sand as abrasive. Using Archard’s equation (equa- Some areas of the coatings showed microcracks at points tion (5)), the wear coefficient was calculated. For this, it was with defects such as nonmolten particles or pores on the necessary to determine the volume of worn material, which wear track. was obtained using equation (6). +e wear mechanism evident in the pink-on-disk test showed that the points, the contact between coating surface K∗ L∗ x V � , (5) and wear ball (contact points), are generate peaks or roughness own of the coatings deposited at high oxygen m − m pressure (16.56 SCFH). +e points of contact are broken and i f (6) V � (1000), regenerated as the test develops. Friction coefficient Advances in Tribology 7 Figure 7: SEM micrographs of pin-on-disk wear tracks of MetaCeram coatings. where K is the wear coefficient, V(mm ) is the wear volume Figure 9 shows the wear tracks of the MetaCeram of the softest material, H(GPa) is the hardness of the sample, coatings. It is possible to see the deterioration undergone by L(N) is the force exerted on the specimen, x(m) is the linear these coatings due to the abrasive wear tests. +e type of abrasion value, and mi and mf represent, respectively, the damage recorded was similar for all coatings, independent of initial and final values of the mass of the samples analyzed. the oxygen flow at which they were deposited. In the graphs, Metaceram 16.56 SCFH MetaCeram 14.72 SCFH Metaceram 12.88 SCFH MetaCeram 11.04 SCFH 8 Advances in Tribology 9000 9500 10000 10500 Microhardness (MPa) Figure 8: Microhardness vs wear coefficient of MetaCeram coatings. (a) (b) (c) Figure 9: SEM micrograph of wear traces for MetaCeram coatings. Co, following a line of fracture that borders these individual the presence of shallow grooves, a product of a micro- plowing mechanism, is evident. +ese furrows are produced structures, which allows us to infer a cohesion failure in by the displacement and later accumulation of the material them. It can also be seen how the fracture of these areas in front of the abrasive particles. +e particles of WC/Co in propagates to the metal matrix of the coating. +ese results the metallic Ni matrix of the MetaCeram coating act as are in agreement with those reported by St-Georges [24], accumulators of the detached material and even of the who found a mechanism of attrition by removal of the abrasive. +e accumulation of this material in specific zones metallic binder matrix in Ni-Cr + WC coatings, also re- can cause stress concentrations that lead to plastic defor- cording little evidence of fragmentation of WC particles. mation of the ductile areas of the coating, which are those Likewise, Liyanage et al. [25] recorded the phenomenon of where the concentration of Ni is predominant. +e mech- crack propagation for WC agglomerates in Ni-WC coatings. anism of microplowing is recorded in the graphs as dete- +e geometry of the cracking reported by these authors coincides with that reported in the present investigation. rioration zones 1 and 2, which are highlighted by circumference and rectangles; likewise, the zone where there Table 5 records the abrasive wear parameters obtained is plastic deformation is identified with the number 3 and is for MetaCeram coatings. +e results show a lower degree of highlighted with an oval. wear than the gray cast substrate. +is is due to the presence +e graphs also record the formation of microcracks, of the WC/Co system in the metallic Ni matrix in the mainly in areas rich in WC/Co. +is is due to the fragility of MetaCeram coatings. Both the wear rate and the wear co- the WC/Co particles and the high surface tension caused by efficient recorded showed a close relationship with the sliding of abrasive (sand) with these particles, which produce hardness and porosity of the coatings. Figure 10 shows the regions of acumulation, the abrasive and detached materials, variation of the microhardness as a function of the wear rate that increase the net pressure on the coating-substrate in- and the degree of porosity of the MetaCeram coatings. terphase. Figure 9(c) shows how the fracture occurs between +is graph shows a clear, decreasing relationship be- tween the microhardness and the wear rate. +ese results the individual grains that make up the regions rich in WC/ ∗ –8 3 ∗ Wear rate ( 10 mm /N mm) Advances in Tribology 9 Table 5: Gray cast iron substrate and MetaCeram coatings’ adhesive wear parameters. 3 −4 −5 3 Sample Mass loss (g) Worn volume (mm ) Wear coefficient K (×10 ) Wear rate W (×10 mm /Nm) MetaCeram (11.04 SCFH) 0.1238± 0,0048 13.601 3,441 3.6420 MetaCeram (12.88 SCFH) 0.0410± 0,0037 4.5064 1.218 1.2067 MetaCeram (14.72 SCFH) 0.0793± 0,0094 8.7133 2.443 2.3332 MetaCeram (16.56 SCFH) 0.1967± 0,0081 21.617 5.216 5.7885 (iii) +e porosity of the coatings increases with the 0.48 oxygen flow, which produces a decrease in their microhardness. 0.40 (iv) For all flows of oxygen used in the deposit of the 10000 coatings, cohesion and adhesion wear mechanisms 0.32 were simultaneously present. (v) In the stable zone of the coatings, the lowest COF 9500 was obtained in the coatings deposited with 14 0.24 SCFH oxygen flow. (vi) +e decarburization process negatively affected the 0.16 mechanical and tribological properties of Meta- Ceram coatings, both due to a reduction in hard- ness due to the degradation of WC in W C and 12 3 45 6 4 3 metallic W, as well as the increase in porosity due to Wear rate (×10 mm /Nm) the Kirkendall effect. Figure 10: Microhardness and porosity of MetaCeram coatings as (vii) +e wear tests showed wear mechanisms due to a function of wear rate. adhesion, abrasion, and oxide formation, mainly. +ese mechanisms respond directly to the ductile agree with what was reported by Liyanage et al., who an- characteristics of nickel as the metallic matrix of the alyzed the abrasive wear resistance of Ni-WC coatings [25]. coatings and to the fragility of WC/Co ceramic, +ese authors found a close relationship between the which is the main aggregate in the MetaCeram microhardness and the wear resistance of the coatings; coating. In this work, it was possible to determine however, it is important to note that the wear rate is related the relationship of crystallographic properties of to both the overall hardness of the coatings, which is MetaCeram coatings, with their wear rate. Likewise, influenced by the average WC particle content in them and the influence of the topography of the coatings with the distribution of these particles on the surface. +e rate of the wear resistance was established. wear increases drastically when the mean free path between the WC particles exceeds 114 μm. +is is because a greater Data Availability distance between WC particles produces a significant fraction of the metallic Ni matrix on the surface of the wear +e data used to support the findings of this study are in- track in direct contact with abrasive sand particles [26–28]. cluded within the article. On the other hand, in the figure possibly a relationship between the wear rate and the porosity is not established, Conflicts of Interest since the values of the wear rate only show a notable change in coatings that have 0.42% porosity [29–31]. +e authors declare that they have no conflicts of interest. 4. Conclusions Acknowledgments MetaCeram coatings deposited as a function of the oxygen +e authors would like to thank COLCIENCIAS for pro- content of the flame on gray cast iron via spray fuse tech- viding financial support to the project “Caracterizacion ´ nique show the following characteristics. estructural y qu´ımica mediante haces de iones de recu- brimientos nanoestructurados con aplicaciones tecnolog- ´ (i) +e coatings exhibit values of microhardness close icas” and Universidad Nacional de Colombia. to the theoretical values, and the coatings deposited at a high rate of flow of the oxygen in the flame References exhibit the lowest microhardness. (ii) +e lowest oxygen content in the flame produced a [1] S. Purkayastha and D. K. 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Advances in TribologyHindawi Publishing Corporation

Published: May 20, 2021

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