- Email: [email protected]
High temperature tribological studies of cold sprayed nickel based alloy on low carbon steels
Materials Today: Proceedings xxx (xxxx) xxx
Contents lists available at ScienceDirect
Materials Today: Proceedings journal homepage: www.elsevier.com/locate/matpr
High temperature tribological studies of cold sprayed nickel based alloy on low carbon steels B.V. Padmini a,⇑, Mahantayya Mathapati b, H.B. Niranjan a, P. Sampathkumaran a, S. Seetharamu c, M.R. Ramesh d, N. Mohan e a
Sambhram Institute of Technology, Bengaluru 560097, India K.L.E College of Engineering and Technology, Chikkodi, India Nitte Meenakshi Institute of Technology, Bengaluru, India d National Institute of Technology, Surathkal, India e Dr. Ambedkar Institute of Technology, Bengaluru, India b c
a r t i c l e
i n f o
Article history: Received 30 August 2019 Accepted 3 September 2019 Available online xxxx Keywords: Cold spray Super alloys High temperature Wear Microstructure Coatings
a b s t r a c t The boiler steels of grades SAE213 T11 and T22, find extensive applications in heat exchanger tubes, paper and pulp, chemical industries and refineries. Further, these steels are also used in shafts, cylinders, bearings, and in automotive transmission parts and these aspects are less explored. They experience low wear life in specific components, both at room and slightly higher temperature regimes. In order to protect them from these damages, coatings are deployed involving many techniques like HVOF, Plasma spray, Cold spray etc. so that the life of the components get extended. In cold spray coatings, the powders are fed at very high impact velocities of up to 1200 m/s on the substrate and undergo plastic deformation during the impact. There is no oxidation of the powder takes place during the process, as the coating is done at very less temperature and this is one of the lead characteristic of cold spray technique. This particular work mainly focuses on evaluating the tribological behaviour of nickel based super alloy powder on T11 and T22 low alloy steels by cold spray method, using pin on disc machine both at room temperature as well as at 200, 300 and 400 °C. The associated tests such as hardness, porosity, and microstructure have been undertaken to support the wear data. The wear damage assessment has been carried out using scanning electron microscope to arrive at the mechanism and also to give credence to the wear data. Ó 2019 Elsevier Ltd. All rights reserved. Selection and peer-review under responsibility of the scientific committee of the International conference on Materials and Manufacturing Methods.
1. Introduction The occurrence of surface related degradation of engineering components is on the increase leading to poor field performance. Among the surface modification methods, hard facing, spray deposition including thermal spray, detonation gun, PVD and CVD are some of the advanced methods followed. In spray deposition method, the surface properties are altered either by suitably varying the temperature or velocity [1]. Cold spray technique is one such advanced method and it overcomes the problems faced in thermal spray such as high temperature environment to prevent oxidation to occur, good dispersion of particles etc., while the coat⇑ Corresponding author.
ing is in progress. Micron sized (15–45 mm) particles in the solid state are impinged on the substrate and made adhere to the surface. Cold spray coating has an unique feature over the other conventional thermal spray processes wherein the powder used are not taken to the molten state but solidify at room temperature [2–5]. Nickel based alloys are well known for their stability, wear, erosion and corrosion resistance at room and high temperatures and are being used in turbines, boilers, cylinders, shafts dies, piston rings and conditions involving aggressive environments [6–8]. The Molybdenum based alloy helps in increasing the hardenability, toughness and heat resistance. Moreover, the application envisaged is for thermal power plant application to minimize, wear and corrosion problems especially in the boiler tubes. The other elements like Nb, Ta, Fe increases the strength of the alloy by precipitation hardening and thus imparts wear resistance at high
E-mail address: [email protected] (B.V. Padmini). https://doi.org/10.1016/j.matpr.2019.09.025 2214-7853/Ó 2019 Elsevier Ltd. All rights reserved. Selection and peer-review under responsibility of the scientific committee of the International conference on Materials and Manufacturing Methods.
Please cite this article as: B. V. Padmini, M. Mathapati, H. B. Niranjan et al., High temperature tribological studies of cold sprayed nickel based alloy on low carbon steels, Materials Today: Proceedings, https://doi.org/10.1016/j.matpr.2019.09.025
2
B.V. Padmini et al. / Materials Today: Proceedings xxx (xxxx) xxx
temperatures. Considering all these factors, it was thought that this combination would be the best choice and may work out to the advantage and they may be tried in the field as well. The performance of the coatings are not only ascertained by the composition, nature of the powder and the substrate but also on the coating microstructure which is determined by the type of coating technique along with the input process parameters adopted in the coating process [9–12]. Cold spray coating is a low temperature, solid state process and provides good adaptability to industries to choose the right type of substrate and parent material followed by optimization of the process parameters so that the end product performs satisfactory in the field especially in the tribological application. The cold spray process has the unique advantage of depositing sprayable powders at very high velocity and more over the process is done at room temperature. The deposition efficiency is much higher than other thermal spray processes such as plasma spray, HVOF, HVAF etc. The coatings are featured to possess good bond strength, as the adhesion to the substrate is quite good, low porosity levels and hardly any oxidation takes place. The thermal residual stress build up may be much less in the cold spray process than in the other cases. In the context of tribological behaviour, researchers have contributed to the various types of coating processes adopted involving numerous powders as well as feasible techniques followed by comprehensive evaluation methods to judge the performance. H S Sidhu et al. [13] studied the slide wear behaviour of HVOF coatings on T11 and T22 substrates by spraying them with Nickel Chromium and Stellite powders. The Stellite coatings have shown superior wear resistance than NiCr which is well supported by the light and SEM features. Chun Gho et al. [14] investigated the slide wear resistance of NiCrBSi and NiCrBSi/ WC-Ni coatings on stainless steel substrate by laser cladding process at elevated temperatures of 500. In this particular case, the samples were made to slide over Si3N4 base alloy. Among the materials studied, the NiCrBSi/ WC-Ni coatings have shown the best high temperature wear resistance. The mechanism of slide wear coupled with higher micro hardness, desired phases and other supporting microstructures have substantiated the wear and friction data. The Ni based hard faced deposits on stainless steel reported by D.Keshavan et al. [15] have been carried out using PTA welding process with a thickness of about 4–5 mm with the defect level being bare minimum. The slide-wear tests conducted on these samples at room temperature as well as at 573 K and 823 K, revealed that the wear resistance and coefficient of friction significantly reduced significantly with rise in temperature. The best wear resistance was obtained for 823 K. The hardness also showed an increasing trend with rise in temperature. Further, the wear mechanisms prevailed both at room and high temperatures are identified with proper reasoning to support the tribological data. In another work, the NiCrTiCRe powder coated on SAE213 T22 and SA516 G70 boiler steels using cold spray and HVOF process subjected to slide wear tests at room temperature reported [16] that the wear resistance greatly improved compared to bare T22 steels. As reported, the superior wear properties obtained in these coatings are mainly due higher hardness achieved. As this investigation concerns room temperature slide wear studies and not at elevated temperatures, the envisaged work gains importance from the point of assessing the wear behaviour at high temperatures. The substrate materials selection has been done based on the application. These substrates have the unique advantage of withstanding higher temperatures as they are already in use in super heater tubes in power plants. Thus, the creep resistance and corrosion properties in these materials are much higher compared to mild steel etc. The cost also comes in to picture and it is affordable. The main focus of this work is to study the high temperature dry sliding wear performance of nickel based alloy similar to the
composition of Inconel 625 coatings made on two grades of low carbon steels, by cold spray technique, as the information on this aspect is very less reported. The worn out surfaces are characterized by using Scanning Electron Microscopy (SEM) and EDAX. 2. Materials and methods 2.1. Materials selection The SAE 213 T11 and T22, low carbon boiler steels grades are selected as base alloy. The composition of the base alloy is analyzed using optical emission spectro-photo meter and it is given in the Table 1. The substrate material in the form of tube, are machined to plate form having dimensions 12 12 4 mm3. The commercially available feed stock material PG AMP 1060 equivalent to Inconel 625 of average particle size 5–25 m is used as the powder for spray deposition and its composition is given in Table 2. The powder morphology is studied using scanning electron microscope (SEM) and the same is shown in the Fig. 1. 2.2. Coating powders Cold Spray technique involves deposition of the powder on a substrate using PCS 1000 gun developed by M/s Plasma Giken, Japan. The substrates were grit blasted prior to spray deposition process for better adhesion of the coating. Helium is used as the carrier gas for the deposition of the coating. The pressure of the gas is maintained at 3 MPa and the temperature at 800 °C. The thickness of the coatings are measured using SEM. The porosity measurements of the coatings are determined using light microscopy with an image analyzer system attached to it. This is done based on ASTM standard [17]. The porosity is determined by studying the grey level indications in the analysis software. The average values of fifteen fields of are taken and the average value is reported. X-ray Diffraction equipment is used to analyze the phases in the powder and the coating. The micro-hardness of the coating and the substrate is measured across the cross section of the coated sample with a normal load of 200 g using a diamond indentor. 2.3. Sliding wear test The slide wear tests conducted is as per the guidelines in ASTM standard [18] using a pin on disc apparatus on a 12 12 4 mm3 flat surface, under dry conditions. The normal loads applied are 20 N, 30 N and 40 N and the test temperatures employed are 200 °C, 300 °C and 400 °C. The sliding speed adopted is 1.5 m/s at a sliding distance of 3000 m. The counter surface for sliding is an alloy steel disc with hardness 60 HRC and Ra of 0.2 m. The measurement of wear in terms of height change is recorded using an LVDT attached to the machine. Measurements are done on three representative samples and the average value is reported in case of wear and friction tests. The coefficient of friction is determined by dividing frictional load recorded in the friction monitor with the normal load. The worn surfaces are examined using SEM with an Energy Dispersive X-ray Analyzer (EDAX) attached to it, to interpret the wear data trends. 3. Results and discussion The substrates and coatings are designated as T11, T22, CT11 and CT22 respectively and these designations are used to display the results in the subsequent sections. The morphological studies of the powder and the as coated surface have been carried out using SEM and they are shown in the Figs. 1 and 2, respectively. The X Ray diffraction data of the powder for identifying the phases is shown in the Fig. 3. The surface roughness profile of the as
Please cite this article as: B. V. Padmini, M. Mathapati, H. B. Niranjan et al., High temperature tribological studies of cold sprayed nickel based alloy on low carbon steels, Materials Today: Proceedings, https://doi.org/10.1016/j.matpr.2019.09.025
3
B.V. Padmini et al. / Materials Today: Proceedings xxx (xxxx) xxx Table 1 Composition of the substrate. Sample Grade
C
Mn
Ph
S
Si
Cr
Mo
Fe
SAE 213 T11 SAE 213 T22
0.14 0.136
0.41 0.12
0.016 0.03
0.006 0.009
0.42 0.54
0.99 1.8
0.82 1.12
Balance Balance
Table 2 Composition of the powder (wt%). Powder Designation
Equivalent Commercial name
Nb
Fe
Mo
Cr
Ta
Ni
PG AMP 1060
Inconel 625
3.8
2
9.4
22
1
Balance
Fig. 1. SEM morphology of the powder.
Fig. 3. XRD data of the powder and T11 coating.
3.1. Coating powder characterization It is observed from Fig. 1 that the powder sample is having spherical shape and the particles are more or less uniformly distributed. The phase analysis data in Fig. 2 reveals the presence of the phase Ni3Cr2. The major peaks observed in respect of the phase are at 2h = 43.50°, 50.71°, 74.60° and 90.50° and they are in line with JCPDAS data. Major peaks of Ni-Cr solid solution (c-Ni3C2) is seen. Similar peaks are seen in both powder and coating, which infers that oxidation has not occurred during the cold spray process, as the oxide formed phase is not seen. This is the prerequisite for the development of wear resistant coatings in cold spray process. Fig. 2. SEM morphology of as sprayed coating on T11.
coated surface is shown in the Fig. 4. The Vickers hardness values of the substrates and the coatings are displayed in the Fig. 5. The photographs of the coating thickness and porosity measurement on CT11 and CT22 samples are shown in the Fig. 6a and b. The tribological data pertaining to wear rate and coefficient of friction for 200 °C, 300 °C and 400 °C at three different loads of 20 N, 30 N and 40 N respectively, are shown in the Figs. 7a–c and 8a–c, respectively. The SEM photographs of the CT11 samples, showing the tribological features after slide wear tests conducted at 400 °C and 200 °C, for a load of 40 N, at magnifications of 500 and 200 are displayed in the Figs. 9a and b and 10a and b, respectively. The SEM photographs of the T11 samples, showing the tribological features after slide wear tests conducted at 400 °C and 200 °C, for a load of 40 N, are shown in the Figs. 11a and b and 12a and b, respectively. The EDAX of the CT11 samples after wear at 400 °C and 200 °C are displayed in the Fig. 13a and b, respectively.
3.2. Surface characteristics of coatings The visual examination reveals that the as coated surface is quite smooth with grey appearance on it and hardly any cracks are noticed. The surface roughness measured was found to be 3.88 with a standard deviation of 0.617 mm and is shown in the Fig. 4. This value indicates that the surface is quite smooth. Further, the surface porosity levels found to be 0.032 for CT11 and 0.05% for CT22 samples. The porosity values are quite low and they reflect on the dense type of coatings obtained in the cold spray process. The dense coatings are obtained due to the good adherence of the particles during the impaction on the target material. The thickness of the CT11 coatings is 197 ± 20 m and that of CT22 is 190 ± 15 and is the average of four readings. Also, the hardness values support the surface properties especially the porosity levels. The hardness measured on the coating with T11 as the substrate is showing higher value compared to the coating made on T22. The reason for this may be attributed to
Please cite this article as: B. V. Padmini, M. Mathapati, H. B. Niranjan et al., High temperature tribological studies of cold sprayed nickel based alloy on low carbon steels, Materials Today: Proceedings, https://doi.org/10.1016/j.matpr.2019.09.025
4
B.V. Padmini et al. / Materials Today: Proceedings xxx (xxxx) xxx
Fig. 4. Roughness profile of the as coated surface.
Fig. 5. Micro vickers hardness of the samples.
the lower level of porosity obtained and dense type of coating obtained in T11. Even among the substrate material, T11 is showing higher hardness compared to T22. The high velocity collision of feedstock particles similar to micro shot peening of this unique coating technique and also the ramming effect during formation of the coating structure seems to be responsible for the increased hardness value of the substrate at the position adjacent to the first coating layer. Thus, similar trends in respect of hardness are noticed as in the case of coatings as well. 3.3. Slide wear and friction It is observed from the Fig. 7a–c that the wear rate has shown an increasing trend with increase in load application of 20 N, 30 N and 40 N respectively. This kind of behaviour is observed irrespective of the test temperature employed (RT 26 °C, 200, 300 and 400 °C). Further, it is seen that the wear rate of both the coatings are higher at 200 °C and least at 400 °C. It is also noticed that the wear rate increases from room temperature to 200 °C and drops down to a lower level at 300 °C and decreases further at 400 °C. The reason for higher wear rate at 200 °C in CT11 may be due to poor adhesion characteristics between the coating and the substrate interface. Also, there is an increase in debris formation and they are loosely attached causing abrasive wear. Hence the CT11
Fig. 6. a and b: Light microphotographs showing the coating thickness and porosity levels in CT11 and CT22.
shows higher wear rate. On the other hand, the debris formed in CT11 gets attached to the sample at 400 °C and providing a thin film. This has resulted in low wear rate. These trends are explained
Please cite this article as: B. V. Padmini, M. Mathapati, H. B. Niranjan et al., High temperature tribological studies of cold sprayed nickel based alloy on low carbon steels, Materials Today: Proceedings, https://doi.org/10.1016/j.matpr.2019.09.025
B.V. Padmini et al. / Materials Today: Proceedings xxx (xxxx) xxx
5
Fig. 8. a, b and c: Friction coefficient of T11, T22, CT11 and CT22 samples at a) 20 N b) 30 N and c) 40 N load.
Fig. 7. a, b and c: Wear rate of T11, T22, CT11, CT22 samples at a) 20 N b) 30 N and c) 40 N load.
based on the wear damage assessment using SEM, which is covered in the subsequent section. It is observed from the figures that the wear rate of the base materials T11 and T22 are much higher compared to their corresponding coated samples. The trend obtained in respect of the wear rate at 20 N load application repeats itself for the other loads as well. Between the two substrate materials, T11 is exhibiting higher wear resistance compared to T22 in view of higher hardness and lower porosity levels obtained. These hardness results are in agreement with the standard values reported.
As regards the coefficient of friction, it is seen that like in the case of wear rate, the friction coefficient increases from room temperature up to 200 °C and thereafter decreases. At 400 °C, the coefficient of friction of the coatings is showing the lowest value. The friction coefficient has decreased from 0.51 to 0.35 and thus there is a reduction in coefficient of friction value, which may be attributed to the increased debris formation and also they may act as solid lubricant in the form of thin film resulting in reducing the friction values. The coefficient of friction values are obtained in the range of 0.5 to 0.69 for T11 samples and 0.59 to 0.71 for T22 samples. The friction coefficients of the CT11 samples vary in the range of 0.32 to 0.52 and 0.35 to 0.6 for CT22 samples and are much lower compared to the parent samples. Now coming to the friction data obtained for load application of 20 N, 30 N and 40 N, it is least at 400 °C and highest at 200 °C. In the former case, the debris are not getting dislodged from the surface and they are adherent & soft providing a smooth surface, thus lowering the friction coefficient. In the latter case, the debris particles have come off
Please cite this article as: B. V. Padmini, M. Mathapati, H. B. Niranjan et al., High temperature tribological studies of cold sprayed nickel based alloy on low carbon steels, Materials Today: Proceedings, https://doi.org/10.1016/j.matpr.2019.09.025
6
B.V. Padmini et al. / Materials Today: Proceedings xxx (xxxx) xxx
Fig. 9. a and b SEM photographs of the worn surfaces of CT11 at 40 N load and 400 °C at a) 500 and b) 200.
Fig. 10. a and b: SEM photographs of the worn surfaces CT11 at 40 N load and 200 °C at a) 500 and b) 200.
Fig. 11. a and b:SEM photographs of the worn surfaces of T11 at 40 N load and 400 °C at a) 600 and b) 200.
and acts as abrasive media and providing more friction load, thus increasing the co-efficient of friction. Thus it is very well seen that both friction and wear go together irrespective of the temperature and load employed during the experiments. The high temperature wear studies conducted by Keshavan et al. [15] suggests that the hardness increased to a great extent improved the sliding wear resistance, with increase in tempera-
ture. Based on the worn surface features, the dominant wear mechanism was identified as severe abrasion and ploughing at RT and delamination of the layers at high temperature as well as tribo oxidation. The coefficient of friction also decreased with increase in temperature. Mrityunjaya Doddamani et al. [19] have studied the effect of composite coatings on the metallurgical and tribological properties and the deposition is made on MDN32 steel and the
Please cite this article as: B. V. Padmini, M. Mathapati, H. B. Niranjan et al., High temperature tribological studies of cold sprayed nickel based alloy on low carbon steels, Materials Today: Proceedings, https://doi.org/10.1016/j.matpr.2019.09.025
B.V. Padmini et al. / Materials Today: Proceedings xxx (xxxx) xxx
7
Fig. 12. a and b:SEM photographs of the worn surfaces of T11 at 40 N load and 200 °C at a) 600 and b) 200.
Fig. 13. a and b: EDAX data of CT11 at a) 400 °C and b) 200 °C.
Please cite this article as: B. V. Padmini, M. Mathapati, H. B. Niranjan et al., High temperature tribological studies of cold sprayed nickel based alloy on low carbon steels, Materials Today: Proceedings, https://doi.org/10.1016/j.matpr.2019.09.025
8
B.V. Padmini et al. / Materials Today: Proceedings xxx (xxxx) xxx
coating is subjected to sliding action at 20 N and 40 N load at RT, 200, 400 and 600 °C for evaluating the wear resistance and friction. From their findings, it is seen that the wear rate increased from RT to 400 °C, but decreased at 600 °C. Similar trends were seen in the coefficient of friction reported. Further, it is reported [19] that an elevation in the load from 20 N to 40 N results in higher wear rate as well as friction co-efficient of the coatings. All these data have been substantiated using SEM pictures wherein it is clearly seen that the phases formed on account of chemical reaction have beneficial effect on the properties as they act as abrasion particles in one case and solid lubricants in the other. In the present context, the work gains momentum from the point of enhancing the wear resistance and lowering of coefficient of friction for the NiCr based coatings produced by cold spray. Like in the above cases of reporting [15,19], the wear and friction have shown best properties at higher temperatures and the trends are in line with the published information. 3.4. Scanning electron microscopy It is very much evident from the surface topographical features that the pull out of the particles is noticed from the SEM photographs (Figs. 9a and b, 10a and b) for the wear test conducted at 40 N load for temperatures 400 °C and 200 °C. Further, it increases with increase in load. The degree of pull out does seem to depend on the magnitude of the load employed during the experiments. These reflect on the adhesion strength between the substrate and the coating material. It is observed that the deposition efficiency is lower as more particles after undergoing sliding wear get loosely bound to the substrate and acting as abrasive media at 200 °C, whereas at 400 °C, the debris particles come off due to adhesion mechanism. These observations are true for the load application of 20 N, 30 N and 40 N. The slide-wear damage of CT11 conducted at 200 °C (Fig. 10a and b) and 40 N load application reveals heavy debris formation with fragmentation of debris as well a few cracks are visible. The debris is masking the matrix as the matrix is in the state of highly disturbed and distorted condition. Further, ploughing marks as well as crater formation are observed in some regions. For the tests conducted at 400 °C and 40 N load, the SEM features (Fig. 9a and b) of CT11 show features like less debris formation, a few craters and shear of asperities in the form of sheets due to delamination of splats. The sliding wear debris obtained at 400 °C looks smaller in size compared to debris sizes formed at 200 °C. The Fig. 11a and b shows the SEM photographs of the worn surfaces of T11 samples at 400 °C. Deep Grooves are observed on the worn surfaces of the substrate owing to the wear damage between the sample surface, counter surface and debris, and material is removed by abrasive action. Similar deep grooves are also seen in the SEM photographs at 200 °C, as seen in the Fig. 12a and b. The EDAX images shown in the Fig. 13a, at 400 °C shows a higher percentage of oxygen content than the image shown in the Fig. 13b, at 200 °C. They are attributable due to the formation of oxide layers of Chromium, Molybdenum and Niobium and contributing to high wear resistance of the coatings at 400 °C. Thus the EDAX images shown, are a proof of the oxide formation like chromium oxide, molybdenum oxide, and niobium oxide thus forming wear resistant layers and reducing wear at higher temperatures. 4. Conclusions It is summarized that Nickel Chromium based alloy coating has been successfully made on T11 and T22 substrates from the point of studying the tribological properties at ambient as well as at 200 °C, 300 °C and 400 °C. The following inferences can be drawn.
1. The coatings CT11 and CT22 exhibit higher hardness compared to their corresponding substrate samples. The porosity of the coatings observed are very less hence proving the fact that dense coatings have been produced. 2. The wear rate of the coatings is much less compared to the substrates, irrespective of the load and temperature employed in the work. The reason may be attributed to the high hardness and low porosity obtained in these materials. 3. The slide wear rate irrespective of the load application shows maximum for the test conducted at 200 °C and thereafter it decreases at 300 °C and further reduces at 400 °C both for Ct11 and CT22. In fact the wear rate of CT11 is better by 3.21 times and CT22 is better by 3.16 times compared to T11 and T22, respectively. Among the coatings investigated, CT11 is exhibiting better wear resistance compared to CT22 at all loads and temperatures. 4. The data on coefficient of friction reveals that it increases with increase in temperature from room temperature to 200 °C and decreases thereafter. The friction coefficient of CT11 is decreased from 0.52 at 200 °C to 0.35 at 400 °C and that of CT22 samples from 0.6 to 0.37 respectively. For the substrate samples T11 and T22, the variation in the friction coefficient is marginal. 5. All these results get very good credence from hardness data, porosity levels, microstructural features such as EDAX, XRD, debris morphology, mechanism prevailed etc. 6. The CT11 and CT22 coatings, demonstrates that the adhesive wear situation with minimum grooves is prevailing at 400 °C and predominant abrasive action with deep grooves formation and delamination yielded at 200 °C. 7. The work summarizes the fact that cold spray is an innovative method of producing industrial coatings for superior wear resistance and low friction applications.
References [1] H. Singh, H. Khosla, Mater. Chem. Phys. 200 (2017) 57–69. [2] E. Irissou, J.G. Legoux, A.N. Ryabinin, B. Jodoin, C. Moreau, J. Therm. Spray Technol. 17 (4) (2008) 495–516. [3] J. Villafuerte, Met. Finish. 108 (1) (2010) 37–39. [4] S. Grigoriev, A. Okunkova, A. Sova, P. Bertrand, I. Smurov, Surf. Coat. Technol. 268 (2015) 77–84. [5] F. Gärtner, T. Stoltenhoff, T. Schmidt, H. Kreye, J. Therm. Spray Technol. 15 (2) (2006) 223–232. [6] C. Guo, J. Zhou, J. Chen, J. Zhao, Y. Yu, H. Zhou, Wear 270 (2011) 492–498. [7] J. Rodrıguez, A. Martın, R. Fernández, J.E. Fernández, Wear 255 (2003) 950–955. [8] K. Feng, Y. Chen, P. Deng, Y. Li, H. Zhao, F. Lu, Z. Li, J. Mater. Process. Technol. 243 (2017) 82–91. [9] V.K. Champagne, D. Helfritch, P. Leyman, S.B. Klotz, J. Therm. Spray Technol. 14 (3) (2005) 330–334. [10] C.J. Li, W.Y. Li, Y.Y. Wang, G.J. Yang, H. Fukanuma, Thin Solid Films 489 (1–2) (2005) 79–85. [11] R.S. Lima, A. Kucuk, C.C. Berndt, J. Karthikeyan, C.M. Kay, J. Lindemann, J. Mater. Sci. Lett. 21 (21) (2002) 1687–1689. [12] H. Singh, T.S. Sidhu, J. Karthikeyan, S.B.S. Kalsi, Surf. Coat. Technol. 261 (2015) 375–384. [13] H. Singh, B.S. Sidhu, S. Prakash, in: Materials Science Forum, Trans Tech Publications, 2012, pp. 21–29. [14] C. Guo, J. Zhou, J. Chen, J. Zhao, Y. Yu, H. Zhou, High temperature wear resistance of laser cladding NiCrBSi and NiCrBSi/WC-Ni composite coatings, Wear 270 (7–8) (2011) 492–498. [15] D. Kesavan, M. Kamaraj, Surf. Coat. Technol. 204 (24) (2010) 4034–4043. [16] Jasbir Singh, Harvinder Lal, Niraj Bala, Int. J. Mech. Eng. Robotics Res. 2278 (2013) 134–138. [17] ASTM E2109-01(2014), Standard Test Methods for Determining Area Percentage Porosity in Thermal Sprayed Coatings, ASTM International, West Conshohocken, PA, 2014. [18] ASTM G99-05, Standard Test Method for Wear Testing with a Pin-on-Disk Apparatus, ASTM International, West Conshohocken, PA, 2005. [19] M. Doddamani, M. Mathapati, M.R. Ramesh, Surf. Coat. Technol. 354 (2018) 92–100.
Please cite this article as: B. V. Padmini, M. Mathapati, H. B. Niranjan et al., High temperature tribological studies of cold sprayed nickel based alloy on low carbon steels, Materials Today: Proceedings, https://doi.org/10.1016/j.matpr.2019.09.025
Contents lists available at ScienceDirect
Materials Today: Proceedings journal homepage: www.elsevier.com/locate/matpr
High temperature tribological studies of cold sprayed nickel based alloy on low carbon steels B.V. Padmini a,⇑, Mahantayya Mathapati b, H.B. Niranjan a, P. Sampathkumaran a, S. Seetharamu c, M.R. Ramesh d, N. Mohan e a
Sambhram Institute of Technology, Bengaluru 560097, India K.L.E College of Engineering and Technology, Chikkodi, India Nitte Meenakshi Institute of Technology, Bengaluru, India d National Institute of Technology, Surathkal, India e Dr. Ambedkar Institute of Technology, Bengaluru, India b c
a r t i c l e
i n f o
Article history: Received 30 August 2019 Accepted 3 September 2019 Available online xxxx Keywords: Cold spray Super alloys High temperature Wear Microstructure Coatings
a b s t r a c t The boiler steels of grades SAE213 T11 and T22, find extensive applications in heat exchanger tubes, paper and pulp, chemical industries and refineries. Further, these steels are also used in shafts, cylinders, bearings, and in automotive transmission parts and these aspects are less explored. They experience low wear life in specific components, both at room and slightly higher temperature regimes. In order to protect them from these damages, coatings are deployed involving many techniques like HVOF, Plasma spray, Cold spray etc. so that the life of the components get extended. In cold spray coatings, the powders are fed at very high impact velocities of up to 1200 m/s on the substrate and undergo plastic deformation during the impact. There is no oxidation of the powder takes place during the process, as the coating is done at very less temperature and this is one of the lead characteristic of cold spray technique. This particular work mainly focuses on evaluating the tribological behaviour of nickel based super alloy powder on T11 and T22 low alloy steels by cold spray method, using pin on disc machine both at room temperature as well as at 200, 300 and 400 °C. The associated tests such as hardness, porosity, and microstructure have been undertaken to support the wear data. The wear damage assessment has been carried out using scanning electron microscope to arrive at the mechanism and also to give credence to the wear data. Ó 2019 Elsevier Ltd. All rights reserved. Selection and peer-review under responsibility of the scientific committee of the International conference on Materials and Manufacturing Methods.
1. Introduction The occurrence of surface related degradation of engineering components is on the increase leading to poor field performance. Among the surface modification methods, hard facing, spray deposition including thermal spray, detonation gun, PVD and CVD are some of the advanced methods followed. In spray deposition method, the surface properties are altered either by suitably varying the temperature or velocity [1]. Cold spray technique is one such advanced method and it overcomes the problems faced in thermal spray such as high temperature environment to prevent oxidation to occur, good dispersion of particles etc., while the coat⇑ Corresponding author.
ing is in progress. Micron sized (15–45 mm) particles in the solid state are impinged on the substrate and made adhere to the surface. Cold spray coating has an unique feature over the other conventional thermal spray processes wherein the powder used are not taken to the molten state but solidify at room temperature [2–5]. Nickel based alloys are well known for their stability, wear, erosion and corrosion resistance at room and high temperatures and are being used in turbines, boilers, cylinders, shafts dies, piston rings and conditions involving aggressive environments [6–8]. The Molybdenum based alloy helps in increasing the hardenability, toughness and heat resistance. Moreover, the application envisaged is for thermal power plant application to minimize, wear and corrosion problems especially in the boiler tubes. The other elements like Nb, Ta, Fe increases the strength of the alloy by precipitation hardening and thus imparts wear resistance at high
E-mail address: [email protected] (B.V. Padmini). https://doi.org/10.1016/j.matpr.2019.09.025 2214-7853/Ó 2019 Elsevier Ltd. All rights reserved. Selection and peer-review under responsibility of the scientific committee of the International conference on Materials and Manufacturing Methods.
Please cite this article as: B. V. Padmini, M. Mathapati, H. B. Niranjan et al., High temperature tribological studies of cold sprayed nickel based alloy on low carbon steels, Materials Today: Proceedings, https://doi.org/10.1016/j.matpr.2019.09.025
2
B.V. Padmini et al. / Materials Today: Proceedings xxx (xxxx) xxx
temperatures. Considering all these factors, it was thought that this combination would be the best choice and may work out to the advantage and they may be tried in the field as well. The performance of the coatings are not only ascertained by the composition, nature of the powder and the substrate but also on the coating microstructure which is determined by the type of coating technique along with the input process parameters adopted in the coating process [9–12]. Cold spray coating is a low temperature, solid state process and provides good adaptability to industries to choose the right type of substrate and parent material followed by optimization of the process parameters so that the end product performs satisfactory in the field especially in the tribological application. The cold spray process has the unique advantage of depositing sprayable powders at very high velocity and more over the process is done at room temperature. The deposition efficiency is much higher than other thermal spray processes such as plasma spray, HVOF, HVAF etc. The coatings are featured to possess good bond strength, as the adhesion to the substrate is quite good, low porosity levels and hardly any oxidation takes place. The thermal residual stress build up may be much less in the cold spray process than in the other cases. In the context of tribological behaviour, researchers have contributed to the various types of coating processes adopted involving numerous powders as well as feasible techniques followed by comprehensive evaluation methods to judge the performance. H S Sidhu et al. [13] studied the slide wear behaviour of HVOF coatings on T11 and T22 substrates by spraying them with Nickel Chromium and Stellite powders. The Stellite coatings have shown superior wear resistance than NiCr which is well supported by the light and SEM features. Chun Gho et al. [14] investigated the slide wear resistance of NiCrBSi and NiCrBSi/ WC-Ni coatings on stainless steel substrate by laser cladding process at elevated temperatures of 500. In this particular case, the samples were made to slide over Si3N4 base alloy. Among the materials studied, the NiCrBSi/ WC-Ni coatings have shown the best high temperature wear resistance. The mechanism of slide wear coupled with higher micro hardness, desired phases and other supporting microstructures have substantiated the wear and friction data. The Ni based hard faced deposits on stainless steel reported by D.Keshavan et al. [15] have been carried out using PTA welding process with a thickness of about 4–5 mm with the defect level being bare minimum. The slide-wear tests conducted on these samples at room temperature as well as at 573 K and 823 K, revealed that the wear resistance and coefficient of friction significantly reduced significantly with rise in temperature. The best wear resistance was obtained for 823 K. The hardness also showed an increasing trend with rise in temperature. Further, the wear mechanisms prevailed both at room and high temperatures are identified with proper reasoning to support the tribological data. In another work, the NiCrTiCRe powder coated on SAE213 T22 and SA516 G70 boiler steels using cold spray and HVOF process subjected to slide wear tests at room temperature reported [16] that the wear resistance greatly improved compared to bare T22 steels. As reported, the superior wear properties obtained in these coatings are mainly due higher hardness achieved. As this investigation concerns room temperature slide wear studies and not at elevated temperatures, the envisaged work gains importance from the point of assessing the wear behaviour at high temperatures. The substrate materials selection has been done based on the application. These substrates have the unique advantage of withstanding higher temperatures as they are already in use in super heater tubes in power plants. Thus, the creep resistance and corrosion properties in these materials are much higher compared to mild steel etc. The cost also comes in to picture and it is affordable. The main focus of this work is to study the high temperature dry sliding wear performance of nickel based alloy similar to the
composition of Inconel 625 coatings made on two grades of low carbon steels, by cold spray technique, as the information on this aspect is very less reported. The worn out surfaces are characterized by using Scanning Electron Microscopy (SEM) and EDAX. 2. Materials and methods 2.1. Materials selection The SAE 213 T11 and T22, low carbon boiler steels grades are selected as base alloy. The composition of the base alloy is analyzed using optical emission spectro-photo meter and it is given in the Table 1. The substrate material in the form of tube, are machined to plate form having dimensions 12 12 4 mm3. The commercially available feed stock material PG AMP 1060 equivalent to Inconel 625 of average particle size 5–25 m is used as the powder for spray deposition and its composition is given in Table 2. The powder morphology is studied using scanning electron microscope (SEM) and the same is shown in the Fig. 1. 2.2. Coating powders Cold Spray technique involves deposition of the powder on a substrate using PCS 1000 gun developed by M/s Plasma Giken, Japan. The substrates were grit blasted prior to spray deposition process for better adhesion of the coating. Helium is used as the carrier gas for the deposition of the coating. The pressure of the gas is maintained at 3 MPa and the temperature at 800 °C. The thickness of the coatings are measured using SEM. The porosity measurements of the coatings are determined using light microscopy with an image analyzer system attached to it. This is done based on ASTM standard [17]. The porosity is determined by studying the grey level indications in the analysis software. The average values of fifteen fields of are taken and the average value is reported. X-ray Diffraction equipment is used to analyze the phases in the powder and the coating. The micro-hardness of the coating and the substrate is measured across the cross section of the coated sample with a normal load of 200 g using a diamond indentor. 2.3. Sliding wear test The slide wear tests conducted is as per the guidelines in ASTM standard [18] using a pin on disc apparatus on a 12 12 4 mm3 flat surface, under dry conditions. The normal loads applied are 20 N, 30 N and 40 N and the test temperatures employed are 200 °C, 300 °C and 400 °C. The sliding speed adopted is 1.5 m/s at a sliding distance of 3000 m. The counter surface for sliding is an alloy steel disc with hardness 60 HRC and Ra of 0.2 m. The measurement of wear in terms of height change is recorded using an LVDT attached to the machine. Measurements are done on three representative samples and the average value is reported in case of wear and friction tests. The coefficient of friction is determined by dividing frictional load recorded in the friction monitor with the normal load. The worn surfaces are examined using SEM with an Energy Dispersive X-ray Analyzer (EDAX) attached to it, to interpret the wear data trends. 3. Results and discussion The substrates and coatings are designated as T11, T22, CT11 and CT22 respectively and these designations are used to display the results in the subsequent sections. The morphological studies of the powder and the as coated surface have been carried out using SEM and they are shown in the Figs. 1 and 2, respectively. The X Ray diffraction data of the powder for identifying the phases is shown in the Fig. 3. The surface roughness profile of the as
Please cite this article as: B. V. Padmini, M. Mathapati, H. B. Niranjan et al., High temperature tribological studies of cold sprayed nickel based alloy on low carbon steels, Materials Today: Proceedings, https://doi.org/10.1016/j.matpr.2019.09.025
3
B.V. Padmini et al. / Materials Today: Proceedings xxx (xxxx) xxx Table 1 Composition of the substrate. Sample Grade
C
Mn
Ph
S
Si
Cr
Mo
Fe
SAE 213 T11 SAE 213 T22
0.14 0.136
0.41 0.12
0.016 0.03
0.006 0.009
0.42 0.54
0.99 1.8
0.82 1.12
Balance Balance
Table 2 Composition of the powder (wt%). Powder Designation
Equivalent Commercial name
Nb
Fe
Mo
Cr
Ta
Ni
PG AMP 1060
Inconel 625
3.8
2
9.4
22
1
Balance
Fig. 1. SEM morphology of the powder.
Fig. 3. XRD data of the powder and T11 coating.
3.1. Coating powder characterization It is observed from Fig. 1 that the powder sample is having spherical shape and the particles are more or less uniformly distributed. The phase analysis data in Fig. 2 reveals the presence of the phase Ni3Cr2. The major peaks observed in respect of the phase are at 2h = 43.50°, 50.71°, 74.60° and 90.50° and they are in line with JCPDAS data. Major peaks of Ni-Cr solid solution (c-Ni3C2) is seen. Similar peaks are seen in both powder and coating, which infers that oxidation has not occurred during the cold spray process, as the oxide formed phase is not seen. This is the prerequisite for the development of wear resistant coatings in cold spray process. Fig. 2. SEM morphology of as sprayed coating on T11.
coated surface is shown in the Fig. 4. The Vickers hardness values of the substrates and the coatings are displayed in the Fig. 5. The photographs of the coating thickness and porosity measurement on CT11 and CT22 samples are shown in the Fig. 6a and b. The tribological data pertaining to wear rate and coefficient of friction for 200 °C, 300 °C and 400 °C at three different loads of 20 N, 30 N and 40 N respectively, are shown in the Figs. 7a–c and 8a–c, respectively. The SEM photographs of the CT11 samples, showing the tribological features after slide wear tests conducted at 400 °C and 200 °C, for a load of 40 N, at magnifications of 500 and 200 are displayed in the Figs. 9a and b and 10a and b, respectively. The SEM photographs of the T11 samples, showing the tribological features after slide wear tests conducted at 400 °C and 200 °C, for a load of 40 N, are shown in the Figs. 11a and b and 12a and b, respectively. The EDAX of the CT11 samples after wear at 400 °C and 200 °C are displayed in the Fig. 13a and b, respectively.
3.2. Surface characteristics of coatings The visual examination reveals that the as coated surface is quite smooth with grey appearance on it and hardly any cracks are noticed. The surface roughness measured was found to be 3.88 with a standard deviation of 0.617 mm and is shown in the Fig. 4. This value indicates that the surface is quite smooth. Further, the surface porosity levels found to be 0.032 for CT11 and 0.05% for CT22 samples. The porosity values are quite low and they reflect on the dense type of coatings obtained in the cold spray process. The dense coatings are obtained due to the good adherence of the particles during the impaction on the target material. The thickness of the CT11 coatings is 197 ± 20 m and that of CT22 is 190 ± 15 and is the average of four readings. Also, the hardness values support the surface properties especially the porosity levels. The hardness measured on the coating with T11 as the substrate is showing higher value compared to the coating made on T22. The reason for this may be attributed to
Please cite this article as: B. V. Padmini, M. Mathapati, H. B. Niranjan et al., High temperature tribological studies of cold sprayed nickel based alloy on low carbon steels, Materials Today: Proceedings, https://doi.org/10.1016/j.matpr.2019.09.025
4
B.V. Padmini et al. / Materials Today: Proceedings xxx (xxxx) xxx
Fig. 4. Roughness profile of the as coated surface.
Fig. 5. Micro vickers hardness of the samples.
the lower level of porosity obtained and dense type of coating obtained in T11. Even among the substrate material, T11 is showing higher hardness compared to T22. The high velocity collision of feedstock particles similar to micro shot peening of this unique coating technique and also the ramming effect during formation of the coating structure seems to be responsible for the increased hardness value of the substrate at the position adjacent to the first coating layer. Thus, similar trends in respect of hardness are noticed as in the case of coatings as well. 3.3. Slide wear and friction It is observed from the Fig. 7a–c that the wear rate has shown an increasing trend with increase in load application of 20 N, 30 N and 40 N respectively. This kind of behaviour is observed irrespective of the test temperature employed (RT 26 °C, 200, 300 and 400 °C). Further, it is seen that the wear rate of both the coatings are higher at 200 °C and least at 400 °C. It is also noticed that the wear rate increases from room temperature to 200 °C and drops down to a lower level at 300 °C and decreases further at 400 °C. The reason for higher wear rate at 200 °C in CT11 may be due to poor adhesion characteristics between the coating and the substrate interface. Also, there is an increase in debris formation and they are loosely attached causing abrasive wear. Hence the CT11
Fig. 6. a and b: Light microphotographs showing the coating thickness and porosity levels in CT11 and CT22.
shows higher wear rate. On the other hand, the debris formed in CT11 gets attached to the sample at 400 °C and providing a thin film. This has resulted in low wear rate. These trends are explained
Please cite this article as: B. V. Padmini, M. Mathapati, H. B. Niranjan et al., High temperature tribological studies of cold sprayed nickel based alloy on low carbon steels, Materials Today: Proceedings, https://doi.org/10.1016/j.matpr.2019.09.025
B.V. Padmini et al. / Materials Today: Proceedings xxx (xxxx) xxx
5
Fig. 8. a, b and c: Friction coefficient of T11, T22, CT11 and CT22 samples at a) 20 N b) 30 N and c) 40 N load.
Fig. 7. a, b and c: Wear rate of T11, T22, CT11, CT22 samples at a) 20 N b) 30 N and c) 40 N load.
based on the wear damage assessment using SEM, which is covered in the subsequent section. It is observed from the figures that the wear rate of the base materials T11 and T22 are much higher compared to their corresponding coated samples. The trend obtained in respect of the wear rate at 20 N load application repeats itself for the other loads as well. Between the two substrate materials, T11 is exhibiting higher wear resistance compared to T22 in view of higher hardness and lower porosity levels obtained. These hardness results are in agreement with the standard values reported.
As regards the coefficient of friction, it is seen that like in the case of wear rate, the friction coefficient increases from room temperature up to 200 °C and thereafter decreases. At 400 °C, the coefficient of friction of the coatings is showing the lowest value. The friction coefficient has decreased from 0.51 to 0.35 and thus there is a reduction in coefficient of friction value, which may be attributed to the increased debris formation and also they may act as solid lubricant in the form of thin film resulting in reducing the friction values. The coefficient of friction values are obtained in the range of 0.5 to 0.69 for T11 samples and 0.59 to 0.71 for T22 samples. The friction coefficients of the CT11 samples vary in the range of 0.32 to 0.52 and 0.35 to 0.6 for CT22 samples and are much lower compared to the parent samples. Now coming to the friction data obtained for load application of 20 N, 30 N and 40 N, it is least at 400 °C and highest at 200 °C. In the former case, the debris are not getting dislodged from the surface and they are adherent & soft providing a smooth surface, thus lowering the friction coefficient. In the latter case, the debris particles have come off
Please cite this article as: B. V. Padmini, M. Mathapati, H. B. Niranjan et al., High temperature tribological studies of cold sprayed nickel based alloy on low carbon steels, Materials Today: Proceedings, https://doi.org/10.1016/j.matpr.2019.09.025
6
B.V. Padmini et al. / Materials Today: Proceedings xxx (xxxx) xxx
Fig. 9. a and b SEM photographs of the worn surfaces of CT11 at 40 N load and 400 °C at a) 500 and b) 200.
Fig. 10. a and b: SEM photographs of the worn surfaces CT11 at 40 N load and 200 °C at a) 500 and b) 200.
Fig. 11. a and b:SEM photographs of the worn surfaces of T11 at 40 N load and 400 °C at a) 600 and b) 200.
and acts as abrasive media and providing more friction load, thus increasing the co-efficient of friction. Thus it is very well seen that both friction and wear go together irrespective of the temperature and load employed during the experiments. The high temperature wear studies conducted by Keshavan et al. [15] suggests that the hardness increased to a great extent improved the sliding wear resistance, with increase in tempera-
ture. Based on the worn surface features, the dominant wear mechanism was identified as severe abrasion and ploughing at RT and delamination of the layers at high temperature as well as tribo oxidation. The coefficient of friction also decreased with increase in temperature. Mrityunjaya Doddamani et al. [19] have studied the effect of composite coatings on the metallurgical and tribological properties and the deposition is made on MDN32 steel and the
Please cite this article as: B. V. Padmini, M. Mathapati, H. B. Niranjan et al., High temperature tribological studies of cold sprayed nickel based alloy on low carbon steels, Materials Today: Proceedings, https://doi.org/10.1016/j.matpr.2019.09.025
B.V. Padmini et al. / Materials Today: Proceedings xxx (xxxx) xxx
7
Fig. 12. a and b:SEM photographs of the worn surfaces of T11 at 40 N load and 200 °C at a) 600 and b) 200.
Fig. 13. a and b: EDAX data of CT11 at a) 400 °C and b) 200 °C.
Please cite this article as: B. V. Padmini, M. Mathapati, H. B. Niranjan et al., High temperature tribological studies of cold sprayed nickel based alloy on low carbon steels, Materials Today: Proceedings, https://doi.org/10.1016/j.matpr.2019.09.025
8
B.V. Padmini et al. / Materials Today: Proceedings xxx (xxxx) xxx
coating is subjected to sliding action at 20 N and 40 N load at RT, 200, 400 and 600 °C for evaluating the wear resistance and friction. From their findings, it is seen that the wear rate increased from RT to 400 °C, but decreased at 600 °C. Similar trends were seen in the coefficient of friction reported. Further, it is reported [19] that an elevation in the load from 20 N to 40 N results in higher wear rate as well as friction co-efficient of the coatings. All these data have been substantiated using SEM pictures wherein it is clearly seen that the phases formed on account of chemical reaction have beneficial effect on the properties as they act as abrasion particles in one case and solid lubricants in the other. In the present context, the work gains momentum from the point of enhancing the wear resistance and lowering of coefficient of friction for the NiCr based coatings produced by cold spray. Like in the above cases of reporting [15,19], the wear and friction have shown best properties at higher temperatures and the trends are in line with the published information. 3.4. Scanning electron microscopy It is very much evident from the surface topographical features that the pull out of the particles is noticed from the SEM photographs (Figs. 9a and b, 10a and b) for the wear test conducted at 40 N load for temperatures 400 °C and 200 °C. Further, it increases with increase in load. The degree of pull out does seem to depend on the magnitude of the load employed during the experiments. These reflect on the adhesion strength between the substrate and the coating material. It is observed that the deposition efficiency is lower as more particles after undergoing sliding wear get loosely bound to the substrate and acting as abrasive media at 200 °C, whereas at 400 °C, the debris particles come off due to adhesion mechanism. These observations are true for the load application of 20 N, 30 N and 40 N. The slide-wear damage of CT11 conducted at 200 °C (Fig. 10a and b) and 40 N load application reveals heavy debris formation with fragmentation of debris as well a few cracks are visible. The debris is masking the matrix as the matrix is in the state of highly disturbed and distorted condition. Further, ploughing marks as well as crater formation are observed in some regions. For the tests conducted at 400 °C and 40 N load, the SEM features (Fig. 9a and b) of CT11 show features like less debris formation, a few craters and shear of asperities in the form of sheets due to delamination of splats. The sliding wear debris obtained at 400 °C looks smaller in size compared to debris sizes formed at 200 °C. The Fig. 11a and b shows the SEM photographs of the worn surfaces of T11 samples at 400 °C. Deep Grooves are observed on the worn surfaces of the substrate owing to the wear damage between the sample surface, counter surface and debris, and material is removed by abrasive action. Similar deep grooves are also seen in the SEM photographs at 200 °C, as seen in the Fig. 12a and b. The EDAX images shown in the Fig. 13a, at 400 °C shows a higher percentage of oxygen content than the image shown in the Fig. 13b, at 200 °C. They are attributable due to the formation of oxide layers of Chromium, Molybdenum and Niobium and contributing to high wear resistance of the coatings at 400 °C. Thus the EDAX images shown, are a proof of the oxide formation like chromium oxide, molybdenum oxide, and niobium oxide thus forming wear resistant layers and reducing wear at higher temperatures. 4. Conclusions It is summarized that Nickel Chromium based alloy coating has been successfully made on T11 and T22 substrates from the point of studying the tribological properties at ambient as well as at 200 °C, 300 °C and 400 °C. The following inferences can be drawn.
1. The coatings CT11 and CT22 exhibit higher hardness compared to their corresponding substrate samples. The porosity of the coatings observed are very less hence proving the fact that dense coatings have been produced. 2. The wear rate of the coatings is much less compared to the substrates, irrespective of the load and temperature employed in the work. The reason may be attributed to the high hardness and low porosity obtained in these materials. 3. The slide wear rate irrespective of the load application shows maximum for the test conducted at 200 °C and thereafter it decreases at 300 °C and further reduces at 400 °C both for Ct11 and CT22. In fact the wear rate of CT11 is better by 3.21 times and CT22 is better by 3.16 times compared to T11 and T22, respectively. Among the coatings investigated, CT11 is exhibiting better wear resistance compared to CT22 at all loads and temperatures. 4. The data on coefficient of friction reveals that it increases with increase in temperature from room temperature to 200 °C and decreases thereafter. The friction coefficient of CT11 is decreased from 0.52 at 200 °C to 0.35 at 400 °C and that of CT22 samples from 0.6 to 0.37 respectively. For the substrate samples T11 and T22, the variation in the friction coefficient is marginal. 5. All these results get very good credence from hardness data, porosity levels, microstructural features such as EDAX, XRD, debris morphology, mechanism prevailed etc. 6. The CT11 and CT22 coatings, demonstrates that the adhesive wear situation with minimum grooves is prevailing at 400 °C and predominant abrasive action with deep grooves formation and delamination yielded at 200 °C. 7. The work summarizes the fact that cold spray is an innovative method of producing industrial coatings for superior wear resistance and low friction applications.
References [1] H. Singh, H. Khosla, Mater. Chem. Phys. 200 (2017) 57–69. [2] E. Irissou, J.G. Legoux, A.N. Ryabinin, B. Jodoin, C. Moreau, J. Therm. Spray Technol. 17 (4) (2008) 495–516. [3] J. Villafuerte, Met. Finish. 108 (1) (2010) 37–39. [4] S. Grigoriev, A. Okunkova, A. Sova, P. Bertrand, I. Smurov, Surf. Coat. Technol. 268 (2015) 77–84. [5] F. Gärtner, T. Stoltenhoff, T. Schmidt, H. Kreye, J. Therm. Spray Technol. 15 (2) (2006) 223–232. [6] C. Guo, J. Zhou, J. Chen, J. Zhao, Y. Yu, H. Zhou, Wear 270 (2011) 492–498. [7] J. Rodrıguez, A. Martın, R. Fernández, J.E. Fernández, Wear 255 (2003) 950–955. [8] K. Feng, Y. Chen, P. Deng, Y. Li, H. Zhao, F. Lu, Z. Li, J. Mater. Process. Technol. 243 (2017) 82–91. [9] V.K. Champagne, D. Helfritch, P. Leyman, S.B. Klotz, J. Therm. Spray Technol. 14 (3) (2005) 330–334. [10] C.J. Li, W.Y. Li, Y.Y. Wang, G.J. Yang, H. Fukanuma, Thin Solid Films 489 (1–2) (2005) 79–85. [11] R.S. Lima, A. Kucuk, C.C. Berndt, J. Karthikeyan, C.M. Kay, J. Lindemann, J. Mater. Sci. Lett. 21 (21) (2002) 1687–1689. [12] H. Singh, T.S. Sidhu, J. Karthikeyan, S.B.S. Kalsi, Surf. Coat. Technol. 261 (2015) 375–384. [13] H. Singh, B.S. Sidhu, S. Prakash, in: Materials Science Forum, Trans Tech Publications, 2012, pp. 21–29. [14] C. Guo, J. Zhou, J. Chen, J. Zhao, Y. Yu, H. Zhou, High temperature wear resistance of laser cladding NiCrBSi and NiCrBSi/WC-Ni composite coatings, Wear 270 (7–8) (2011) 492–498. [15] D. Kesavan, M. Kamaraj, Surf. Coat. Technol. 204 (24) (2010) 4034–4043. [16] Jasbir Singh, Harvinder Lal, Niraj Bala, Int. J. Mech. Eng. Robotics Res. 2278 (2013) 134–138. [17] ASTM E2109-01(2014), Standard Test Methods for Determining Area Percentage Porosity in Thermal Sprayed Coatings, ASTM International, West Conshohocken, PA, 2014. [18] ASTM G99-05, Standard Test Method for Wear Testing with a Pin-on-Disk Apparatus, ASTM International, West Conshohocken, PA, 2005. [19] M. Doddamani, M. Mathapati, M.R. Ramesh, Surf. Coat. Technol. 354 (2018) 92–100.
Please cite this article as: B. V. Padmini, M. Mathapati, H. B. Niranjan et al., High temperature tribological studies of cold sprayed nickel based alloy on low carbon steels, Materials Today: Proceedings, https://doi.org/10.1016/j.matpr.2019.09.025