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Ni-based composite coatings by laser cladding for self-lubricating applications
Optics and Laser Technology 126 (2020) 106077
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Fabrication and tribological behaviors of Ti3SiC2/Ti5Si3/TiC/Ni-based composite coatings by laser cladding for self-lubricating applications
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Hua Yan , Kaiwei Liu, Peilei Zhang, Jian Zhao, Yang Qin, Qinghua Lu, Zhishui Yu School of Materials Engineering, Shanghai University of Engineering Science, Shanghai 201620, PR China Shanghai Collaborated Innovation Center of Laser Advanced Manufacturing Technology, Shanghai 201620, PR China
H I GH L IG H T S
(Ti SiC ) and Ti Si silicide composite coatings were successfully prepared by in-situ synthesis laser cladding. • MAX self-lubricating properties of the coatings are attributed to Ti SiC , Ti Si and TiC. • Excellent • Laser-clad Ti SiC /Ti Si /TiC/Ni-based composite coatings exhibit small amount of adhesive wear, plastic deformation. 3
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Keywords: Ti-Si-C Laser cladding In-situ reaction Ti3SiC2 Self-lubricating
In the work the in-situ synthesis of Ti3SiC2 (MAX) phase and silicide reinforced Ni-based composite self-lubricating coatings from Ti-Si-C system and NiCrBSi powders were carried and initiated by laser cladding with use of 5 kW fiber laser beam with 3 mm spot. The microstructures of the laser-clad in situ synthetic self-lubricating coatings were analyzed by a scanning electron microscope (SEM) equipped with an X-ray energy dispersive spectrometer (EDS). An X-ray diffraction (XRD) spectrometer and an electron back-scattered diffraction (EBSD) were used for determination of the reaction products in the composite coatings. The friction and abrasion behavior of the coatings were evaluated at room temperature by a dry sliding friction tester. The results indicate that in-situ chemical reactions took place between elements Ti, Si and C in the laser molten pool, and the reaction products included Ti3SiC2, Ti5Si3, and TiC ceramics as well as TiNix compound. Finally, three laser-clad Ti3SiC2/Ti5Si3/TiC/Ni-based composite coatings with the total thickness about 1 mm were fabricated on Ti6Al4V alloy. The average microhardness of the three coatings was 703.2 HV0.2, 751.9 HV0.2 and 850.6 HV0.2 respectively, which has been significantly improved, compared with the hardness of Ti6Al4V substrate (about 360 HV0.2). The average friction coefficient of the Ti3SiC2/Ti5Si3/TiC/Ni-based composite coating (50 wt% Ni25/50 wt% Ti-Si-C) reduced to 0.33 at room temperature, and it exhibited the wear rate of 13.5 × 10−5 mm3 N−1 m−1. The laser cladding Ti3SiC2/Ti5Si3/TiC/Ni-based composite coatings characterized by small amount of adhesive wear, plastic deformation and relatively smooth wear surface could be observed.
1. Introduction Titanium alloys are very important material and widely used in aerospace, biomedical and automatic products due to their excellent inherent properties such as superior strength-to-weight ratio, good heat resistance and excellent corrosion resistance [1,2]. Nevertheless, the application of titanium alloys in friction drive mechanism, especially as a wear resistant rotating part has been severe limitation in the application of key coupling piece because of its low hardness, high friction coefficient, poor wear resistance and low oxidation resistance at high temperature [3,4]. Generally speaking, the failure of working parts
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starts forms their surfaces, where the part is more susceptible to failure under corrosion and wears conditions [5]. Therefore, there is an active demand in industrial production to improve the surface wear behavior including poor wear resistance and low hardness. For the past few years, laser surface cladding (LSC) has favorable characteristics, such as well metallurgical bond between substrate and coating, low dilution rate, high cooling rate, high dense microstructure. Due to the satisfactory characteristics, LSC has been widely used to manufacture composite coatings owning high hardness and outstanding tribological properties [6,7]. Significant processes of LSC have been made on improving abrasion resistance of Ti6Al4V to prepare metal matrix composites
Corresponding author at: School of Materials Engineering, Shanghai University of Engineering Science, Shanghai 201620, PR China. E-mail addresses: [email protected], [email protected] (H. Yan).
https://doi.org/10.1016/j.optlastec.2020.106077 Received 21 October 2019; Received in revised form 3 January 2020; Accepted 13 January 2020 0030-3992/ © 2020 Elsevier Ltd. All rights reserved.
Optics and Laser Technology 126 (2020) 106077
H. Yan, et al.
(MMC) reinforced by the ceramic particles and solid lubricants [8]. The Ti3SiC2 is one of the best-characterized Mn+1AXn phases (where M is an early transition metal, A is a group 13–16 element, X is either C or N). It has excellent high temperature high thermal shock resistance and strength and was first synthesized by W. Jeitschko and H. Nowotny [9–11]. Ti3SiC2 is famous as a new type ceramic has a hexagonal crystalline lattice and the crystalline structure shows a typical laminate characteristic, which has the properties of metal materials and ceramic, such as high thermal stability, high melting point, good self-lubricity and excellent electrical and thermal conductivities [12,13]. Hai [14] et al. investigated the friction and wear of self-mated Ti3SiC2 under unlubricated condition and lubrication of PbO powders at different temperatures. They found that the microstructure and chemical composition have a strong effect on the friction and wear of self-mated Ti3SiC2 under lubrication of PbO powders. Aiming at improving the wear resistance of 35CrMo steel, Li [15] et al also fabricated Ti3SiC2/ Co-based composites coatings on 35CrMo steel by LSC. Experimental results showed that Ti3SiC2 partially dissolved to form TiC. The microhardness of the coatings was significantly enhanced, which was at least 2.3 times that of substrate. Recently, design and preparation of Ti6Al4V/Ti-Si-C system functional gradient material (FGM) as well as the related principle were studied by Li et al [16]. Their research results indicate that in-situ chemical reactions took place between elements Ti, Si and C in the deposited layers, and the reaction products included TiC and Ti3SiC2 ceramics as well as Ti5Si3 compound. In the literature there are negligible information concerning LSC synthesis of Ti3SiC2 phase on Ti6Al4V surface to improve its tribological properties. It is worth to pay attention to that the high energy density and concentricity of laser beam will lead Ti3SiC2 or other solid lubricant and influence the practicality of laser cladding self-lubricating composite coatings in industrial production [17]. To the best knowledge of authors, there is little information available in the literature about the synthesis of Ti3SiC2 coating on Ti6Al4V substrate using LSC technique. In this work, the objective is focusing on the in-situ reaction synthesis to fabricate the self-lubricating composite coatings that contains solid-lubricant phase Ti3SiC2 and silicide reinforcement, as well as exploring the idea that Ti3SiC2 and silicide reinforced particles contribute to improving the microstructural evolution of the coatings. In addition, the tribological behavior and wear mechanisms of LSC self-lubricating coatings from NiCrBSi/Ti-Si-C system (Ti powder, Si powder and nano graphite) were also discussed.
Table 2 Compositions of Ni25 powders (wt. %).
Table 1 Powder mixtures used for LSC.
N1 N2 N3
Components (wt. %) Ti
Si
Nano-graphite
30 50 70
49.98 28.56 21.42
11.69 6.68 5.01
8.33 4.76 3.57
C
Si
Fe
Ni
Content
1.75
0.06
6.91
0.26
Bal.
superior properties, such as pseudo-elasticity toughness and ductility as in our previous research papers [18]. The Ti-Si-C system powders molar ratio of Ti powder, Si powder and nano-graphite was 3:1.2:2. The mass ratios of Ni25 and Ti-Si-C were 3:7, 5:5 and 7:3, respectively. The mixed composite powders were preliminarily placed on the Ti6Al4V alloy by an organic binder with a thickness of 1.5 mm as our previous studies [18–20], and then oven dried before LSC. Powder mixtures were designated as N1, N2 and N3 coatings as in Table 1. The LSC experiment was carried out using an IPG-YLS-5000 fiber laser system with an inert gas protection device which is shown in Fig. 1. The optimized parameters utilized in the experiments are as follows: laser power 1.8 kW, scanning speed 15 mm/s, and spot diameter 3 mm. Argon was selected as the protective gas with a flow rate 10 L/min. The protective gas was switched on three seconds before laser cladding procedure until three seconds after the procedure finished. Then the single track and overlapped coatings with an overlap rate of 40% were cooled in air. After laser cladding, the test samples were cut by wire cut electric discharge machine for microstructure observation and friction-wear testing. A detailed characterization of the composite coatings in terms of microstructure, phases, microhardness, wear resistance and coefficient friction have been undertaken and the effect of precursor powder composition were studied. The cross-sections of the samples were prepared for microstructure analyses. X-ray diffraction (XRD) test (Cu Kα, 1.54 Å wavelength radiations) was employed to identify the phases of the coatings by an X'Pert PRO X-ray Generator machine. Scanning electron-microscopy (Hitachi/S-3400) with energy dispersive spectroscopy (EDS) were used to study the microstructure and to characterize the elemental distribution in a semiquantitative manner. Microhardness at the cross-section of the coatings was measured with Vicker microhardness testing machine (HXD1000TMSC/LCD) under 200 g load and 15 s dwell time. The dry sliding friction test was performed on a disk friction and abrasion tester (Bruker/UMT-3) at room temperature. Each sample was carried out three friction tests to avoid error. Some errors that may affect the accuracy of test results have been noticed in advance, such as humidity, roughness and so on, and these errors have been eliminated as far as possible before the test. During the experiment, the counter-body was used a WC ball with a hardness of 1700 HV and a diameter of 9.5 mm. The applied load, sliding radius and wear time are 10 kg, 3 mm and
Flat plates of Ti6Al4V alloy with the dimension of 50 mm × 50 mm × 10 mm were cut as substrate for LSC processing. The surface to be laser cladding was polished to Ra 0.8 μm. Afterwards, Ti6Al4V alloy plates were washed with an ultrasonic cleaner in acetone. As shown in Table 1, the laser-clad materials used for LSC were Ni25 (chemical composition content of Ni25 was listed in Table 2), Si, pure Ti and nano-graphite powders. The three powder mixtures were thoroughly blended in ball mill for 2 h. Ni25 powder is a low hardness NiCr-B-Si self-melting alloy powder with good toughness and strong impact resistance. Ni and Ti have complete miscibility with each other, which forms TiNi, Ti2Ni intermetallic compounds. The TiNi-based intermetallic alloy has excellent tribological properties due to its many
Ni25
B
Fig. 1. Schematic of laser cladding process.
2. Experimental procedure
Powder mixtures No.
Composition
2
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clearly shows that no macroscopic cracks and pores are observed at the overlapping area surface of laser-clad coatings. Meanwhile, the surface color was changed to black as shown in Fig. 3, which is related to some chemical reactions induced by laser cladding. Fig. 4 displays the cross-sectional SEM views of single track of the three laser-clad Ni 25/Ti-Si-C system composite coatings respectively, using secondary electron image. Laser energy is absorbed by the powder through both powder coupling and bulk coupling mechanisms during the laser cladding process, directly [15]. As shown in Fig. 4, relatively smooth surfaces and metallurgical bonding to the Ti6Al4V substrate were obtained. However, obvious defect of holes were observed in the N1 coating and N3 coating. The reason for forming those holes in the coatings is that the moisture and air were mixed into the molten pool and reacted with graphite, in spite of some drying process have done to composite materials before argon protect in the laser cladding process. Moreover, due to the fast scanning speed let the molten pool flow is insufficient, resulting in the generated pores escaping. Fig. 5 shows XRD results of the three LSC composites coatings, depicting the presence of α-Ti, Ti3SiC2, Ti5Si3, TiC, TiNix intermetallic and γ-Ni solid solution is observed. As shown in the XRD patterns, it is because the decomposition temperature of SiC is lower than Ti3SiC2, the phase of SiC cannot be found, and the SiC would replace carbon react with Ti to form Ti3SiC2 by in situ synthesis in the laser molten pool. It is obviously that the diffraction peaks of Ti3SiC2 has elevated with the Ni25 content increased to 50%, the individual diffraction peak of Ti3SiC2 has the highest peak intensity when the Ti-Si-C composite powders content was 30% with the diffraction degree at 39.4°, which correspond as the peaks of Ti3SiC2 in the light of the JCPDS reference pattern card (No.00-048-1826 for Ti3SiC2). Unfortunately, it is difficult to accurately distinguish several overlapping diffraction peaks of TiC and Ti3SiC2. Fig. 6 shows the typical microstructure in the upper regions (a, b, c), intermediate regions (d, e, f) and bottom regions (g, h, i) of the N1, N2 and N3 LSC coatings and the EDS spot analysis of different metallographic morphologies in the coatings N2 and N3 are shown in Fig. 7 and corresponding element contents are listed in the Table 3. The EDS mapping of the element distribution of the intermediate region of the N2 coating has displayed in Fig. 8. The percentage of phases present in the Ti3SiC2/Ti5Si3/TiC/Ni-based composite coating N2 (50 wt% Ni25/ 50 wt% Ti-Si-C) distinguished by EBSD analyses is listed in Table 4 while the EBSD phase maps are shown in Fig. 9. It is worth noting that there is a significant difference in the cross-sectional microstructure of the coating along the depth direction. The grains in the upper part of the coating have great crystallite size, and more uniform dendrites are formed in the intermediate layer. The grains near the matrix are fine, and the equiaxed grains are mainly mixed with cell-dendrite morphology. Combining the XRD analysis in Fig. 5, with the EDS analysis in Table 3 and the EDS mapping in the Fig. 8, the dendrite-shaped (B) and (D) constituents were mainly composed of Ti and C elements and the atomic ratio nearly to 2:1, which should be eutectic structure with TiC and β-Ti (they were TiC and α-Ti at room temperature), Ti and nanographite powers were sectionally dissolved in molten pool during laser irradiation heating. The big black blocky (A) and (C) as shown in Fig. 7 (a) and (b) mainly consist of Ti, Si, C and Ni which are inference as composite Ti3SiC2 and TiNix intermetallic compound and some Ti5Si3 phase interspersed. The heat-affected zone (HAZ) as displayed in Fig. 6 (g) and (h), some white acicular martensite were distributed, the reason of this phenomenon is the Ti6Al4V substrate heated under laser beam, the temperature of the substrate increases to the phase transition temperature, and then the substrate is rapidly cooled, which is equivalent to a “quenching” process, and the α-Ti + β-Ti solid solution were converted into β-Ti solid solution, then the β-Ti phase transform to α-Ti phase incomplete due to the rapid cooling rate in this process, incomplete α-Ti phase and β-Ti solid solution can increase coating hardness effectively [21]. Furthermore, the EBSD analyses of the LSC
Fig. 2. Schematic of friction-wear tester.
30 min, respectively. The Fig. 2 shows the schematic diagram of friction and abrasion. Weight loss due to wear was measured using an electronic balance with an accuracy of 0.01 mg. Friction coefficient against sliding distance was obtained through online data acquisition system over the sliding distance. A post wear analysis of the worn out surfaces has been carried out to understand the wear mechanism of the coatings surface with the help of SEM micrograph. 3. Results and discussion 3.1. Microstructure of laser clad coatings The surface morphology observation of the laser-clad Ni25/Ti-Si-C composite coatings on Ti6Al4V substrate is shown in Fig. 3 with the corresponding mixed powder composition tabulated in Table 2. Unitary flat but local fluctuant cladding surfaces were generated for three kinds of Ni25/Ti-Si-C composite coatings, respectively. In addition, Fig. 3
Fig. 3. Surface morphology of the laser-clad Ni25/Ti-Si-C composite coatings: (a) coating N1, (b) coating N1 and (c) coating N3. 3
Optics and Laser Technology 126 (2020) 106077
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Fig. 4. Cross-sectional morphology of the laser-clad coatings: (a) N1 coating, (b) N2 coating and (c) N3 coating.
substrate. Accord with the phase distributions in the coatings, the average microhardness of N1, N2 and N3 coatings are 703.2 HV0.2, 751.9 HV0.2 and 850.6 HV0.2, respectively. There are several reasons for this phenomenon: amount of reinforced TiC, TiNix and Ti5Si3 were formed in time of the laser cladding process, the phase of TiC existing in the coatings as arborization, which played a role of supporting to enhance the microhardness of coatings [22]. Furthermore, the phase of Ti3SiC2 in-situ formation can also improve the mechanical properties of these coatings, since the Ti3SiC2 has both properties of ceramic and metallic materials [23].
3.3. Tribological behaviors and wear mechanisms Based on the results of our previous experiments [18], the change in surface roughness significantly affects the friction properties of the coating. Therefore, before the friction-wear test, samples to be tested had been polished the surface with sandpaper which avoids the impact of roughness on the wear resistance of coatings. The roughness of the coatings is measured by a 3D topograph (Rtec, USA) and the obtained roughness Ra is listed in Table 5. Fig. 11 displays the curves of friction coefficient for Ti6Al4V and the three composite coatings sliding against WC ball at room temperature. It is obvious that the LSC composite coatings exhibit considerably lower friction coefficient and better abrasion resistance than the Ti6Al4V titanium alloy. The average friction coefficient of N1, N2 and N3 coatings are around 0.46, 0.33 and 0.37, respectively, and that of the substrate is around 0.43. This shown that the frictional performance was improved by in-situ syntheses composite coatings. The wear profiles of LSC coatings and substrate after wear tests has been shown in Fig. 12, and the wear rate has been shown in Fig. 13. The wear rate of Ti6Al4V substrate and three coatings are 25.7 × 10−5 mm3 N−1 m−1, 22.6 × 10−5 mm3 N−1 m−1, 13.5 × 10−5 mm3 N−1 m−1 and 20.4 × 10−5 mm3 N−1 m−1, respectively. It is obviously that wear rate of three composite coatings are
Fig. 5. XRD patterns of LSC Ni25/Ti-Si-C composite coatings using Cu Kα radiation.
N2 coating is shown in Fig. 9. The results indicate that the mainly phases were NiTi2 and TiC, while the Ti3SiC2 and Ti5Si3 phases mainly existed in the boundary between NiTi2 and TiC. The percentage of Ti3SiC2 phase was 1.78% in the detection region of N2 coating. 3.2. Microhardness of the LSC coatings and tribological behaviors Microhardness profiles across the cross-section of the different composite coatings along the depth direction of coatings are shown in Fig. 10. It is obvious that there was a significant increase in microhardness compared to Ti6Al4V titanium alloy (approximately 360 HV0.2) and the hardness of three composite coatings revealed a downward trend from upper regions to the interface between coating and 4
Optics and Laser Technology 126 (2020) 106077
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Fig. 6. SEM micrographs at different regions of N1, N2 and N3 coatings: (a), (b) and (c) upper regions; (d), (e) and (f) intermediate regions; (g), (h) and (i) bottoms region.
lower compared with that of the substrate. Three kinds of composite coatings have better wear resistance. As the Fig. 12 shown, the wear track of substrate is deeper and wider than composite coatings. The promotion of wear resistance of three composite coatings is closely related to the evolution of microstructure due to the in-situ synthesis lubricant phase Ti3SiC2, hard ceramic phase TiC, silicide reinforcment Ti5Si3, Ti-Ni intermetallic and other phase distributed in the γ-Ni solid solution. matrix. The N2 coating has excellent self-lubricating and tribology properties compared to other coatings and substrates. To further characterize the in-situ syntheses ceramic phase on the tribological behavior of these composite coatings, SEM micrographs of worn surfaces are illustrated in Fig. 14. After the dry sliding wear test, the micro cracks formed between matrix and hard phases extended and under the alternating stress from the friction pair [24]. The wear debris,
Table 3 EDS analysis of different metallographic morphologies in coatings N2 and N3. Region
A B C D
Element composition/at. % Ti
Si
C
Al
Ni
V
77.49 64.57 73.7 59.63
2.62 – 2.05 –
0.89 33.87 0.88 39.98
10.62 1.56 12.16 –
5.33 – 7.34 –
3.05 – 3.87 0.4
spalling crater and deep furrow was generate in worn surface of substrate, in addition, serious plastic deformation can be observed on the worn surface (shown in Fig. 14(a)). Because of the low hardness of
Fig. 7. EDS spot analysis in the coatings: (a) coating N2, (b) coating N3. 5
Optics and Laser Technology 126 (2020) 106077
H. Yan, et al.
Fig. 8. EDS map scanning of the element distribution in the intermediate region of the N2 coating: (a) SEM micrograph, (b) Al element, (c) C element, (d) Ni element, (e) Si element, (f) Ti element, (g) V element. Table 4 Phase constitution of coating N2 by EBSD analysis (wt. %). Materials
Ti5Si3
Ti3SiC2
TiC
NiTi2
Zero analytic
Multiple coatings
2.19
1.78
28.63
51.75
15.65
substrate (approximately 360 HV0.2), the hard counterpart can push into the contact surface matrix, and it is speculated that the substrate suffered severe abrasive wear and plastic deformation. The worn surface of N1 coating is relatively smooth with some spalling craters and patches. Compare with the substrate, the N1 coating exhibit similar friction coefficient but lesser wear rate which indicates that N1 coating has the stronger wear resistance than the Ti6Al4V titanium alloy, and the wear mechanism of N1 coating is adhesive wear and abrasive wear. The worn surface of N2 coating was very smooth expect for little wear debris and patches with no spalling crater and furrow, as shown in Fig. 14 (c), there should be lubricating films formed between the coating and the counterpart at the dry sliding wear process [25,26], which provided strong support for N2 composite coating, and this are attributed to the entity of a large number of self-lubricating phase (Ti3SiC2 and Ti5Si3). Furthermore, the formation and spread out of transfer films which can prevent the coating and WC ball form further wear [1], and the primary wear mechanisms of N2 coating are small amount of adhesive wear and plastic deformation. There are certain
Fig. 9. EBSD phases maps of the LSC N2 coating.
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Fig. 10. Microhardness profiles of N1, N2, N3 coatings.
Fig. 12. Wear profiles of substrate, N1, N2 and N3 coatings after dry sliding wear test at room temperature for 30 min.
Table 5 Surface roughness of the LSC coatings. Number
Ra (μm)
N1 N2 N3
0.147 0.137 0.133
Fig. 13. The average wear rates of substrate, N1, N2 and N3 coatings after dry sliding wear test at room temperature for 30 min.
(2) During the laser cladding processing, in-situ chemical reactions occurred among elements Ti, Si and C (nano-graphite) in the laser molten pool. The composite coatings primarily incorporate continuous matrix α-Ti, Ti3SiC2, Ti5Si3, TiC, TiNix intermetallic compound and γ-Ni solid solution. (3) Compared with the Ti6Al4V substrate (approximately 0.43), the friction coefficient of Ti3SiC2/Ti5Si3/TiC/Ni-based composite coatings have been reduced due to the self-lubricating phase of Ti3SiC2 and ceramics Ti5Si3 and TiC. The composite coatings characterized by small amount of adhesive wear, plastic deformation and relatively smooth wear surface could be observed.
Fig. 11. The changes in friction coefficient with the sliding time of the three coatings and Ti6Al4V.
amount of spalling craters and wear debris with some scratches on the N3 coating worn surface, this shows that the N3 coating has suffered abrasive wear and adhesive wear while it has shown the well-deserved tribological properties and wear resistance. Combining with the coefficient of friction curve (as shown in Fig. 11), wear profile curve (as shown in Fig. 12), wear rate (as shown in Fig. 13) and SEM photographs of worn surface of N2 coating (as shown in Fig. 14(c)), there is no doubt that the N2 composite has the lowest friction coefficient and the lowest wear rate, represented excellent tribological properties.
CRediT authorship contribution statement Hua Yan: Writing - original draft. Kaiwei Liu: Writing - review & editing. Peilei Zhang: Data curation. Jian Zhao: Formal analysis. Yang Qin: Investigation, Methodology. Qinghua Lu: Conceptualization. Zhishui Yu: Supervision, Validation.
4. Conclusions (1) Ni-based metal matrix self-lubricating coatings containing solidlubricant phase Ti3SiC2, ceramic reinforced phase TiC and silicide reinforcement Ti5Si3 were successfully fabricated on Ti6Al4V surface by LSC from Ti-Si-C system and NiCrBSi with use of 5 kW fiber laser beam with 3 mm spot.
Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper. 7
Optics and Laser Technology 126 (2020) 106077
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Fig. 14. SEM micrographs of the worn surfaces on TI6AL4V substrate and composite coatings: (a) TV4 substrate; (b) N1 coating; (c) N2 coating; (d) N3 coating.
Acknowledgments
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This work was supported by the National Natural Science Foundation of China (51405288, 51605276, 51905332), Shanghai Science and Technology Committee Innovation Grant (17JC1400600, 17JC1400601), Local College Capacity Building of Shanghai Science and Technology Committee Innovation Programs (19030501300), High-tech projects of Shanghai Science and Technology Committee Innovation Programs (19511106402), Karamay Science and Technology Major Project (2018ZD002B), Aid for Xinjiang Science and Technology Project (2019E0235). References [1] Y.H. Lv, J. Li, Y.F. Tao, L.F. Hu, High-temperature wear and oxidation behaviors of TiNi/ Ti2Ni matrix composite coatings with TaC addition prepared on Ti6Al4V by laser cladding, Appl. Surf. Sci. 402 (2017) 478–494. [2] Salih Durdu, Ömer Faruk Deniz, Işıl Kutbay, Metin Usta, Characterization and formation of hydroxyapatite on Ti6Al4V coated by plasma electrolytic oxidation, J. Alloy. Compd. 551 (2013) 422–429, https://doi.org/10.1016/j.jallcom.2012.11.024. [3] Ruidi Li, Pengda Niu, Tiechui Yuan, Peng Cao, Chao Chen, Kechao Zhou, Selective laser melting of an equiatomic CoCrFeMnNi high-entropy alloy: Processability, non-equilibrium microstructure and mechanical property, J. Alloy. Compd. 746 (2018) 125–134. [4] Hu. Tianchang, Hu. Litian, Qi Ding, Effective solution for the tribological problems of Ti6Al-4V: Combination of laser surface texturing and solid lubricant film, Surf. Coat. Technol. 206 (2012) 5060–5066. [5] Liuyang Fang, Hua Yan, Yansong Yao, Peilei Zhang, Qiushi Gao, Yang Qin. Reactive fabrication and effect of NbC on microstructure and tribological properties of CrS Cobased self-lubricating coatings by laser cladding. Materials, 11(2018), 44. [6] G.F. Sun, R. Zhou, Y.K. Zhang, G.D. Yuan, K. Wang, X.D. Ren, D.P. Wen, Microstructure evolution and lubricant wear performance of laser alloyed layers on automobile engine chains, Opt. Laser Technol. 62 (2014) 20–31. [7] Yong-Jie Zhai, Xiu-Bo Liu, Shi-Jie Qiao, Ming-Di Wang, Lu. Xiao-Long, YongGuang Wang, Yao Chen, Li-Xia Ying, Characteristics of laser clad α-Ti/TiC+(Ti, W)C1–x/ Ti2SC+TiS composite coatings on TA2 titanium alloy, Opt. Laser Technol. 89 (2017) 97–107. [8] Qiushi Gao, Hua Yan, Yang Qin, Peilei Zhang, Jialong Guo, Zhengfei Chen, Zhishui Yu, Laser cladding Ti-Ni/TiN/TiW+TiS/WS2 self-lubricating wear resistant composite coating on Ti-6Al-4V alloy, Opt. Laser Technol. 113 (2019) 182–191, https://doi.org/10. 1016/j.optlastec.2018.12.046. [9] Y.H. Xia, Y. Wang, Z.W. Yang, D.P. Wang, Contact-reactive brazing of Ti3SiC2, ceramic to TC4 alloy using a Ni interlayer: Interfacial microstructure and joining properties, Ceram. Int. 44 (2018) 11869–11877. [10] M.Z. Sun, Progress in research and development on MAX phases: a family of layered ternary compounds, Int. Mater. Rev. 56 (2011) 143–166.
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Fabrication and tribological behaviors of Ti3SiC2/Ti5Si3/TiC/Ni-based composite coatings by laser cladding for self-lubricating applications
T
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Hua Yan , Kaiwei Liu, Peilei Zhang, Jian Zhao, Yang Qin, Qinghua Lu, Zhishui Yu School of Materials Engineering, Shanghai University of Engineering Science, Shanghai 201620, PR China Shanghai Collaborated Innovation Center of Laser Advanced Manufacturing Technology, Shanghai 201620, PR China
H I GH L IG H T S
(Ti SiC ) and Ti Si silicide composite coatings were successfully prepared by in-situ synthesis laser cladding. • MAX self-lubricating properties of the coatings are attributed to Ti SiC , Ti Si and TiC. • Excellent • Laser-clad Ti SiC /Ti Si /TiC/Ni-based composite coatings exhibit small amount of adhesive wear, plastic deformation. 3
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A R T I C LE I N FO
A B S T R A C T
Keywords: Ti-Si-C Laser cladding In-situ reaction Ti3SiC2 Self-lubricating
In the work the in-situ synthesis of Ti3SiC2 (MAX) phase and silicide reinforced Ni-based composite self-lubricating coatings from Ti-Si-C system and NiCrBSi powders were carried and initiated by laser cladding with use of 5 kW fiber laser beam with 3 mm spot. The microstructures of the laser-clad in situ synthetic self-lubricating coatings were analyzed by a scanning electron microscope (SEM) equipped with an X-ray energy dispersive spectrometer (EDS). An X-ray diffraction (XRD) spectrometer and an electron back-scattered diffraction (EBSD) were used for determination of the reaction products in the composite coatings. The friction and abrasion behavior of the coatings were evaluated at room temperature by a dry sliding friction tester. The results indicate that in-situ chemical reactions took place between elements Ti, Si and C in the laser molten pool, and the reaction products included Ti3SiC2, Ti5Si3, and TiC ceramics as well as TiNix compound. Finally, three laser-clad Ti3SiC2/Ti5Si3/TiC/Ni-based composite coatings with the total thickness about 1 mm were fabricated on Ti6Al4V alloy. The average microhardness of the three coatings was 703.2 HV0.2, 751.9 HV0.2 and 850.6 HV0.2 respectively, which has been significantly improved, compared with the hardness of Ti6Al4V substrate (about 360 HV0.2). The average friction coefficient of the Ti3SiC2/Ti5Si3/TiC/Ni-based composite coating (50 wt% Ni25/50 wt% Ti-Si-C) reduced to 0.33 at room temperature, and it exhibited the wear rate of 13.5 × 10−5 mm3 N−1 m−1. The laser cladding Ti3SiC2/Ti5Si3/TiC/Ni-based composite coatings characterized by small amount of adhesive wear, plastic deformation and relatively smooth wear surface could be observed.
1. Introduction Titanium alloys are very important material and widely used in aerospace, biomedical and automatic products due to their excellent inherent properties such as superior strength-to-weight ratio, good heat resistance and excellent corrosion resistance [1,2]. Nevertheless, the application of titanium alloys in friction drive mechanism, especially as a wear resistant rotating part has been severe limitation in the application of key coupling piece because of its low hardness, high friction coefficient, poor wear resistance and low oxidation resistance at high temperature [3,4]. Generally speaking, the failure of working parts
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starts forms their surfaces, where the part is more susceptible to failure under corrosion and wears conditions [5]. Therefore, there is an active demand in industrial production to improve the surface wear behavior including poor wear resistance and low hardness. For the past few years, laser surface cladding (LSC) has favorable characteristics, such as well metallurgical bond between substrate and coating, low dilution rate, high cooling rate, high dense microstructure. Due to the satisfactory characteristics, LSC has been widely used to manufacture composite coatings owning high hardness and outstanding tribological properties [6,7]. Significant processes of LSC have been made on improving abrasion resistance of Ti6Al4V to prepare metal matrix composites
Corresponding author at: School of Materials Engineering, Shanghai University of Engineering Science, Shanghai 201620, PR China. E-mail addresses: [email protected], [email protected] (H. Yan).
https://doi.org/10.1016/j.optlastec.2020.106077 Received 21 October 2019; Received in revised form 3 January 2020; Accepted 13 January 2020 0030-3992/ © 2020 Elsevier Ltd. All rights reserved.
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(MMC) reinforced by the ceramic particles and solid lubricants [8]. The Ti3SiC2 is one of the best-characterized Mn+1AXn phases (where M is an early transition metal, A is a group 13–16 element, X is either C or N). It has excellent high temperature high thermal shock resistance and strength and was first synthesized by W. Jeitschko and H. Nowotny [9–11]. Ti3SiC2 is famous as a new type ceramic has a hexagonal crystalline lattice and the crystalline structure shows a typical laminate characteristic, which has the properties of metal materials and ceramic, such as high thermal stability, high melting point, good self-lubricity and excellent electrical and thermal conductivities [12,13]. Hai [14] et al. investigated the friction and wear of self-mated Ti3SiC2 under unlubricated condition and lubrication of PbO powders at different temperatures. They found that the microstructure and chemical composition have a strong effect on the friction and wear of self-mated Ti3SiC2 under lubrication of PbO powders. Aiming at improving the wear resistance of 35CrMo steel, Li [15] et al also fabricated Ti3SiC2/ Co-based composites coatings on 35CrMo steel by LSC. Experimental results showed that Ti3SiC2 partially dissolved to form TiC. The microhardness of the coatings was significantly enhanced, which was at least 2.3 times that of substrate. Recently, design and preparation of Ti6Al4V/Ti-Si-C system functional gradient material (FGM) as well as the related principle were studied by Li et al [16]. Their research results indicate that in-situ chemical reactions took place between elements Ti, Si and C in the deposited layers, and the reaction products included TiC and Ti3SiC2 ceramics as well as Ti5Si3 compound. In the literature there are negligible information concerning LSC synthesis of Ti3SiC2 phase on Ti6Al4V surface to improve its tribological properties. It is worth to pay attention to that the high energy density and concentricity of laser beam will lead Ti3SiC2 or other solid lubricant and influence the practicality of laser cladding self-lubricating composite coatings in industrial production [17]. To the best knowledge of authors, there is little information available in the literature about the synthesis of Ti3SiC2 coating on Ti6Al4V substrate using LSC technique. In this work, the objective is focusing on the in-situ reaction synthesis to fabricate the self-lubricating composite coatings that contains solid-lubricant phase Ti3SiC2 and silicide reinforcement, as well as exploring the idea that Ti3SiC2 and silicide reinforced particles contribute to improving the microstructural evolution of the coatings. In addition, the tribological behavior and wear mechanisms of LSC self-lubricating coatings from NiCrBSi/Ti-Si-C system (Ti powder, Si powder and nano graphite) were also discussed.
Table 2 Compositions of Ni25 powders (wt. %).
Table 1 Powder mixtures used for LSC.
N1 N2 N3
Components (wt. %) Ti
Si
Nano-graphite
30 50 70
49.98 28.56 21.42
11.69 6.68 5.01
8.33 4.76 3.57
C
Si
Fe
Ni
Content
1.75
0.06
6.91
0.26
Bal.
superior properties, such as pseudo-elasticity toughness and ductility as in our previous research papers [18]. The Ti-Si-C system powders molar ratio of Ti powder, Si powder and nano-graphite was 3:1.2:2. The mass ratios of Ni25 and Ti-Si-C were 3:7, 5:5 and 7:3, respectively. The mixed composite powders were preliminarily placed on the Ti6Al4V alloy by an organic binder with a thickness of 1.5 mm as our previous studies [18–20], and then oven dried before LSC. Powder mixtures were designated as N1, N2 and N3 coatings as in Table 1. The LSC experiment was carried out using an IPG-YLS-5000 fiber laser system with an inert gas protection device which is shown in Fig. 1. The optimized parameters utilized in the experiments are as follows: laser power 1.8 kW, scanning speed 15 mm/s, and spot diameter 3 mm. Argon was selected as the protective gas with a flow rate 10 L/min. The protective gas was switched on three seconds before laser cladding procedure until three seconds after the procedure finished. Then the single track and overlapped coatings with an overlap rate of 40% were cooled in air. After laser cladding, the test samples were cut by wire cut electric discharge machine for microstructure observation and friction-wear testing. A detailed characterization of the composite coatings in terms of microstructure, phases, microhardness, wear resistance and coefficient friction have been undertaken and the effect of precursor powder composition were studied. The cross-sections of the samples were prepared for microstructure analyses. X-ray diffraction (XRD) test (Cu Kα, 1.54 Å wavelength radiations) was employed to identify the phases of the coatings by an X'Pert PRO X-ray Generator machine. Scanning electron-microscopy (Hitachi/S-3400) with energy dispersive spectroscopy (EDS) were used to study the microstructure and to characterize the elemental distribution in a semiquantitative manner. Microhardness at the cross-section of the coatings was measured with Vicker microhardness testing machine (HXD1000TMSC/LCD) under 200 g load and 15 s dwell time. The dry sliding friction test was performed on a disk friction and abrasion tester (Bruker/UMT-3) at room temperature. Each sample was carried out three friction tests to avoid error. Some errors that may affect the accuracy of test results have been noticed in advance, such as humidity, roughness and so on, and these errors have been eliminated as far as possible before the test. During the experiment, the counter-body was used a WC ball with a hardness of 1700 HV and a diameter of 9.5 mm. The applied load, sliding radius and wear time are 10 kg, 3 mm and
Flat plates of Ti6Al4V alloy with the dimension of 50 mm × 50 mm × 10 mm were cut as substrate for LSC processing. The surface to be laser cladding was polished to Ra 0.8 μm. Afterwards, Ti6Al4V alloy plates were washed with an ultrasonic cleaner in acetone. As shown in Table 1, the laser-clad materials used for LSC were Ni25 (chemical composition content of Ni25 was listed in Table 2), Si, pure Ti and nano-graphite powders. The three powder mixtures were thoroughly blended in ball mill for 2 h. Ni25 powder is a low hardness NiCr-B-Si self-melting alloy powder with good toughness and strong impact resistance. Ni and Ti have complete miscibility with each other, which forms TiNi, Ti2Ni intermetallic compounds. The TiNi-based intermetallic alloy has excellent tribological properties due to its many
Ni25
B
Fig. 1. Schematic of laser cladding process.
2. Experimental procedure
Powder mixtures No.
Composition
2
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clearly shows that no macroscopic cracks and pores are observed at the overlapping area surface of laser-clad coatings. Meanwhile, the surface color was changed to black as shown in Fig. 3, which is related to some chemical reactions induced by laser cladding. Fig. 4 displays the cross-sectional SEM views of single track of the three laser-clad Ni 25/Ti-Si-C system composite coatings respectively, using secondary electron image. Laser energy is absorbed by the powder through both powder coupling and bulk coupling mechanisms during the laser cladding process, directly [15]. As shown in Fig. 4, relatively smooth surfaces and metallurgical bonding to the Ti6Al4V substrate were obtained. However, obvious defect of holes were observed in the N1 coating and N3 coating. The reason for forming those holes in the coatings is that the moisture and air were mixed into the molten pool and reacted with graphite, in spite of some drying process have done to composite materials before argon protect in the laser cladding process. Moreover, due to the fast scanning speed let the molten pool flow is insufficient, resulting in the generated pores escaping. Fig. 5 shows XRD results of the three LSC composites coatings, depicting the presence of α-Ti, Ti3SiC2, Ti5Si3, TiC, TiNix intermetallic and γ-Ni solid solution is observed. As shown in the XRD patterns, it is because the decomposition temperature of SiC is lower than Ti3SiC2, the phase of SiC cannot be found, and the SiC would replace carbon react with Ti to form Ti3SiC2 by in situ synthesis in the laser molten pool. It is obviously that the diffraction peaks of Ti3SiC2 has elevated with the Ni25 content increased to 50%, the individual diffraction peak of Ti3SiC2 has the highest peak intensity when the Ti-Si-C composite powders content was 30% with the diffraction degree at 39.4°, which correspond as the peaks of Ti3SiC2 in the light of the JCPDS reference pattern card (No.00-048-1826 for Ti3SiC2). Unfortunately, it is difficult to accurately distinguish several overlapping diffraction peaks of TiC and Ti3SiC2. Fig. 6 shows the typical microstructure in the upper regions (a, b, c), intermediate regions (d, e, f) and bottom regions (g, h, i) of the N1, N2 and N3 LSC coatings and the EDS spot analysis of different metallographic morphologies in the coatings N2 and N3 are shown in Fig. 7 and corresponding element contents are listed in the Table 3. The EDS mapping of the element distribution of the intermediate region of the N2 coating has displayed in Fig. 8. The percentage of phases present in the Ti3SiC2/Ti5Si3/TiC/Ni-based composite coating N2 (50 wt% Ni25/ 50 wt% Ti-Si-C) distinguished by EBSD analyses is listed in Table 4 while the EBSD phase maps are shown in Fig. 9. It is worth noting that there is a significant difference in the cross-sectional microstructure of the coating along the depth direction. The grains in the upper part of the coating have great crystallite size, and more uniform dendrites are formed in the intermediate layer. The grains near the matrix are fine, and the equiaxed grains are mainly mixed with cell-dendrite morphology. Combining the XRD analysis in Fig. 5, with the EDS analysis in Table 3 and the EDS mapping in the Fig. 8, the dendrite-shaped (B) and (D) constituents were mainly composed of Ti and C elements and the atomic ratio nearly to 2:1, which should be eutectic structure with TiC and β-Ti (they were TiC and α-Ti at room temperature), Ti and nanographite powers were sectionally dissolved in molten pool during laser irradiation heating. The big black blocky (A) and (C) as shown in Fig. 7 (a) and (b) mainly consist of Ti, Si, C and Ni which are inference as composite Ti3SiC2 and TiNix intermetallic compound and some Ti5Si3 phase interspersed. The heat-affected zone (HAZ) as displayed in Fig. 6 (g) and (h), some white acicular martensite were distributed, the reason of this phenomenon is the Ti6Al4V substrate heated under laser beam, the temperature of the substrate increases to the phase transition temperature, and then the substrate is rapidly cooled, which is equivalent to a “quenching” process, and the α-Ti + β-Ti solid solution were converted into β-Ti solid solution, then the β-Ti phase transform to α-Ti phase incomplete due to the rapid cooling rate in this process, incomplete α-Ti phase and β-Ti solid solution can increase coating hardness effectively [21]. Furthermore, the EBSD analyses of the LSC
Fig. 2. Schematic of friction-wear tester.
30 min, respectively. The Fig. 2 shows the schematic diagram of friction and abrasion. Weight loss due to wear was measured using an electronic balance with an accuracy of 0.01 mg. Friction coefficient against sliding distance was obtained through online data acquisition system over the sliding distance. A post wear analysis of the worn out surfaces has been carried out to understand the wear mechanism of the coatings surface with the help of SEM micrograph. 3. Results and discussion 3.1. Microstructure of laser clad coatings The surface morphology observation of the laser-clad Ni25/Ti-Si-C composite coatings on Ti6Al4V substrate is shown in Fig. 3 with the corresponding mixed powder composition tabulated in Table 2. Unitary flat but local fluctuant cladding surfaces were generated for three kinds of Ni25/Ti-Si-C composite coatings, respectively. In addition, Fig. 3
Fig. 3. Surface morphology of the laser-clad Ni25/Ti-Si-C composite coatings: (a) coating N1, (b) coating N1 and (c) coating N3. 3
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Fig. 4. Cross-sectional morphology of the laser-clad coatings: (a) N1 coating, (b) N2 coating and (c) N3 coating.
substrate. Accord with the phase distributions in the coatings, the average microhardness of N1, N2 and N3 coatings are 703.2 HV0.2, 751.9 HV0.2 and 850.6 HV0.2, respectively. There are several reasons for this phenomenon: amount of reinforced TiC, TiNix and Ti5Si3 were formed in time of the laser cladding process, the phase of TiC existing in the coatings as arborization, which played a role of supporting to enhance the microhardness of coatings [22]. Furthermore, the phase of Ti3SiC2 in-situ formation can also improve the mechanical properties of these coatings, since the Ti3SiC2 has both properties of ceramic and metallic materials [23].
3.3. Tribological behaviors and wear mechanisms Based on the results of our previous experiments [18], the change in surface roughness significantly affects the friction properties of the coating. Therefore, before the friction-wear test, samples to be tested had been polished the surface with sandpaper which avoids the impact of roughness on the wear resistance of coatings. The roughness of the coatings is measured by a 3D topograph (Rtec, USA) and the obtained roughness Ra is listed in Table 5. Fig. 11 displays the curves of friction coefficient for Ti6Al4V and the three composite coatings sliding against WC ball at room temperature. It is obvious that the LSC composite coatings exhibit considerably lower friction coefficient and better abrasion resistance than the Ti6Al4V titanium alloy. The average friction coefficient of N1, N2 and N3 coatings are around 0.46, 0.33 and 0.37, respectively, and that of the substrate is around 0.43. This shown that the frictional performance was improved by in-situ syntheses composite coatings. The wear profiles of LSC coatings and substrate after wear tests has been shown in Fig. 12, and the wear rate has been shown in Fig. 13. The wear rate of Ti6Al4V substrate and three coatings are 25.7 × 10−5 mm3 N−1 m−1, 22.6 × 10−5 mm3 N−1 m−1, 13.5 × 10−5 mm3 N−1 m−1 and 20.4 × 10−5 mm3 N−1 m−1, respectively. It is obviously that wear rate of three composite coatings are
Fig. 5. XRD patterns of LSC Ni25/Ti-Si-C composite coatings using Cu Kα radiation.
N2 coating is shown in Fig. 9. The results indicate that the mainly phases were NiTi2 and TiC, while the Ti3SiC2 and Ti5Si3 phases mainly existed in the boundary between NiTi2 and TiC. The percentage of Ti3SiC2 phase was 1.78% in the detection region of N2 coating. 3.2. Microhardness of the LSC coatings and tribological behaviors Microhardness profiles across the cross-section of the different composite coatings along the depth direction of coatings are shown in Fig. 10. It is obvious that there was a significant increase in microhardness compared to Ti6Al4V titanium alloy (approximately 360 HV0.2) and the hardness of three composite coatings revealed a downward trend from upper regions to the interface between coating and 4
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Fig. 6. SEM micrographs at different regions of N1, N2 and N3 coatings: (a), (b) and (c) upper regions; (d), (e) and (f) intermediate regions; (g), (h) and (i) bottoms region.
lower compared with that of the substrate. Three kinds of composite coatings have better wear resistance. As the Fig. 12 shown, the wear track of substrate is deeper and wider than composite coatings. The promotion of wear resistance of three composite coatings is closely related to the evolution of microstructure due to the in-situ synthesis lubricant phase Ti3SiC2, hard ceramic phase TiC, silicide reinforcment Ti5Si3, Ti-Ni intermetallic and other phase distributed in the γ-Ni solid solution. matrix. The N2 coating has excellent self-lubricating and tribology properties compared to other coatings and substrates. To further characterize the in-situ syntheses ceramic phase on the tribological behavior of these composite coatings, SEM micrographs of worn surfaces are illustrated in Fig. 14. After the dry sliding wear test, the micro cracks formed between matrix and hard phases extended and under the alternating stress from the friction pair [24]. The wear debris,
Table 3 EDS analysis of different metallographic morphologies in coatings N2 and N3. Region
A B C D
Element composition/at. % Ti
Si
C
Al
Ni
V
77.49 64.57 73.7 59.63
2.62 – 2.05 –
0.89 33.87 0.88 39.98
10.62 1.56 12.16 –
5.33 – 7.34 –
3.05 – 3.87 0.4
spalling crater and deep furrow was generate in worn surface of substrate, in addition, serious plastic deformation can be observed on the worn surface (shown in Fig. 14(a)). Because of the low hardness of
Fig. 7. EDS spot analysis in the coatings: (a) coating N2, (b) coating N3. 5
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Fig. 8. EDS map scanning of the element distribution in the intermediate region of the N2 coating: (a) SEM micrograph, (b) Al element, (c) C element, (d) Ni element, (e) Si element, (f) Ti element, (g) V element. Table 4 Phase constitution of coating N2 by EBSD analysis (wt. %). Materials
Ti5Si3
Ti3SiC2
TiC
NiTi2
Zero analytic
Multiple coatings
2.19
1.78
28.63
51.75
15.65
substrate (approximately 360 HV0.2), the hard counterpart can push into the contact surface matrix, and it is speculated that the substrate suffered severe abrasive wear and plastic deformation. The worn surface of N1 coating is relatively smooth with some spalling craters and patches. Compare with the substrate, the N1 coating exhibit similar friction coefficient but lesser wear rate which indicates that N1 coating has the stronger wear resistance than the Ti6Al4V titanium alloy, and the wear mechanism of N1 coating is adhesive wear and abrasive wear. The worn surface of N2 coating was very smooth expect for little wear debris and patches with no spalling crater and furrow, as shown in Fig. 14 (c), there should be lubricating films formed between the coating and the counterpart at the dry sliding wear process [25,26], which provided strong support for N2 composite coating, and this are attributed to the entity of a large number of self-lubricating phase (Ti3SiC2 and Ti5Si3). Furthermore, the formation and spread out of transfer films which can prevent the coating and WC ball form further wear [1], and the primary wear mechanisms of N2 coating are small amount of adhesive wear and plastic deformation. There are certain
Fig. 9. EBSD phases maps of the LSC N2 coating.
6
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Fig. 10. Microhardness profiles of N1, N2, N3 coatings.
Fig. 12. Wear profiles of substrate, N1, N2 and N3 coatings after dry sliding wear test at room temperature for 30 min.
Table 5 Surface roughness of the LSC coatings. Number
Ra (μm)
N1 N2 N3
0.147 0.137 0.133
Fig. 13. The average wear rates of substrate, N1, N2 and N3 coatings after dry sliding wear test at room temperature for 30 min.
(2) During the laser cladding processing, in-situ chemical reactions occurred among elements Ti, Si and C (nano-graphite) in the laser molten pool. The composite coatings primarily incorporate continuous matrix α-Ti, Ti3SiC2, Ti5Si3, TiC, TiNix intermetallic compound and γ-Ni solid solution. (3) Compared with the Ti6Al4V substrate (approximately 0.43), the friction coefficient of Ti3SiC2/Ti5Si3/TiC/Ni-based composite coatings have been reduced due to the self-lubricating phase of Ti3SiC2 and ceramics Ti5Si3 and TiC. The composite coatings characterized by small amount of adhesive wear, plastic deformation and relatively smooth wear surface could be observed.
Fig. 11. The changes in friction coefficient with the sliding time of the three coatings and Ti6Al4V.
amount of spalling craters and wear debris with some scratches on the N3 coating worn surface, this shows that the N3 coating has suffered abrasive wear and adhesive wear while it has shown the well-deserved tribological properties and wear resistance. Combining with the coefficient of friction curve (as shown in Fig. 11), wear profile curve (as shown in Fig. 12), wear rate (as shown in Fig. 13) and SEM photographs of worn surface of N2 coating (as shown in Fig. 14(c)), there is no doubt that the N2 composite has the lowest friction coefficient and the lowest wear rate, represented excellent tribological properties.
CRediT authorship contribution statement Hua Yan: Writing - original draft. Kaiwei Liu: Writing - review & editing. Peilei Zhang: Data curation. Jian Zhao: Formal analysis. Yang Qin: Investigation, Methodology. Qinghua Lu: Conceptualization. Zhishui Yu: Supervision, Validation.
4. Conclusions (1) Ni-based metal matrix self-lubricating coatings containing solidlubricant phase Ti3SiC2, ceramic reinforced phase TiC and silicide reinforcement Ti5Si3 were successfully fabricated on Ti6Al4V surface by LSC from Ti-Si-C system and NiCrBSi with use of 5 kW fiber laser beam with 3 mm spot.
Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper. 7
Optics and Laser Technology 126 (2020) 106077
H. Yan, et al.
Fig. 14. SEM micrographs of the worn surfaces on TI6AL4V substrate and composite coatings: (a) TV4 substrate; (b) N1 coating; (c) N2 coating; (d) N3 coating.
Acknowledgments
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