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Effect of heat treatment on structure and property evolutions of atmospheric plasma sprayed NiCrBSi coatings
Surface & Coatings Technology 325 (2017) 548–554
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Surface & Coatings Technology journal homepage: www.elsevier.com/locate/surfcoat
Effect of heat treatment on structure and property evolutions of atmospheric plasma sprayed NiCrBSi coatings Liming Liu a, Haifeng Xu a, Jinkun Xiao a, Xinlong Wei a, Ga Zhang b, Chao Zhang a,⁎ a b
College of Mechanical Engineering, Yangzhou University, Yangzhou 225127, China State Key Laboratory of Solid Lubrication, Lanzhou Institute of Chemical Physics, Chinese Academy of Sciences, Lanzhou 730000, China
a r t i c l e
i n f o
Article history: Received 8 May 2017 Revised 30 June 2017 Accepted in revised form 3 July 2017 Available online 04 July 2017 Keywords: Plasma spray NiCrBSi coating Heat treatment Microstructure Wear resistance
a b s t r a c t To investigate the evolutions of structures and properties of NiCrBSi coatings on cylinder liner of engines during its service, atmospheric plasma sprayed (APS) NiCrBSi coatings were heat treated at 300, 500, or 700 °C in this work. The effect of heat treatment on microstructure, phase composition, microhardness and tribological performance has been investigated. It was identified that as-sprayed coatings mainly consisted of γ-(Ni, Fe) phase while CrB and Ni3B phases precipitated from the coatings during the heat treatments at 500 and 700 °C. In addition, inter-splat oxidation of the coating during the heat treatment occurred. Moreover, the crystallinity of the coating was significantly enhanced with increasing the heat treatment temperature. The heat treatment improved obviously the microhardness whereas it did not exert a pronounced effect on the friction coefficients of the coatings. In spite of the enhanced microhardness, the heat treatment at 700 °C increased the wear rate comparatively. It was revealed that inter-splat debonding of the coating surface layer involved in the friction dominated the wear resistance of the coating. Inter-splat oxidation and reduction of coating toughness due to heat treatment can account for the increased wear rate. © 2017 Elsevier B.V. All rights reserved.
1. Introduction Nickel-based alloys are widely applied for corrosion and wear resistant application. NiCrBSi is a self-fluxing alloy, and the presence of B and Si not only enhances the self-fluxing property of the metal which is favorable for coating deposition but also forms hard phase with Ni, such as Ni3B [1,2]. In addition, chromium can further improve its corrosion and wear resistance through the precipitation of hard particles [3]. Thermally sprayed NiCrBSi coatings are currently considered to be a potential substitute of conventional electroplating hard chromium layer applied for cylinder liner of diesel engine [4]. The most important set of components in modern engines is cylinder unit, which accounts for about half of the total frictional loss [5,6]. A typical material used for cylinder liner of the diesel engine is casting iron. However, for long-term applications, utilization of cast iron showed obvious disadvantages, such as high power consumption, low wear resistance, easy to corrosion, low fuel efficiency and incomplete combustion, etc. [7]. Plasma spraying has been identified in recent years as a promising solution to deposit protection coatings on cylinder liners for enhancing their lifetime [8,9]. However, coating delamination may occur due to
⁎ Corresponding author. E-mail addresses: [email protected], [email protected] (C. Zhang).
http://dx.doi.org/10.1016/j.surfcoat.2017.07.011 0257-8972/© 2017 Elsevier B.V. All rights reserved.
residual stress in the coating and unmatched elastic modulus, distinct thermal expansion coefficients between the coating and substrate [10–12]. Moreover, cracks, pores, oxides and unmelted particles are usually inevitable in plasma-sprayed coatings, which can lower the tribological performance [13–15]. On the other hand, plasma spraying is a rapid melting and solidification process, and thus numerous amorphous phases readily form in as-sprayed coatings. Previous works have reported that nickel-based thermally sprayed coatings containing amorphous structures exhibit high hardness and wear-corrosion resistance [16,17]. Nevertheless, the amorphous structures are metastable, and therefore recrystallization may occur when the coatings are exposed to high-temperature conditions during its service. As known that the service temperature of water cool cylinder liner is in a range of 300–500 °C. Hence, the precipitated grains in the deposited coating can evolve during its service, which can exert an influence on the hardness and wear resistance. That is, the structure and performance of the coating can vary as a function of service time and temperature. Post heat treatment is usually helpful for getting a dense coating with high cohesion and adhesion strengths [18]. Bergant et al. [19,20] investigated the effects of heat treatment and remelting on the quality of flame sprayed NiCrBSi coatings, and the authors demonstrated that the adhesion between coating and substrate after a 930 °C heat treatment was obviously enhanced. Moreover, denser NiCrBSi coatings with a homogeneous microstructure, low porosity and low residual stress were achieved by 5-minute remelting treatment. Li et al. [21]
L. Liu et al. / Surface & Coatings Technology 325 (2017) 548–554 Table 1 Chemical composition of NiCrBSi powders.
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Table 2 Selected plasma spraying parameters.
Element
Ni
Cr
B
Si
Fe
C
Parameters
Values
wt%
Bal.
17.53
3.27
4.01
4.43
0.82
Primary gas, Ar (L/min) Secondary gas, H2 (L/min) Plasma current (A) Plasma voltage (V) Powder feed rate (g/min) Spraying distance (mm) Gun translation velocity (mm/s)
55 7.5 516 64 60 140 200
studied the influence of heat treatment on microstructure and mechanical properties of NiCrBSi/WC coatings. Their results showed that the heat treatment at 900 °C for 1 h not only improved the hardness and fracture toughness but also reduced the wear rate, frictions coefficient and cracking susceptibility of the coatings. Lu et al. [22] analyzed the effects of heat treatment at 600 °C on microstructure and mechanical properties of laser cladded Ni60/h-BN self-lubricating composite coatings, and they disclosed that the residual stress in the coating was relieved after the heat treatment. In addition, the microhardness and elastic modulus of the coatings were enhanced in comparison to those of the as-cladded coatings. The heat treatment at 600 °C for 1 h showed the best wear resistance. Nevertheless, most of the previously works were limited to high temperature heat treatment and even remelting of NiCrBSi based coatings. The results are not enough to elucidate the evolution of coating microstructure and properties under real working conditions of the cylinder liner. The aim of this work was to study the effect of service temperature on microstructure evolution and tribological properties of atmospheric plasma-sprayed NiCrBSi coatings. Taking into account the service temperature of atmospheric plasma-sprayed NiCrBSi coatings in cylinder liners, the heat treatments at 300, 500, and 700 °C for 1 h were adopted in this work. The microstructure, phase composition and microhardness of as-sprayed and heat treated coatings were characterized. The tribological properties of the as-sprayed and heat treated coatings were examined. The wear mechanisms of the coatings were investigated.
2. Experimental procedure 2.1. Sample preparation Commercially available gas atomized NiCrBSi powders with a particle size ranging from 40 to 60 μm were chosen as feedstock materials. The composition of the powders was listed in Table 1. As seen from Fig. 1, the powders present a spherical shape which is beneficial to get good fluidity during plasma spraying process. 304 stainless steel plates (size: 60 mm × 40 mm × 3 mm) were used as substrates. Prior to spraying, the substrates were grit blasted by 24 mesh brown corundum to activate the surface. The coating deposition was carried out using an F4MB-XL plasma gun (Oerlikon Metco, Switzerland). A six-axis robot manipulator (ABB, Sweden) was used to get a uniform movement of the plasma gun. The
optimized spraying parameters were given in Table 2. The feedstock material was injected vertically into the plasma torch by Ar carrier gas. To reduce the substrate temperature, compressed air was placed at the back of the substrates at a pressure of 0.3 MPa as cooling gas. The as-sprayed coatings had a thickness of approximately 350 μm. After deposition, the coatings were cut into small specimens by a cutting machine for heat treatment and further analysis. Coated specimens were buried in a crucible filled with alumina powders to ensure the uniform heating. The heat treatments at 300, 500, or 700 °C were carried out in a muffle furnace with a heating rate of 10 °C/min. After reaching the set temperature and keep for 1 h, the specimens were removed from the furnace and cooled in air subsequently. 2.2. Coating characterization Ten specimens for each condition were prepared to analyze the microstructure and porosity of the coatings [23]. The cross-sectional morphologies of the as-sprayed and heat treated NiCrBSi coatings were observed by an optical microscope (Leica, Germany). Then Image J software was used to calculate the coating porosity. The phase structure of the obtained coatings was determined by an X-ray diffractometer (D8 Advance, Germany) with Cu Kα (λ = 1.5405 Å) radiation. The diffraction angle 2θ ranged from 20 to 100° with a scanning rate of 5° min−1. Details of the amorphous peaks from 35 to 55° were scanned with a scanning rate of 1° min−1, and the degree of crystallinity was calculated by the software of Jade 6.0. The microhardness of the coatings was measured by using an HV-1000A hardness tester. Vickers indentation experiments were performed using a load of 100 g and a dwell time of 15 s. Ten indentations on each coating were conducted and an average value was calculated. 2.3. Tribological tests Tribological tests were conducted on a tribometer UMT-2 (Bruker UMT, USA) with ball-on-disk configuration at room temperature under dry condition (without lubrication). Each specimen was
Fig. 1. SEM images of NiCrBSi powder: (a) low magnification and (b) high magnification.
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L. Liu et al. / Surface & Coatings Technology 325 (2017) 548–554 Table 3 Test parameters during friction process. Parameters
Values
Load (N) Reciprocating frequency (Hz) Stroke length (mm) Sliding velocity (mm/s) Sliding time (h) Temperature (°C)
10 2 8 32 4 20
performed for four times to ensure the reliability. Prior to tests, the surface of all specimens was polished with 400, 600, and 1000 grit papers consecutively to ensure the surface roughness Ra less than 0.3 μm. Si3N4 ball with a diameter of 4 mm and hardness of 1700 HV was chosen as the counterpart. More detailed parameters were listed in Table 3. The friction coefficients were recorded automatically to a tester connected
computer. Wear volume and the features of wear tracks were inspected by a three-dimensional optical microscopy (Contour GT-K Bruker, USA). The wear tracks of the coatings were inspected by a field-emission scanning electron microscopy (FE-SEM, S4800II, Japan) equipped with energy dispersive spectroscopy (EDS). 3. Results and discussion 3.1. Coating microstructure The cross-sectional structures of the as-sprayed and heat treated coatings are shown in Fig. 2. APS coatings have a lamellar structure, which contains pores and unmelted particles. With increasing the heat treatment temperature, the black oxides layers between lamellar splats were identified (Fig. 2c and d). To further investigate the effect of temperature on coating oxidation, EDS spot scanning analysis was
Fig. 2. FE-SEM graphs of cross-sectional microstructure of (a) as-sprayed NiCrBSi coating and coatings heat-treated at (b) 300 °C, (c) 500 °C, (d) 700 °C and EDS analysis of (e) point A, (f) point B.
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Fig. 3. Typical binary images of the coatings' cross-section in the inserted optical micrographs: (a) as-sprayed coating, (b) coating treated at 300 °C, (c) coating treated at 500 °C and (d) coating treated at 700 °C.
performed in the thin black layer (point A) and outside of it (point B). The semi-quantitative analysis of the thin black layer revealed the oxygen concentration changed from 0 to 14.3 wt% (Fig. 2e and f). This indicated that high temperature treatment resulted in inter-splat oxidation. Fig. 3 gives the binary images of the cross-sectional surface before and after the heat treatment. The average porosity of the coatings was always about 1.4%, which means the heat treatments at 300–700 °C did not have a significant influence on the porosity. The presence of pores in plasma sprayed coatings can lower the friction between the piston ring and cylinder liner since oil can be conserved in the pores and hence promote the formation of oil film [24].
Fig. 4 shows the XRD patterns of the as-sprayed and heat treated NiCrBSi coatings. It is demonstrated that the phase compositions of the coatings after heat treatment at 300 or 500 °C are similar to those of the as-sprayed coating which mainly consist of γ-(Ni, Fe) solid solution. However, when the temperature was raised to 700 °C, Ni3B and CrB phases were identified. The boride phases are unable to form completely during spraying due to the short retention time in the jet [25,26]. During the heat treatment at 700 °C, atoms diffuse actively, boron atoms diffuse and combine with nickel and chromium atoms to form Ni3B
Fig. 4. X-ray diffraction patterns of the coatings at different heat-treatment temperatures for 1 h. Detailed features of the main peak is given in the insert.
Fig. 5. Microhardness of the as-sprayed coating and coatings heat-treated at 300, 500, 700 °C.
3.2. Phase composition
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3.3. Microhardness As seen from Fig. 5, the heat treatment significantly improved the mechanical properties of NiCrBSi coatings. The average microhardness of the as-sprayed coating was about 728 HV0.1, while it reached 1046 HV0.1 after being heat treated at 700 °C for 1 h. The increment can be attributed to the dispersion strengthening effect provided by the precipitates, such as CrB and Ni3B phases. It is reported that the CrB ceramic phase (nano-hardness 20.31 GPa) is significantly harder than γ(Ni,Fe) solid solution (nano-hardness 5.09 GPa) [22]. It is noted that the nano-hardness value equals to 94.5 times of microhardness [29]. The heat treatment at 300 °C exerted only a slight effect on the coating hardness since the phase change was negligible. When the temperature was increased to 500 °C, the microhardness of the coating was elevated to 890 HV0.1. The heat treatment at 500 °C makes a small quantity of CrB boride phases separate out and act as reinforced phase to enhance the coating hardness [30]. Fig. 6. The friction coefficients of the four coatings versus sliding time.
and CrB phases [27]. The formation of these boride phases reduces the supersaturation of γ-(Ni, Fe) solid solution and alleviates the distortion of the crystalline structure [28]. XRD patterns corroborated the re-crystallization of the coatings due to the heat treatment. The fast cooling rate of the splats led to a low degree of crystallinity. From the insert in Fig. 4, it can be observed that the coatings heat treated at 300 °C presented a broadening peak, which indicated that a significant fraction of amorphous phase was present in the coatings. It was reported that amorphous phase in plasma-sprayed NiCrBSi coatings was metastable and it could transform into Ni4Si, Ni3Si and Ni3B crystalline phases at temperatures from 500 to 700 °C [16]. Li et al. revealed that the critical transition temperature for highvelocity oxygen fuel sprayed NiCrBSi coatings was in the range of 300–500 °C which was lower than that of plasma-sprayed coatings [17]. The crystallinity of the as-sprayed coating and the coatings obtained after treatment at 300 °C and 500 °C were approximately 12%, 16%, 25%, respectively, as calculated from the XRD patterns. After the heat treatment at 700 °C, complete re-crystallization of the amorphous phases arose and they completely transformed into boride, carbides and γ-Ni phases.
Fig. 7. Average wear rates of the four coatings.
3.4. Tribological performance The tribological properties of the coatings were evaluated on a tribometer using a ball-on-disk configuration in linear reciprocating mode. As seen from Fig. 6, the friction coefficients of the coatings varied from 0.63 to 0.70. The friction coefficients increased rapidly during the running-in period. The increment of the friction coefficient during the running-in period is usually accompanied with increased wear rate of NiCrBSi coatings [31]. The heat treatment did not lead to a pronounced effect on the friction coefficients whereas the heat treatment at 700 °C increased the wear rate of the coating, as shown in Fig. 7. The 3D profiles of the wear scars on the coatings are illustrated in Fig. 8. The amorphous coating exhibited a high wear resistance, probably because few grain boundaries were present in the coating and thus the occurrence risk of crack propagation can be low. It is interesting to find that the coating treated at 700 °C exhibited the highest wear rate even it showed the highest microhardness (Figs. 7 and 8). Nevertheless, the heat treatment at 300 °C and 500 °C did not obviously affect the wear rate, in comparison to that of the as-sprayed coating. Fig. 9 shows the FE-SEM graphs of the worn surfaces of the coatings. Severe plastic deformation and some small cracks were noticed from the worn surface of the coating treated at 300 °C. This can give a hint that the coating may show a high toughness. The compacted flake-like particles were observed, such particles are formed owing to debonding of the splats which are often happened in plasma sprayed coatings with poor cohesion strength [32–34]. As a result of repeated stressing on the frictional layer, interlaminar debonding of the splats in the frictional layer can occur due to nucleation and propagation of subsurface cracks [35]. The debonded splats were pulled away from the surface and then compacted back on. In this case, the wear resistance was dominated by the cohesion strength of the coating and the wear mechanism was mainly adhesive wear. The microhardness of the heat-treated NiCrBSi coating at 500 °C was 891 HV0.1 which was only lower than the 700 °C coating, the improvement in coating hardness enhanced resistance to micro-cutting. At the same time, the oxidation between inter-splat layer of the 500 °C coating was lighter than the 700 °C coating seen in Fig. 2. During friction process, the splat debonding was not as severe as the 700 °C coating too. It is worth noting that 500 °C will not lead to a large amount of precipitation and the coating toughness will not reduce much. The worn surface in Fig. 9c reveals that the wear mechanism was mainly adhesive wear and slight abrasive. Comparatively speaking, coatings treated at 500 °C exhibited the best wear resistance. After heat treatment at 700 °C, particles on the worn surface were severely peeled off, as shown in Fig. 9d. High temperature treatment led to precipitation of the hard phases and enhanced the hardness of the coating. On the contrary, the interlaminar oxidation was more severe accompanied with high temperature, which can act as stress
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Fig. 8. Typical 3D images of the wear scars on various coatings: (a) as-sprayed coating, (b) coating treated at 300 °C, (c) coating treated at 500 °C, (d) coating treated at 700 °C and (e) profiles across the worn scars.
raisers and decreases the cohesion strength of the coating [36]. Moreover, the recrystallization occurring during the heat treatment at 700 °C and the precipitation of the hard phases may decrease the toughness of the coating. In this case, abrasive wear was dominant for the wear mechanism. 4. Conclusion NiCrBSi coatings were deposited by atmospheric plasma spraying and further heat treated at 300, 500 and 700 °C. The microstructure, phase compositions, microhardness and tribological properties of the coatings were investigated. Following conclusions can be drawn: (1) All the coatings concerned showed a dense structure with a porosity of about 1.4%. Inter-splat oxidation was identified when the heat temperature was increased. (2) The as-sprayed coating mainly consisted of γ-(Ni, Fe) solid solution. Recrystallization occurred during the heat treatment process and the crystallinity of the coating was enhanced when increasing the heat treatment temperature. Moreover, Ni3B and CrB phases precipitated from the coating during the heat
treatment at 700 °C. (3) The microhardness of the coating heat treated at 300 °C was 725 HV0.1, which was similar to that of as-sprayed coating (728 HV0.1). Owing to the dispersion strengthening effect of the precipitates, the microhardness was improved to 891 and 1046 HV0.1 after the heat treatments at 500 and 700 °C. (4) The heat treatment did not exert a pronounced effect on the friction coefficients of the coatings. Nevertheless, in spite of the enhancement in microhardness, the heat treatment at 700 °C led to a comparatively large wear rate. Possibly reduced inter-splat cohesion and coating toughness should be responsible for the increased wear rate.
Acknowledgements This work was supported by the Jiangsu Natural Science Foundation of China under Grant No. BK20140487 and BK20160472, the Funding of Jiangsu Innovation Program for Graduate Education under Grant No. KYLX16_1387 and Six Talent Peaks Project in Jiangsu Province under Grant No. JXQC-031.
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Fig. 9. FE-SEM micrographs of the worn surfaces of (a) the as-sprayed coating, (b) the coating treated at 300 °C, (c) the coating treated at 500 °C, (d) the coating treated at 700 °C.
References [1] I.C. Grigorescu, C. Di Rauso, R. Drira-Halouani, B. Lavelle, R. Di Giampaolo, J. Lira, Phase characterization in Ni alloy-hard carbide composites for fused coatings, Surf. Coat. Technol. 76-77 (1995) 494–498. [2] F. Otsubo, H. Era, K. Kishitake, Properties of Cr3C2-NiCr cermet coating sprayed by high power plasma and high velocity oxy-fuel processes, J. Therm. Spray Technol. 9 (2000) 499–504. [3] P. Niranatlumpong, H. Koiprasert, Phase transformation of NiCrBSi-WC and NiBSiWC arc sprayed coatings, Surf. Coat. Technol. 206 (2011) 440–445. [4] N. Serres, F. Hlawka, S. Costil, C. Langlade, F. Machi, Microstructure of metallic NiCrBSi coatings manufactured via hybrid plasma spray and in situ laser remelting process, J. Therm. Spray Technol. 20 (2010) 336–343. [5] S. Johansson, C. Frennfelt, A. Killinger, P.H. Nilsson, R. Ohlsson, B.G. Rosén, Frictional evaluation of thermally sprayed coatings applied on the cylinder liner of a heavy duty diesel engine: pilot tribometer analysis and full scale engine test, Wear 273 (2011) 82–92. [6] C. Öner, H. Hazar, M. Nursoy, Surface properties of CrN coated engine cylinders, Mater. Des. 30 (2009) 914–920. [7] G. Barbezat, Advanced thermal spray technology and coating for lightweight engine blocks for the automotive industry, Surf. Coat. Technol. 200 (2005) 1990–1993. [8] G. Barbezat, Application of thermal spraying in the automobile industry, Surf. Coat. Technol. 201 (2006) 2028–2031. [9] K. Bobzin, F. Ernst, J. Zwick, T. Schlaefer, D. Cook, K. Nassenstein, A. Schwenk, F. Schreiber, T. Wenz, G. Flores, M. Hahn, Coating bores of light metal engine blocks with a nanocomposite material using the plasma transferred wire arc thermal spray process, J. Therm. Spray Technol. 17 (2008) 344–351. [10] A. Nakajima, T. Mawatari, M. Yoshida, K. Tani, A. Nakahira, Effects of coating thickness and slip ratio on durability of thermally sprayed WC cermet coating in rolling/sliding contact, Wear 241 (2000) 166–173. [11] P.B. Kadolkar, T.R. Watkins, J.T.M. De Hosson, B.J. Kooi, N.B. Dahotre, State of residual stress in laser-deposited ceramic composite coatings on aluminum alloys, Acta Mater. 55 (2007) 1203–1214. [12] A. Plati, J.C. Tan, I.O. Golosnoy, R. Persoons, K. Van Acker, T.W. Clyne, Residual stress generation during laser cladding of steel with a particulate metal matrix composite, Adv. Eng. Mater. 8 (2006) 619–624. [13] Š. Houdková, E. Smazalová, M. Vostřák, J. Schubert, Properties of NiCrBSi coating, as sprayed and remelted by different technologies, Surf. Coat. Technol. 253 (2014) 14–26. [14] M.S. Yang, X.B. Liu, J.W. Fan, X.M. He, S.H. Shi, G.Y. Fu, M.D. Wang, S.F. Chen, Microstructure and wear behaviors of laser clad NiCr/Cr3C2-WS2 high temperature self-lubricating wear-resistant composite coating, Appl. Surf. Sci. 258 (2012) 3757–3762. [15] S.F. Zhou, X.Y. Zeng, Q.W. Hu, Y.J. Huang, Analysis of crack behavior for Ni-based WC composite coatings by laser cladding and crack-free realization, Appl. Surf. Sci. 255 (2008) 1646–1653. [16] H. Skulev, S. Malinov, P.A.M. Basheer, W. Sha, Modifications of phases, microstructure and hardness of Ni-based alloy plasma coatings due to thermal treatment, Surf. Coat. Technol. 185 (2004) 18–29. [17] C.J. Li, Y.Y. Wang, H. Li, Effect of nano-crystallization of high velocity oxy-fuelsprayed amorphous NiCrBSi alloy on properties of the coatings, J. Vac. Sci. Technol. 22 (2004) 2000–2004.
[18] P.C. Xia, J.J. Yu, X.F. Sun, H.R. Guan, Z.Q. Hu, Influence of heat treatment on the microstructure and mechanical properties of DZ951 alloy, Rare Metals 27 (2008) 216–220. [19] Z. Bergant, J. Grum, Quality improvement of flame sprayed, heat treated, and remelted NiCrBSi coatings, J. Therm. Spray Technol. 18 (2008) 380–391. [20] Z. Bergant, U. Trdan, J. Grum, Effect of high-temperature furnace treatment on the microstructure and corrosion behavior of NiCrBSi flame-sprayed coatings, Corros. Sci. 88 (2014) 372–386. [21] G.J. Li, J. Li, X. Luo, Effects of high temperature treatment on microstructure and mechanical properties of laser-clad NiCrBSi/WC coatings on titanium alloy substrate, Mater. Charact. 98 (2014) 83–92. [22] X.L. Lu, X.B. Liu, P.C. Yu, Y.J. Zhai, S.J. Qiao, M.D. Wang, Y.G. Wang, Y. Chen, Effects of heat treatment on microstructure and mechanical properties of Ni60/h-BN self-lubricating anti-wear composite coatings on 304 stainless steel by laser cladding, Appl. Surf. Sci. 355 (2015) 350–358. [23] ASTM Standard E1920-03, Standard Guide for Metallographic Preparation of Thermal Sprayed Coatings, ASM International, West Conshohocken, PA, 2003 03.01. [24] A. Manzat, A. Killinger, R. Gadow, D. Stuttgart, Supersonic flame sprayed cylinder liner coatings and the benefits of their intrinsic porosityInternational Thermal Spray Conference & Exposition 2011, pp. 489–494 (Hamburg). [25] J.M. Miguel, J.M. Guilemany, S. Vizcaino, Tribological study of NiCrBSi coating obtained by different processes, Tribol. Int. 36 (2003) 181–187. [26] M.P. Planche, H. Liao, B. Normand, C. Coddet, Relationships between NiCrBSi particle characteristics and corresponding coating properties using different thermal spraying processes, Surf. Coat. Technol. 200 (2005) 2465–2473. [27] X.D. Lu, H.M. Wang, High-temperature phase stability and tribological properties of laser clad Mo2Ni3Si/NiSi metal silicide coatings, Acta Mater. 52 (2004) 5419–5426. [28] D.W. Zhang, T.C. Lei, J.G. Zhang, J.H. Ouyang, The effects of heat treatment on microstructure and erosion properties of laser surface-clad Ni-Base alloy, Surf. Coat. Technol. 115 (1999) 176–183. [29] ISO/TC 164, Metallic materials-instrumented indentation test for hardness and material parameters, ISO 14577, 2002-10-01. [30] H.F. Xuan, Q.Y. Wang, S.L. Bai, Z.D. Liu, H.G. Sun, P.C. Yan, A study on microstructure and fame erosion mechanism of a graded Ni-Cr-B-Si coating prepared by laser cladding, Surf. Coat. Technol. 244 (2014) 203–209. [31] P. Niranatlumpong, H. Koiprasert, The effect of Mo content in plasma-sprayed MoNiCrBSi coating on the tribological behavior, Surf. Coat. Technol. 205 (2010) 483–489. [32] L. Hauschmann, J. Siegi, J. Karlik, I.P. Kunes, Chraska plasma sprayed coatings under cyclic contact pressure on a small area, 13th International Thermal Spray Conference (ITSC)ASM International, Orlando, FL, USA 1992, pp. 723–727. [33] R. Nieminen, P. Vuoristo, K. Niemi, T. Mäntylä, G. Barbezat, Rolling contact fatigue failure mechanisms in plasma and HVOF sprayed WC-Co coatings, Wear 212 (1997) 66–67. [34] N.P. Suh, The delamination theory of wear, Wear 25 (1973) 111–124. [35] R. Neupane, Z. Farhat, Wear mechanisms of nitinol under reciprocating sliding contact, Wear 315 (2014) 25–30. [36] V.H. Hidalgo, F.J.B. Varela, A.C. Menéndez, S.P. Martínez, A comparative study of high-temperature erosion wear of plasma-sprayed NiCrBSiFe and WC-NiCrBSiFe coatings under simulated coal-fired boiler conditions, Tribol. Int. 34 (2001) 161–169.
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Effect of heat treatment on structure and property evolutions of atmospheric plasma sprayed NiCrBSi coatings Liming Liu a, Haifeng Xu a, Jinkun Xiao a, Xinlong Wei a, Ga Zhang b, Chao Zhang a,⁎ a b
College of Mechanical Engineering, Yangzhou University, Yangzhou 225127, China State Key Laboratory of Solid Lubrication, Lanzhou Institute of Chemical Physics, Chinese Academy of Sciences, Lanzhou 730000, China
a r t i c l e
i n f o
Article history: Received 8 May 2017 Revised 30 June 2017 Accepted in revised form 3 July 2017 Available online 04 July 2017 Keywords: Plasma spray NiCrBSi coating Heat treatment Microstructure Wear resistance
a b s t r a c t To investigate the evolutions of structures and properties of NiCrBSi coatings on cylinder liner of engines during its service, atmospheric plasma sprayed (APS) NiCrBSi coatings were heat treated at 300, 500, or 700 °C in this work. The effect of heat treatment on microstructure, phase composition, microhardness and tribological performance has been investigated. It was identified that as-sprayed coatings mainly consisted of γ-(Ni, Fe) phase while CrB and Ni3B phases precipitated from the coatings during the heat treatments at 500 and 700 °C. In addition, inter-splat oxidation of the coating during the heat treatment occurred. Moreover, the crystallinity of the coating was significantly enhanced with increasing the heat treatment temperature. The heat treatment improved obviously the microhardness whereas it did not exert a pronounced effect on the friction coefficients of the coatings. In spite of the enhanced microhardness, the heat treatment at 700 °C increased the wear rate comparatively. It was revealed that inter-splat debonding of the coating surface layer involved in the friction dominated the wear resistance of the coating. Inter-splat oxidation and reduction of coating toughness due to heat treatment can account for the increased wear rate. © 2017 Elsevier B.V. All rights reserved.
1. Introduction Nickel-based alloys are widely applied for corrosion and wear resistant application. NiCrBSi is a self-fluxing alloy, and the presence of B and Si not only enhances the self-fluxing property of the metal which is favorable for coating deposition but also forms hard phase with Ni, such as Ni3B [1,2]. In addition, chromium can further improve its corrosion and wear resistance through the precipitation of hard particles [3]. Thermally sprayed NiCrBSi coatings are currently considered to be a potential substitute of conventional electroplating hard chromium layer applied for cylinder liner of diesel engine [4]. The most important set of components in modern engines is cylinder unit, which accounts for about half of the total frictional loss [5,6]. A typical material used for cylinder liner of the diesel engine is casting iron. However, for long-term applications, utilization of cast iron showed obvious disadvantages, such as high power consumption, low wear resistance, easy to corrosion, low fuel efficiency and incomplete combustion, etc. [7]. Plasma spraying has been identified in recent years as a promising solution to deposit protection coatings on cylinder liners for enhancing their lifetime [8,9]. However, coating delamination may occur due to
⁎ Corresponding author. E-mail addresses: [email protected], [email protected] (C. Zhang).
http://dx.doi.org/10.1016/j.surfcoat.2017.07.011 0257-8972/© 2017 Elsevier B.V. All rights reserved.
residual stress in the coating and unmatched elastic modulus, distinct thermal expansion coefficients between the coating and substrate [10–12]. Moreover, cracks, pores, oxides and unmelted particles are usually inevitable in plasma-sprayed coatings, which can lower the tribological performance [13–15]. On the other hand, plasma spraying is a rapid melting and solidification process, and thus numerous amorphous phases readily form in as-sprayed coatings. Previous works have reported that nickel-based thermally sprayed coatings containing amorphous structures exhibit high hardness and wear-corrosion resistance [16,17]. Nevertheless, the amorphous structures are metastable, and therefore recrystallization may occur when the coatings are exposed to high-temperature conditions during its service. As known that the service temperature of water cool cylinder liner is in a range of 300–500 °C. Hence, the precipitated grains in the deposited coating can evolve during its service, which can exert an influence on the hardness and wear resistance. That is, the structure and performance of the coating can vary as a function of service time and temperature. Post heat treatment is usually helpful for getting a dense coating with high cohesion and adhesion strengths [18]. Bergant et al. [19,20] investigated the effects of heat treatment and remelting on the quality of flame sprayed NiCrBSi coatings, and the authors demonstrated that the adhesion between coating and substrate after a 930 °C heat treatment was obviously enhanced. Moreover, denser NiCrBSi coatings with a homogeneous microstructure, low porosity and low residual stress were achieved by 5-minute remelting treatment. Li et al. [21]
L. Liu et al. / Surface & Coatings Technology 325 (2017) 548–554 Table 1 Chemical composition of NiCrBSi powders.
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Table 2 Selected plasma spraying parameters.
Element
Ni
Cr
B
Si
Fe
C
Parameters
Values
wt%
Bal.
17.53
3.27
4.01
4.43
0.82
Primary gas, Ar (L/min) Secondary gas, H2 (L/min) Plasma current (A) Plasma voltage (V) Powder feed rate (g/min) Spraying distance (mm) Gun translation velocity (mm/s)
55 7.5 516 64 60 140 200
studied the influence of heat treatment on microstructure and mechanical properties of NiCrBSi/WC coatings. Their results showed that the heat treatment at 900 °C for 1 h not only improved the hardness and fracture toughness but also reduced the wear rate, frictions coefficient and cracking susceptibility of the coatings. Lu et al. [22] analyzed the effects of heat treatment at 600 °C on microstructure and mechanical properties of laser cladded Ni60/h-BN self-lubricating composite coatings, and they disclosed that the residual stress in the coating was relieved after the heat treatment. In addition, the microhardness and elastic modulus of the coatings were enhanced in comparison to those of the as-cladded coatings. The heat treatment at 600 °C for 1 h showed the best wear resistance. Nevertheless, most of the previously works were limited to high temperature heat treatment and even remelting of NiCrBSi based coatings. The results are not enough to elucidate the evolution of coating microstructure and properties under real working conditions of the cylinder liner. The aim of this work was to study the effect of service temperature on microstructure evolution and tribological properties of atmospheric plasma-sprayed NiCrBSi coatings. Taking into account the service temperature of atmospheric plasma-sprayed NiCrBSi coatings in cylinder liners, the heat treatments at 300, 500, and 700 °C for 1 h were adopted in this work. The microstructure, phase composition and microhardness of as-sprayed and heat treated coatings were characterized. The tribological properties of the as-sprayed and heat treated coatings were examined. The wear mechanisms of the coatings were investigated.
2. Experimental procedure 2.1. Sample preparation Commercially available gas atomized NiCrBSi powders with a particle size ranging from 40 to 60 μm were chosen as feedstock materials. The composition of the powders was listed in Table 1. As seen from Fig. 1, the powders present a spherical shape which is beneficial to get good fluidity during plasma spraying process. 304 stainless steel plates (size: 60 mm × 40 mm × 3 mm) were used as substrates. Prior to spraying, the substrates were grit blasted by 24 mesh brown corundum to activate the surface. The coating deposition was carried out using an F4MB-XL plasma gun (Oerlikon Metco, Switzerland). A six-axis robot manipulator (ABB, Sweden) was used to get a uniform movement of the plasma gun. The
optimized spraying parameters were given in Table 2. The feedstock material was injected vertically into the plasma torch by Ar carrier gas. To reduce the substrate temperature, compressed air was placed at the back of the substrates at a pressure of 0.3 MPa as cooling gas. The as-sprayed coatings had a thickness of approximately 350 μm. After deposition, the coatings were cut into small specimens by a cutting machine for heat treatment and further analysis. Coated specimens were buried in a crucible filled with alumina powders to ensure the uniform heating. The heat treatments at 300, 500, or 700 °C were carried out in a muffle furnace with a heating rate of 10 °C/min. After reaching the set temperature and keep for 1 h, the specimens were removed from the furnace and cooled in air subsequently. 2.2. Coating characterization Ten specimens for each condition were prepared to analyze the microstructure and porosity of the coatings [23]. The cross-sectional morphologies of the as-sprayed and heat treated NiCrBSi coatings were observed by an optical microscope (Leica, Germany). Then Image J software was used to calculate the coating porosity. The phase structure of the obtained coatings was determined by an X-ray diffractometer (D8 Advance, Germany) with Cu Kα (λ = 1.5405 Å) radiation. The diffraction angle 2θ ranged from 20 to 100° with a scanning rate of 5° min−1. Details of the amorphous peaks from 35 to 55° were scanned with a scanning rate of 1° min−1, and the degree of crystallinity was calculated by the software of Jade 6.0. The microhardness of the coatings was measured by using an HV-1000A hardness tester. Vickers indentation experiments were performed using a load of 100 g and a dwell time of 15 s. Ten indentations on each coating were conducted and an average value was calculated. 2.3. Tribological tests Tribological tests were conducted on a tribometer UMT-2 (Bruker UMT, USA) with ball-on-disk configuration at room temperature under dry condition (without lubrication). Each specimen was
Fig. 1. SEM images of NiCrBSi powder: (a) low magnification and (b) high magnification.
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L. Liu et al. / Surface & Coatings Technology 325 (2017) 548–554 Table 3 Test parameters during friction process. Parameters
Values
Load (N) Reciprocating frequency (Hz) Stroke length (mm) Sliding velocity (mm/s) Sliding time (h) Temperature (°C)
10 2 8 32 4 20
performed for four times to ensure the reliability. Prior to tests, the surface of all specimens was polished with 400, 600, and 1000 grit papers consecutively to ensure the surface roughness Ra less than 0.3 μm. Si3N4 ball with a diameter of 4 mm and hardness of 1700 HV was chosen as the counterpart. More detailed parameters were listed in Table 3. The friction coefficients were recorded automatically to a tester connected
computer. Wear volume and the features of wear tracks were inspected by a three-dimensional optical microscopy (Contour GT-K Bruker, USA). The wear tracks of the coatings were inspected by a field-emission scanning electron microscopy (FE-SEM, S4800II, Japan) equipped with energy dispersive spectroscopy (EDS). 3. Results and discussion 3.1. Coating microstructure The cross-sectional structures of the as-sprayed and heat treated coatings are shown in Fig. 2. APS coatings have a lamellar structure, which contains pores and unmelted particles. With increasing the heat treatment temperature, the black oxides layers between lamellar splats were identified (Fig. 2c and d). To further investigate the effect of temperature on coating oxidation, EDS spot scanning analysis was
Fig. 2. FE-SEM graphs of cross-sectional microstructure of (a) as-sprayed NiCrBSi coating and coatings heat-treated at (b) 300 °C, (c) 500 °C, (d) 700 °C and EDS analysis of (e) point A, (f) point B.
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Fig. 3. Typical binary images of the coatings' cross-section in the inserted optical micrographs: (a) as-sprayed coating, (b) coating treated at 300 °C, (c) coating treated at 500 °C and (d) coating treated at 700 °C.
performed in the thin black layer (point A) and outside of it (point B). The semi-quantitative analysis of the thin black layer revealed the oxygen concentration changed from 0 to 14.3 wt% (Fig. 2e and f). This indicated that high temperature treatment resulted in inter-splat oxidation. Fig. 3 gives the binary images of the cross-sectional surface before and after the heat treatment. The average porosity of the coatings was always about 1.4%, which means the heat treatments at 300–700 °C did not have a significant influence on the porosity. The presence of pores in plasma sprayed coatings can lower the friction between the piston ring and cylinder liner since oil can be conserved in the pores and hence promote the formation of oil film [24].
Fig. 4 shows the XRD patterns of the as-sprayed and heat treated NiCrBSi coatings. It is demonstrated that the phase compositions of the coatings after heat treatment at 300 or 500 °C are similar to those of the as-sprayed coating which mainly consist of γ-(Ni, Fe) solid solution. However, when the temperature was raised to 700 °C, Ni3B and CrB phases were identified. The boride phases are unable to form completely during spraying due to the short retention time in the jet [25,26]. During the heat treatment at 700 °C, atoms diffuse actively, boron atoms diffuse and combine with nickel and chromium atoms to form Ni3B
Fig. 4. X-ray diffraction patterns of the coatings at different heat-treatment temperatures for 1 h. Detailed features of the main peak is given in the insert.
Fig. 5. Microhardness of the as-sprayed coating and coatings heat-treated at 300, 500, 700 °C.
3.2. Phase composition
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3.3. Microhardness As seen from Fig. 5, the heat treatment significantly improved the mechanical properties of NiCrBSi coatings. The average microhardness of the as-sprayed coating was about 728 HV0.1, while it reached 1046 HV0.1 after being heat treated at 700 °C for 1 h. The increment can be attributed to the dispersion strengthening effect provided by the precipitates, such as CrB and Ni3B phases. It is reported that the CrB ceramic phase (nano-hardness 20.31 GPa) is significantly harder than γ(Ni,Fe) solid solution (nano-hardness 5.09 GPa) [22]. It is noted that the nano-hardness value equals to 94.5 times of microhardness [29]. The heat treatment at 300 °C exerted only a slight effect on the coating hardness since the phase change was negligible. When the temperature was increased to 500 °C, the microhardness of the coating was elevated to 890 HV0.1. The heat treatment at 500 °C makes a small quantity of CrB boride phases separate out and act as reinforced phase to enhance the coating hardness [30]. Fig. 6. The friction coefficients of the four coatings versus sliding time.
and CrB phases [27]. The formation of these boride phases reduces the supersaturation of γ-(Ni, Fe) solid solution and alleviates the distortion of the crystalline structure [28]. XRD patterns corroborated the re-crystallization of the coatings due to the heat treatment. The fast cooling rate of the splats led to a low degree of crystallinity. From the insert in Fig. 4, it can be observed that the coatings heat treated at 300 °C presented a broadening peak, which indicated that a significant fraction of amorphous phase was present in the coatings. It was reported that amorphous phase in plasma-sprayed NiCrBSi coatings was metastable and it could transform into Ni4Si, Ni3Si and Ni3B crystalline phases at temperatures from 500 to 700 °C [16]. Li et al. revealed that the critical transition temperature for highvelocity oxygen fuel sprayed NiCrBSi coatings was in the range of 300–500 °C which was lower than that of plasma-sprayed coatings [17]. The crystallinity of the as-sprayed coating and the coatings obtained after treatment at 300 °C and 500 °C were approximately 12%, 16%, 25%, respectively, as calculated from the XRD patterns. After the heat treatment at 700 °C, complete re-crystallization of the amorphous phases arose and they completely transformed into boride, carbides and γ-Ni phases.
Fig. 7. Average wear rates of the four coatings.
3.4. Tribological performance The tribological properties of the coatings were evaluated on a tribometer using a ball-on-disk configuration in linear reciprocating mode. As seen from Fig. 6, the friction coefficients of the coatings varied from 0.63 to 0.70. The friction coefficients increased rapidly during the running-in period. The increment of the friction coefficient during the running-in period is usually accompanied with increased wear rate of NiCrBSi coatings [31]. The heat treatment did not lead to a pronounced effect on the friction coefficients whereas the heat treatment at 700 °C increased the wear rate of the coating, as shown in Fig. 7. The 3D profiles of the wear scars on the coatings are illustrated in Fig. 8. The amorphous coating exhibited a high wear resistance, probably because few grain boundaries were present in the coating and thus the occurrence risk of crack propagation can be low. It is interesting to find that the coating treated at 700 °C exhibited the highest wear rate even it showed the highest microhardness (Figs. 7 and 8). Nevertheless, the heat treatment at 300 °C and 500 °C did not obviously affect the wear rate, in comparison to that of the as-sprayed coating. Fig. 9 shows the FE-SEM graphs of the worn surfaces of the coatings. Severe plastic deformation and some small cracks were noticed from the worn surface of the coating treated at 300 °C. This can give a hint that the coating may show a high toughness. The compacted flake-like particles were observed, such particles are formed owing to debonding of the splats which are often happened in plasma sprayed coatings with poor cohesion strength [32–34]. As a result of repeated stressing on the frictional layer, interlaminar debonding of the splats in the frictional layer can occur due to nucleation and propagation of subsurface cracks [35]. The debonded splats were pulled away from the surface and then compacted back on. In this case, the wear resistance was dominated by the cohesion strength of the coating and the wear mechanism was mainly adhesive wear. The microhardness of the heat-treated NiCrBSi coating at 500 °C was 891 HV0.1 which was only lower than the 700 °C coating, the improvement in coating hardness enhanced resistance to micro-cutting. At the same time, the oxidation between inter-splat layer of the 500 °C coating was lighter than the 700 °C coating seen in Fig. 2. During friction process, the splat debonding was not as severe as the 700 °C coating too. It is worth noting that 500 °C will not lead to a large amount of precipitation and the coating toughness will not reduce much. The worn surface in Fig. 9c reveals that the wear mechanism was mainly adhesive wear and slight abrasive. Comparatively speaking, coatings treated at 500 °C exhibited the best wear resistance. After heat treatment at 700 °C, particles on the worn surface were severely peeled off, as shown in Fig. 9d. High temperature treatment led to precipitation of the hard phases and enhanced the hardness of the coating. On the contrary, the interlaminar oxidation was more severe accompanied with high temperature, which can act as stress
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Fig. 8. Typical 3D images of the wear scars on various coatings: (a) as-sprayed coating, (b) coating treated at 300 °C, (c) coating treated at 500 °C, (d) coating treated at 700 °C and (e) profiles across the worn scars.
raisers and decreases the cohesion strength of the coating [36]. Moreover, the recrystallization occurring during the heat treatment at 700 °C and the precipitation of the hard phases may decrease the toughness of the coating. In this case, abrasive wear was dominant for the wear mechanism. 4. Conclusion NiCrBSi coatings were deposited by atmospheric plasma spraying and further heat treated at 300, 500 and 700 °C. The microstructure, phase compositions, microhardness and tribological properties of the coatings were investigated. Following conclusions can be drawn: (1) All the coatings concerned showed a dense structure with a porosity of about 1.4%. Inter-splat oxidation was identified when the heat temperature was increased. (2) The as-sprayed coating mainly consisted of γ-(Ni, Fe) solid solution. Recrystallization occurred during the heat treatment process and the crystallinity of the coating was enhanced when increasing the heat treatment temperature. Moreover, Ni3B and CrB phases precipitated from the coating during the heat
treatment at 700 °C. (3) The microhardness of the coating heat treated at 300 °C was 725 HV0.1, which was similar to that of as-sprayed coating (728 HV0.1). Owing to the dispersion strengthening effect of the precipitates, the microhardness was improved to 891 and 1046 HV0.1 after the heat treatments at 500 and 700 °C. (4) The heat treatment did not exert a pronounced effect on the friction coefficients of the coatings. Nevertheless, in spite of the enhancement in microhardness, the heat treatment at 700 °C led to a comparatively large wear rate. Possibly reduced inter-splat cohesion and coating toughness should be responsible for the increased wear rate.
Acknowledgements This work was supported by the Jiangsu Natural Science Foundation of China under Grant No. BK20140487 and BK20160472, the Funding of Jiangsu Innovation Program for Graduate Education under Grant No. KYLX16_1387 and Six Talent Peaks Project in Jiangsu Province under Grant No. JXQC-031.
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Fig. 9. FE-SEM micrographs of the worn surfaces of (a) the as-sprayed coating, (b) the coating treated at 300 °C, (c) the coating treated at 500 °C, (d) the coating treated at 700 °C.
References [1] I.C. Grigorescu, C. Di Rauso, R. Drira-Halouani, B. Lavelle, R. Di Giampaolo, J. Lira, Phase characterization in Ni alloy-hard carbide composites for fused coatings, Surf. Coat. Technol. 76-77 (1995) 494–498. [2] F. Otsubo, H. Era, K. Kishitake, Properties of Cr3C2-NiCr cermet coating sprayed by high power plasma and high velocity oxy-fuel processes, J. Therm. Spray Technol. 9 (2000) 499–504. [3] P. Niranatlumpong, H. Koiprasert, Phase transformation of NiCrBSi-WC and NiBSiWC arc sprayed coatings, Surf. Coat. Technol. 206 (2011) 440–445. [4] N. Serres, F. Hlawka, S. Costil, C. Langlade, F. Machi, Microstructure of metallic NiCrBSi coatings manufactured via hybrid plasma spray and in situ laser remelting process, J. Therm. Spray Technol. 20 (2010) 336–343. [5] S. Johansson, C. Frennfelt, A. Killinger, P.H. Nilsson, R. Ohlsson, B.G. Rosén, Frictional evaluation of thermally sprayed coatings applied on the cylinder liner of a heavy duty diesel engine: pilot tribometer analysis and full scale engine test, Wear 273 (2011) 82–92. [6] C. Öner, H. Hazar, M. Nursoy, Surface properties of CrN coated engine cylinders, Mater. Des. 30 (2009) 914–920. [7] G. Barbezat, Advanced thermal spray technology and coating for lightweight engine blocks for the automotive industry, Surf. Coat. Technol. 200 (2005) 1990–1993. [8] G. Barbezat, Application of thermal spraying in the automobile industry, Surf. Coat. Technol. 201 (2006) 2028–2031. [9] K. Bobzin, F. Ernst, J. Zwick, T. Schlaefer, D. Cook, K. Nassenstein, A. Schwenk, F. Schreiber, T. Wenz, G. Flores, M. Hahn, Coating bores of light metal engine blocks with a nanocomposite material using the plasma transferred wire arc thermal spray process, J. Therm. Spray Technol. 17 (2008) 344–351. [10] A. Nakajima, T. Mawatari, M. Yoshida, K. Tani, A. Nakahira, Effects of coating thickness and slip ratio on durability of thermally sprayed WC cermet coating in rolling/sliding contact, Wear 241 (2000) 166–173. [11] P.B. Kadolkar, T.R. Watkins, J.T.M. De Hosson, B.J. Kooi, N.B. Dahotre, State of residual stress in laser-deposited ceramic composite coatings on aluminum alloys, Acta Mater. 55 (2007) 1203–1214. [12] A. Plati, J.C. Tan, I.O. Golosnoy, R. Persoons, K. Van Acker, T.W. Clyne, Residual stress generation during laser cladding of steel with a particulate metal matrix composite, Adv. Eng. Mater. 8 (2006) 619–624. [13] Š. Houdková, E. Smazalová, M. Vostřák, J. Schubert, Properties of NiCrBSi coating, as sprayed and remelted by different technologies, Surf. Coat. Technol. 253 (2014) 14–26. [14] M.S. Yang, X.B. Liu, J.W. Fan, X.M. He, S.H. Shi, G.Y. Fu, M.D. Wang, S.F. Chen, Microstructure and wear behaviors of laser clad NiCr/Cr3C2-WS2 high temperature self-lubricating wear-resistant composite coating, Appl. Surf. Sci. 258 (2012) 3757–3762. [15] S.F. Zhou, X.Y. Zeng, Q.W. Hu, Y.J. Huang, Analysis of crack behavior for Ni-based WC composite coatings by laser cladding and crack-free realization, Appl. Surf. Sci. 255 (2008) 1646–1653. [16] H. Skulev, S. Malinov, P.A.M. Basheer, W. Sha, Modifications of phases, microstructure and hardness of Ni-based alloy plasma coatings due to thermal treatment, Surf. Coat. Technol. 185 (2004) 18–29. [17] C.J. Li, Y.Y. Wang, H. Li, Effect of nano-crystallization of high velocity oxy-fuelsprayed amorphous NiCrBSi alloy on properties of the coatings, J. Vac. Sci. Technol. 22 (2004) 2000–2004.
[18] P.C. Xia, J.J. Yu, X.F. Sun, H.R. Guan, Z.Q. Hu, Influence of heat treatment on the microstructure and mechanical properties of DZ951 alloy, Rare Metals 27 (2008) 216–220. [19] Z. Bergant, J. Grum, Quality improvement of flame sprayed, heat treated, and remelted NiCrBSi coatings, J. Therm. Spray Technol. 18 (2008) 380–391. [20] Z. Bergant, U. Trdan, J. Grum, Effect of high-temperature furnace treatment on the microstructure and corrosion behavior of NiCrBSi flame-sprayed coatings, Corros. Sci. 88 (2014) 372–386. [21] G.J. Li, J. Li, X. Luo, Effects of high temperature treatment on microstructure and mechanical properties of laser-clad NiCrBSi/WC coatings on titanium alloy substrate, Mater. Charact. 98 (2014) 83–92. [22] X.L. Lu, X.B. Liu, P.C. Yu, Y.J. Zhai, S.J. Qiao, M.D. Wang, Y.G. Wang, Y. Chen, Effects of heat treatment on microstructure and mechanical properties of Ni60/h-BN self-lubricating anti-wear composite coatings on 304 stainless steel by laser cladding, Appl. Surf. Sci. 355 (2015) 350–358. [23] ASTM Standard E1920-03, Standard Guide for Metallographic Preparation of Thermal Sprayed Coatings, ASM International, West Conshohocken, PA, 2003 03.01. [24] A. Manzat, A. Killinger, R. Gadow, D. Stuttgart, Supersonic flame sprayed cylinder liner coatings and the benefits of their intrinsic porosityInternational Thermal Spray Conference & Exposition 2011, pp. 489–494 (Hamburg). [25] J.M. Miguel, J.M. Guilemany, S. Vizcaino, Tribological study of NiCrBSi coating obtained by different processes, Tribol. Int. 36 (2003) 181–187. [26] M.P. Planche, H. Liao, B. Normand, C. Coddet, Relationships between NiCrBSi particle characteristics and corresponding coating properties using different thermal spraying processes, Surf. Coat. Technol. 200 (2005) 2465–2473. [27] X.D. Lu, H.M. Wang, High-temperature phase stability and tribological properties of laser clad Mo2Ni3Si/NiSi metal silicide coatings, Acta Mater. 52 (2004) 5419–5426. [28] D.W. Zhang, T.C. Lei, J.G. Zhang, J.H. Ouyang, The effects of heat treatment on microstructure and erosion properties of laser surface-clad Ni-Base alloy, Surf. Coat. Technol. 115 (1999) 176–183. [29] ISO/TC 164, Metallic materials-instrumented indentation test for hardness and material parameters, ISO 14577, 2002-10-01. [30] H.F. Xuan, Q.Y. Wang, S.L. Bai, Z.D. Liu, H.G. Sun, P.C. Yan, A study on microstructure and fame erosion mechanism of a graded Ni-Cr-B-Si coating prepared by laser cladding, Surf. Coat. Technol. 244 (2014) 203–209. [31] P. Niranatlumpong, H. Koiprasert, The effect of Mo content in plasma-sprayed MoNiCrBSi coating on the tribological behavior, Surf. Coat. Technol. 205 (2010) 483–489. [32] L. Hauschmann, J. Siegi, J. Karlik, I.P. Kunes, Chraska plasma sprayed coatings under cyclic contact pressure on a small area, 13th International Thermal Spray Conference (ITSC)ASM International, Orlando, FL, USA 1992, pp. 723–727. [33] R. Nieminen, P. Vuoristo, K. Niemi, T. Mäntylä, G. Barbezat, Rolling contact fatigue failure mechanisms in plasma and HVOF sprayed WC-Co coatings, Wear 212 (1997) 66–67. [34] N.P. Suh, The delamination theory of wear, Wear 25 (1973) 111–124. [35] R. Neupane, Z. Farhat, Wear mechanisms of nitinol under reciprocating sliding contact, Wear 315 (2014) 25–30. [36] V.H. Hidalgo, F.J.B. Varela, A.C. Menéndez, S.P. Martínez, A comparative study of high-temperature erosion wear of plasma-sprayed NiCrBSiFe and WC-NiCrBSiFe coatings under simulated coal-fired boiler conditions, Tribol. Int. 34 (2001) 161–169.