Effects of friction layer characteristics on the

Materials Research Express

PAPER

Effects of friction layer characteristics on the tribological properties of Ni3Al solid-lubricating composites at different load conditions To cite this article: Guanchen Lu et al 2018 Mater. Res. Express 5 056527

View the article online for updates and enhancements.

This content was downloaded from IP address 218.197.142.133 on 25/05/2018 at 10:59

Mater. Res. Express 5 (2018) 056527

https://doi.org/10.1088/2053-1591/aac41f

PAPER

RECEIVED

17 April 2018 REVISED

1 May 2018 ACCEPTED FOR PUBLICATION

11 May 2018

Effects of friction layer characteristics on the tribological properties of Ni3Al solid-lubricating composites at different load conditions Guanchen Lu1, Xiaoliang Shi1 , Yuchun Huang1, Xiyao Liu1 and Meijun Yang2 1

PUBLISHED

25 May 2018

2

School of Mechanical and Electronic Engineering, Wuhan University of Technology, 122 Luoshi Road, Wuhan 430070, People’s Republic of China The Center for Materials Research and Analysis, Wuhan University of Technology, 122 Luoshi Road, Wuhan 430070, People’s Republic of China

E-mail: [email protected] Keywords: solid-lubrication material, tribological behaviors, multi-layer graphene, wear scars

Abstract This paper investigates the effects of friction layer characteristics of Ni3Al matrix self-lubricating composites (NMCs) on the tribological properties sliding against ceramic ball Si3N4 at dry friction process at the different load conditions. The characteristics of friction layer are performed in terms of hardness of wear scars, thickness and elemental distributions of friction layer. The results show that the microhardness of wear scars of NMCs increases with the increase of the sliding time and applied load, which results in friction coefficient reduced and wear rate decreased, indicating that the tribological performance of NMCs is obviously affected by microhardness of wear scar. However, under excessive applied load, the performance of friction layer of NMCs is deteriorated for the spalling of wear debris and deformation of contact surface. Therefore, selecting appropriate load conditions during the sliding contact, at the transition to the optimal properties of friction layer maybe occur. NMCs exhibits excellent tribological properties at 15N, which leads to the lowest friction coefficient (0.386) and wear rate (2.48×10−5 mm3 N−1 m−1), as well as the smoothest surface of wear track compared with the other load conditions. Meanwhile, the elemental distributions analysis of crosssection of friction layer of NMCs shows that the frictional structures can be divided into three main layers. The thickness of the friction-affected layer varies with the changing of applied load. These results could provide a reference for preparing the solid-lubrication materials with better tribological properties.

1. Introduction Friction and wear behaviors of metal matrix composites (MMCs) have been easily observed in the mechanical assemblies and facilities [1, 2]. The worn surfaces of MMCs used in mechanical devices in the friction process could result in the significant structural modifications. Friction layer structures formed include lots of frictional features and have a great influence on the tribological properties of materials. Investigations of tribological properties of frictional structure formed by friction and wear behaviors have been widely proposed [3, 4]. A Moshkovich et al [5] analyzed the friction layer structures of copper under the different loads and sliding speeds. The results indicated that frictional characteristic of Cu under lubricated conditions is the layered lamellar structures formed in the direction of friction. Similarly, Tarasov S et al [6] studied the microstructure and mechanical properties of nano-crystalline copper layer generated by rubbing. The results reported that there were four different friction-affected layers formed along the longitudinal cross-sections of specimens below the worn surface. Indeed, with the development of microscopic testing techniques and the progress on tribology, the research on the tribological behavior of materials has been studied from the macroscopic analysis in the early to the microscopic mechanism in order to reveal the change of the microstructure and physico-chemical properties of materials. Obviously, the microstruture of plastic deformation of worn surface has a great influence on the © 2018 IOP Publishing Ltd


G Lu et al

tribological property of material. The worn surface pattern formed on the faces of the copper matrix under the heavy applied load and the contacted surface of the counter-body were investigated by Tarasov S Y et al [7]. Ma et al [8] investigated the testing methods of friction coefficient and wear rate for analyzing morphological changes of materials at the condition of high strain rate. It proved that grain refinement was also caused during the severe plastic deformation processes [9, 10]. The changes of frictional structure during dry sliding process lead to the formation of the friction layer, which plays an important role in the anti-friction and anti-wear property of the self-lubrication materials. The plastic deformations of worn surface and subsurface during the friction process result in the formation of a frictional structure, which consists of a sequence of phenomena, such as surface hardening, grain refinement below worn surface and oxidation reaction, etc. The structural deformations of subsurface layers during the sliding friction has been studied by many researchers [11, 12]. Li et al [13] investigated the influences of grain size and substrate hardness on the tribological performance of solution annealed Nickel-based metals fretting under fretting condition. The results indicated that solution annealing temperature had a great influence on grain size and substrate hardness of Nickel-based metals. The grain size increased with the increase of the temperature, whereas the hardness decreased. Zhai et al [14] designed a large number of experiments to explain the effect of hardness ratio on the friction and wear behaviors at different sliding velocities. It can be found that the thick friction layer below the worn surface could influence the friction coefficient and wear volume. The increased hardness in the subsurface by strain hardening also had an effect on the improvement of wear resistance. Although the microstructure and property evolution of frictional structure of self-lubrication composites currently researched by some scientists has made some progress, the systematic knowledge between the tribological property and frictional structure has not been established yet. Especially, the deformed process of worn surface influenced by the coupling of friction heat and shear stress produced by heavy applied load during the dry sliding friction process has not been analyzed clearly. Moreover, the microhardness of wear surface will also change because of the effect of gradient temperature and stress so as to affect the wear behaviors. Therefore, the effect of the hardness varies and microstructure of worn surface induced by friction and wear behavior on the tribological property still need be further explored. Ni3Al metal matrix composites have been widely investigated as important engineering materials owing to their unique properties in the industrial applications, such as corrosion-resisting, oxidationresisting, shape memory as well as high melting temperature and high hardness [15, 16]. They have been gradually put into practical application such as turbine blade, valve-seat, cutting tools, and mechanical fixtures [17]. The poor wear and corrosion resistance of Ni3Al metal parts limits their wide applications in harsh environments. The systematic study of the relationship between wear mechanism and tribological properties of Ni3Al matrix composites undoubtedly helps to correctly understand the friction and wear behavior and prepare the self-lubricating composites. Accordingly, the main objective of the present work is to investigate the effects of the structure and morphologies of friction layer of Ni3Al matrix self-lubricating composites (NMCs) on the tribological properties sliding against ceramic ball Si3N4 at dry friction tests under different applied loads. The multi-layer graphene (MLG) because of behaviors of diffusion and migration in the matrix at the load conditions [18–20] particles were added into Ni3Al matrix composites to investigate microstructural evolution of worn surfaces and in the subsurface. The effects of hardness of wear scars, thickness and elemental distributions of friction layer under different contact applied loads on the tribological properties of Ni3Al matrix composites are investigated, and the corresponding wear characteristics of materials are also discussed.

2. Experimental details Ni3Al metal matrix composites, which were composed of commercially available Ni, Al, Cr, Mo and Zr powders. Powders of MLG provided by Nanjing XFNANO material Tech Co., Ltd are chosen to be added into Ni3Al alloys. Firstly, the mixed powders were milled uniformly in a stainless steel container at 120 rpm in vacuum for 6 h. Then, the mixed powders were sintered by spark plasma sintering (SPS). The compaction of the composite powders was carried out in graphite die at a pressure of 30 MPa and a temperature of 1150 °C in pure Ar atmosphere protection, maintained for 30 min. The heating rate of temperature was 100 °C·min−1. The asfabricated samples were removed the graphite layer and machined into standard sizes. Finally, the as-prepared samples are polished with metallographic papers down to 1200 grit, and then with 0.5 μm wet polishing diamond pastes. The dry sliding tests were performed using a home-built ball-on-disk high-temperature tribometer with rotational sliding mode (made in Zhong Ke Kai Hua Corporation, China). A basic sketch of the ball-on-disk device is displayed in figure 1. The counterpart ball is a commercially available ceramic ball of Si3N4. Its hardness is 15.0 GPa, and surface roughness is about 0.01 μm. In the schematic diagram, F stands for the applied load of the ball. The selected applied loads are 5, 10, 15, and 20N, respectively. The sliding speed is 0.2 m s−1 and the 2


G Lu et al

Figure 1. Sketch of ball-on-disk. The diameter of the pin (ball) was 6 mm; the dimensions of the disk were 250 mm (diameter) by 5 mm (height).

Figure 2. Hardness measured locations of the tested sample.

sliding time is 30 min. After the tests, the samples were taken out from the tribometer to measure wear volumes and calculate the wear rates. The wear rate (W) is calculated on the basis of the formula (2-1): W=

V V´r = S´F S´F´r

(2-1)

Where V is the wear volume loss(mm3), S is the sliding distance (m) and F is the applied load (N). The hardness of as-prepared samples were measured and calculated by a HVS-1000 Vicker’s hardness instrument with a load of 1 kg and a dwell time of 10 s based on ASTM standard E92-82 (American Society for Testing and Materials [21]). Figure 2 shows the hardness measured locations of the tested sample. The tested spots of samples are measured every 30 degrees per circle which has total 11 points but excludes the first and last points. The densities of as-fabricated samples were determined by the Archimedes principle in accordance with ASTM Standard B962-08 [22]. Three tests are preformed and the mean value of density is 7.28 g cm−3. The phase constitutions of worn surface and substrate of the composites were examined by x-ray diffractometry (XRD, D/MAX-RB, RIGAKU Corporation, Japan) with Cu Kα radiation operated at the tension 30 kV and the current of 40 mA. The morphologies and elemental compositions of worn surfaces were characterized by electron probe microanalyzer (EPMA, JXA-8230, JEOL Corporation, Japan) equipped with an energy dispersive spectrometer (EDS). The cross-sections of composites were observed by field emission scanning electron microscope (FESEM, ULTRA-PLUS-43-13, Zeiss Corporation, Germany). The undestroyed cross-sections of composites were obtained by cooling fracture. The method is that sample was incised down to the remaining thickness of 1–2 mm with liquid nitrogen cooling, and then sample was broken by low shearing force under dust-free environment. 3


G Lu et al

Figure 3. The XRD pattern of NMCs fabricated by SPS.

Figure 4. EPMA image showing the microstructrue of NMCs and the EDS results of marked regions.

3. Results and discussion 3.1. Material characterization Ni3Al metal matrix composites containing multi-layer graphene are prepared by spark plasma sintering. The Ni3Al alloy powder has a chemical composition (wt%) of 79.52Ni-8.10Al-5.23Cr-7.02Mo-0.13Zr. The weight of 1.5 wt% multi-layer graphene is chosen to investigate the properties of friction layer. XRD pattern analysis as shown in figure 3 was carried out on the as-prepared material. From the XRD pattern, the peaks of Ni3Al, Cr, Mo and MLG are discerned. It illustrates that the phase compositions of NMCs mainly include Ni3Al alloy matrix phase, as well as a small number of Mo and Cr phases. Although the characteristic peaks of graphene in the XRD pattern are not obvious, it can still be observed the weak diffraction peak at 26.4°. In order to further verify the presence of graphene, it can be determined by EMPA and EDS analysis. Figures 4 and 5 exhibit the EPMA image and the corresponding EDS maps of the surface of NMCs. As shown in figure 4, the gray region over the whole area exhibits a high amount of Ni-based element, thus they are regarded as Ni3Al phase. The chemical composition (wt%) of light gray is 14.26Ni-2.39Cr-68.76Mo-14.59Zr, which shows that Mo-Zr phase is accumulated slightly in the composites. Several black dendritic regions are observed in the composites, which have a chemical composition (wt%) of 69.24Ni-3.16Cr-21.81Al-4.92Mo0.82Zr. EDS spot analysis shows that black dendritic regions exhibit a high amount of Al element over the black areas, demonstrating that they are regarded as Ni3Al phase. It is worth noting that the dendritic Ni3Al phase is liable to form inside the Ni-Cr phase. According to the EDS maps, the added MLG distributes randomly in the alloy matrix. NMCs is predominantly composed of Ni and Al elements, as well as minor amount of Mo, Cr and C elements, which are consistent with the XRD result. 4


G Lu et al

Figure 5. The corresponding EDS maps for the microstructure of NMCs in figure 3.

Figure 6. Subsurface Vicker’s hardness of wear scars as function of sliding time (a), the average wear volumes (b) and the dynamic friction coefficients (c) of NMCs at different loads.

3.2. Tribological properties of NMCs based on hardness of worn scars Figure 6(a) shows the subsurface Vicker’s hardness of wear scars of NMCs as function of sliding time under different applied loads. It shows that the microhardness of NMCs increases with the increase of the sliding time except NMCs at the load condition of 5N. It’s found that the tribological performance of NMCs are heavily affected by hardness[14, 19]. The variation of average friction coefficients and wear volumes with different applied loads as a function of hardness are plotted in figure 6(b). 5


G Lu et al

Figure 7. The average wear volumes (a) and main wear rates (b) of NMCs under different loads from 10N to 20N.

Figure 6(c) shows the dynamic friction coefficients of NMCs under four different applied loads from 5N to 20N. Because of irregular in the hardness and wear volume of applied load 5N as well as it has the highest friction coefficient, three sets of data of 10, 15 and 20N are considered in details. At the initial periods of 10 min, the NMCs at the different applied loads of 10N, 15N and 20N exhibit a relative similar and steady-state friction coefficient of 0.41–0.45, hardness of 565–573 HV and wear volume of 3.9–5.7×104 μm3. With the increase of sliding time, it is interesting to note that NMCs under 15N exhibit the lowest average friction coefficient (0.384) and the stability in wear volume. NMCs under 10N shows the higher friction coefficient and the tendency of wear volume fluctuated slightly. NMCs under 20N at the end of the test exhibits the increase of wear volume. The average friction coefficients under different applied loads of 10N, 15N and 20N are 0.496, 0.384 and 0.463, respectively. Figure 7(a) shows the wear volumes of NMCs tested at four different loads from 10N to 20N. It exhibits that the wear volume increases with the increase of applied load. The greater the load applied, the more the wear volume is. Figure 7(b) shows the mean wear rates under 10N, 15N and 20N from each test are calculated by the final wear volume and formula (2-1). It can be seen that the wear rate of NMCs under 10N has highest value 4.06×10−5 mm3 N−1 m−1. When NMCs under 15N, the wear rate exhibits a low value of 2.48×10−5 mm3 N−1 m−1 and then rapidly increase to a value of 2.875×10−5 mm3 N−1 m−1 when the applied load is 20N. XRD analysis of worn surface under different applied loads is helpful for further understanding and analyzing the effect of microstucture of worn surface and subsurface on wear mechanism, as well as the coupling of friction heat and shear stress produced by heavy applied load. Compared with the XRD results of the initial surface, the diffraction peaks in the XRD of wear scar of NMCs under 15N after the experiment have been broadened (see figure 8). The broadened degree of the diffraction peak also indicates that grain refinement caused by plastic deformation have occurred on the worn surface [23, 24]. Moreover, the worn surface with plastic deformation under heavy applied load in the dry sliding experiment results in the fragmentation and redistribution. The explanation for these results is probably that in the case of the applied load is 10N, the wear mechanism of NMCs is mostly the slight adhesive wear and abrasive wear under cyclic stress and the wear characteristic is higher wear rate and friction coefficient. The sharp reduction of wear volume under applied load of 15N after 15 min of sliding time is attributed to the increase of hardness of wear scar. The formation of sectional oxidation film of worn surface, the grain refinement and surface hardening in the subsurface produced from the fictional heat, cyclic sliding stress and plastic deformation [25, 26], respectively, resulting in the continuous increase of wear scar microhardness of NMCs. Furthermore, this process further strengthens the friction layer and facilitates the low wear rates. The wear volume of NMCs under 20N at the end of test rapidly increases because of spalling and peeling off of wear debris caused by heavy applied load. The above friction and wear results indicate that increased hardness of worn surface affected by applied load during the sliding process could result in the changes in the tribological behaviors. Selected the appropriate load condition at the dry sliding process, a transition to the optimal tribological properties maybe occur during the sliding contact. Meanwhile, microstructural evolution of worn surfaces and in the subsurface of NMCs due to different applied load have a strongly effect on tribological properties. 6


G Lu et al

Figure 8. X-ray diffraction patterns on the worn surface (15N) and substrate of NMCs.

3.3. Structural observation of friction layer As shown in figures 9(a)–(b) and (c)–(d), the deep grooves and severe scratches, as well as a small amount of debris accumulated have been observed on the worn surfaces. However, the worn tracks under heavy applied loads 15N and 20N are relatively smooth and flat (see figures 9(e)–(f) and (g)–(h)), and only a small amount of pits and slight parallel grooves. The relatively darker area are also observed on the worn surfaces (see figures 9(f) and (h)), indicating the presence of oxidation wear. The wear behaviors of NMCs at light applied loads are mostly the adhesive wear and abrasive wear, and the wear characteristics are higher friction coefficient and wear rate. However, at heavy applied loads, NMCs show the oxidative wear and plastic deformation, resulting in the significant increase of wear volume and the decrease of friction coefficient. Moreover, when the applied load is 15N, the worn track is the smoothest surface compared with those under other applied loads. As the applied load continues to increase, the debris and accumulations adhered to the worn surface under heavy applied loads are easily removed along with the sliding process, resulting in the formation of microholes and pits. Therefore, the morphologies of worn surfaces of NMCs are consistent with the results of the friction coefficient and wear volume. Friction and wear behaviors of NMCs should not only present the worn surface of material, but also analyze the wear characteristics of the counterpart ball. Figure 10 exhibits the EMPA micrographs of worn surfaces of the counterpart Si3N4 ceramic balls. Although the microhardness of NMCs (559 HV) is much lower than that of Si3N4 ceramic ball (1530 HV), NMCs still has strong effects on contact surface wear of Si3N4 ceramic ball. The worn surface of ceramic ball under 10N shown in figure 10(a) is very coarse and wear debris with large size and amounts adhered on the worn surface, which are caused mostly through scratching from the softer surface, leading to the severe abrasive wear on surface of the ceramic ball [27]. The worn surface of ceramic ball under 15N exhibits slight plastic deformation shown in figure 10(b), because it can be clearly observed that the worn surfaces of NMCs in figures 9(e), (f) are relatively smooth. The main reason is that the formation of friction layer and oxide films on the worn surface could protect NMCs and counterpart ball from further wear. Figure 11 shows the FE-SEM micrographs of cross-sections of friction layer of NMCs under different loads of 10N(a), 15N(b) and 20N(c). It can be seen that the average thickness of friction layers of NMCs under the load condition of 10N, 15N and 20N are about 4, 7 and 10 μm, respectively. The elements of substrate are more likely to migrate with the increase of applied load; hence, the thickness of friction layer on worn surface forms and increases. With the increase of applied load from 10 to 20N, the contact area between friction pairs becomes larger. On the one hand, The grain size affected by increased load condition also change. It indicates that the contact stress produced by heavy applied load will result in the grain refinement of worn surface, which leads to the increase of microhardness of NMCs, making the microstructures of friction layer of NMCs exhibit more dense and thick structure. These process can further strengthen the worn surface and improve the performance of anti-wear. On the other hand, formation of the local oxides film on the worn surface produced by the coupling of friction heat and shear stress by increased applied load also increase thickness of friction layer. However, the debris and accumulations adhered to the worn surface under applied load of 20N are easily peeling off during the sliding process, resulting in the uneven and deformed interface of friction layer shown in 7


G Lu et al

Figure 9. EPMA images showing the worn surfaces of NMCs tested at the four different applied loads: 5N (a)–(b), 10N (c)–(d), 15N (e)–(f) and 20N (g)–(h).

figure 11(c). MLG particles because of behaviors of diffusion and migration of MLG in the matrix were chosen to add into composites to investigate the properties of friction layer [19, 20]. Figure 12 shows the elemental distribution of C, Ni, O, Al, Cr and Mo of friction layer of cross-section of friction layer of NMCs under 15N detected from line scanning of EDS. The scanning paths is shown in 8


G Lu et al

Figure 10. EMPA micrographs of worn surfaces of counterpart Si3N4 ceramic balls under the different applied loads (a) 10N; (b) 15N.

Figure 11. FE-SEM images showing the cross-sections of the worn samples under applied loads of 10N(a), 15N (b) and 20N (c).

figure 11(b). Elements carbon and nickel have significant changes from friction layer to substrate in figure 12. When the carbon contents rapidly decrease, the nickel content evidently increase. It can be observed that the elemental distribution of cross-section from friction layer to substrate can be divided into three main layers. Meanwhile, the oxygen content detected gradually decreases from worn surface to substrate, which proves that the partial oxides formed on the worn surface after the dry sliding test. Figure 13 shows the FE-SEM micrographs of cross-sections of friction layer of NMCs under 20N. It can be observed that the microstructure of cross-section of friction layer at heavy load conditions can be formed into three main layers. This view was confirmed by Xue et al [28] and Tarasov S et al [6]. The elemental compositions of different layers marked A, B, and C in figure 13(a) were performed by EDS. The results are listed in table 1 and figure 13(b). It is found that the elemental compositions of Ni, Al, Cr, Mo, Zr and O, as well as MLG are distributed variously in three friction layers. The thickness of the friction-affected layer varies with the changing of applied loads. The first layer is the lubricating film formed by plastic deformation and surface hardening, 9


G Lu et al

Figure 12. EDS element line-scanning spectra of cross-section of friction layer of NMCs under 15N.

Figure 13. FE-SEM micrographs of cross-sections of NMCs under 20N (a) and EDS detects from SEM image (b).

Table 1. EDS analysis of element (wt%) in layers marked in figure 10(b). Element

Ni

Al

Cr

Mo

Zr

MLG

O

A B C

33.15 58.25 81.82

9.26 9.61 5.92

6.01 5.83 4.35

11.44 4.72 5.85

1.52 1.92 1.73

32.08 14.41 0.33

8.06 5.26 —

whose thickness is 0–8 μm from the friction surface. The higher load will produce more stress to form the second layer, which is called the transition layer. Under the repeated action of the counterpart ball, the transition layer could mainly support the force of the lubricating film and provide it with excellent mechanical properties. 10


G Lu et al

The influence of load conditions on the friction-affected layer will disappear rapidly in this layer. The third layer is the substrate. Selecting appropriate load conditions, the NMCs not only can form a functional friction layer structure, but also optimize the morphology of contact interface to improve the tribological properties. From the above analysis results, the effects of friction structure on the tribological behavior of NMCs based on behaviors of diffusion and migration of MLG in the matrix can be well proposed. MLG and other elements firstly homogeneously distribute in Ni3Al matrix (see the EDS image of figure 5). During the frictional process, the contact stress and frictional heat produced by different applied loads results in plastic deformation of the worn surface and surface hardening in the subsurface, contributing to increased thickness of friction layer. The special three-layer structures of cross-sections of worn scars are gradually formed at the appropriate load conditions, and every layer has the different function to improve the tribological performance.

4. Conclusion The properties of friction layer formed of Ni3Al matrix self-lubricating composites sliding against Si3N4 ceramic ball under applied loads of 5, 10, 15, 20N have been studied in this paper. Hardness of wear scars, thickness and elemental distribution of friction layer of NMCs are discussed in details. The main conclusions are summarized as follows: (1) Compared with the other load conditions, NMCs exhibits excellent tribological properties at 15N, which leads to the lowest friction coefficient (0.386) and wear rate (2.48×10−5 mm3 N−1 m−1) as well as the smoothest surface of wear track. Because formation of the local oxidation film of worn surface and surface hardening in the subsurface produced from the frictional heat and cyclic sliding stress, respectively, formed a stable and dense friction layer. (2) Hardness of worn surface of NMCs increases with the increase of applied load, this process strengthens the friction layer and facilitates the low wear rate. However, the NMCs under 20N at the end of test exhibits the increase of wear volume because of spalling and peeling off of wear debris caused by the heavy applied load. Selecting appropriate load conditions, at the transition to the optimal tribological properties maybe occur during the sliding contact. (3) The elemental distributions of cross-section of friction layer of NMCs based on behaviors of diffusion and migration of MLG in the matrix show that the frictional structures can be divided into three main layers. The thickness of the friction-affected layer varies with the changing of applied load.

Acknowledgments This work was supported by the Fundamental Research Funds for the Central Universities (2017-YB-019). Authors also wish to thank the Material Research and Test Center of WUT, and X L Nie, S L Zhao, Y M Li and W T Zhu for their assistance with EPMA and FESEM.

ORCID iDs Xiaoliang Shi

https://orcid.org/0000-0003-2370-8039

References [1] Wen S Z and Huang P 2012 Principles of Tribology 4th Edn (Beijing: Tsinghua University Press) [2] Upadhyay R K and Kumaraswamidhas L A 2014 A review on tribology of surfaces and interfaces Advanced Materials Letters 5 486–95 [3] Menezes P L and Kailas S V 2009 Influence of surface texture and roughness parameters on friction and transfer layer formation during sliding of aluminium pin on steel plate Wear 267 1534–49 [4] Gopia V, Sellamuthu R and Arul S 2014 Measurement of hardness, wear rate and coefficient of friction of surface refined Al-Cu alloy Procedia Engineering 97 1355–60 [5] Moshkovic A, Perfilyev V, Bendikov T, Lapsker I, Cohen H and Rapoport L 2010 Structural evolution in copper layers during sliding under different lubricant conditions Acta Materialia 58 4685–92 [6] Tarasov S, Rubtsov V and Kolubaev A 2010 Subsurface shear instability and nanostructuring of metals in sliding Wear 268 59–66 [7] Tarasov S Y, Lychagin D V, Chumaevskii A V, Kolubaev E A and Belyaev S A 2012 Subsurface deformation in copper single crystals during reciprocal sliding Physics of the Solid State 54 2034–8 [8] Ma J P and Yang L F 2016 Measurement methods of friction coefficient for plastic deformation of metals under high strain rate Materials Science Forum 878 127–31 [9] Zhai W, Shi X, Wang M, Xu Z, Yao J, Song S and Wang Y 2014 Grain refinement: a mechanism for graphene nanoplatelets to reduce friction and wear of Ni3Al matrix self-lubricating composites Wear 310 33–40

11


G Lu et al

[10] Xu Z, Chen L, Shi X, Zhang Q, Ibrahi A M M, Zhai W, Yao J and Zhu Q 2015 Formation of friction layers in graphene-reinforced TiAl matrix self-lubricating composites Tribology Transactions 58 668–78 [11] Fricke S, Hager C, Solovyev S, Wangenheim M and Wallaschek J 2018 Influence of surface form deviations on friction in mixed lubrication Tribology International 118 491–9 [12] Moshkovich A, Perfilyev V, Lapsker I and Rapoport L 2014 Friction, wear and plastic deformation of Cu and α/β brass under lubrication conditions Wear 320 34–40 [13] Li J, Lu Y, Zhang H and Xin L 2015 Effect of grain size and hardness on fretting wear behavior of Inconel 600 alloys Tribology International 81 215–22 [14] Zhai W, Shi X, Ibrahim A M M, Xu Z, Yang K and Zhang Q 2017 Effect of hardness ratio on the wear performance and subsurface evolution of Ni3Al matrix composites Tribology Transactions 60 902–12 [15] Liu X B, Liu H Q, Meng X J, Sun C F, Wang M D, Qi L H, Shi G L and Wu S H 2014 Effects of aging treatment on microstructure and tribological properties of nickel-based high-temperature self-lubrication wear resistant composite coatings by laser cladding Materials Chemistry & Physics 143 616–21 [16] Huang Y, Shi X, Yang K, Zou J, Shen Q, Wang Y and Wang Z 2017 Effects of friction layer thickness on the tribological performance of Ni3Al-Ag-MoO3 Journal of Materials Engineering & Performance 26 2313–21 [17] Cheng J, Li F and Zhu S 2017 High temperature tribological properties of a nickel-alloy-based solid-lubricating composite: effect of surface tribo-chemistry, counterpart and mechanical properties Wear 386–387 39–48 [18] Ward D, Gupta A, Saraf S, Zhang C, Sakthivel T S, Barkam S, Agarwal A and Seal S 2016 Functional NiAl-graphene oxide composite as a model coating for aerospace component repair Carbon 105 529–43 [19] Yan Z, Shi X, Huang Y, Deng X, Liu X and Yang K 2018 Tribological performance of Ni3Al matrix self-lubricating composites containing multilayer graphene prepared by additive manufacturing Journal of Materials Engineering & Performance 27 167–75 [20] Nieto A, Bisht A, Lahiri D, Zhang C and Agarwal A 2016 Graphene reinforced metal and ceramic matrix composites: a review Metallurgical Reviews 62 241–302 [21] ASTM, E92-82 e2 2003 Standard test method for Vickers hardness of metallic materials Annual Book of ASTM Standards Vol. 01.10 (Philadelphia, PA: American Society for Testing and Materials) [22] ASTM, B962 2015 Standard test methods for density of compacted or sintered powder metallurgy (PM) products using Archimedes’ principle Annual Book of ASTM Standards Vol. 04.01 (Philadelphia, PA: American Society for Testing and Materials) [23] Rigney D A 2000 Transfer mixing and associated chemical and mechanical processes during the sliding of ductile materials Wear 245 1–9 [24] Li J G, Umemoto M, Todaka Y and Tsuchiy K 2006 Nanocrystalline structure formation in carbon steel introduced by high speed drilling Materials Science and Engineering: A 435-436 383–8 [25] Chen J, Xing X, Wang Y, Zhou Y, Ren X, Yang Y and Yang Q 2015 Effects of vanadium addition on microstructure and tribological performance of bainite hardfacing coatings Journal of Materials Engineering & Performance 24 1157–64 [26] Gao W, Li Z, Wu Z, Li S and He Y 2002 Oxidation behavior of NiAl and FeAl intermetallics under low oxygen partial pressures Intermetallics 10 263–70 [27] Lu X L, Liu X B, Yu P C, Fu G Y, Zhu G X, Wang Y G and Chen Y 2016 Effects of annealing on laser clad Ti2SC/CrS self-lubricating antiwear composite coatings on Ti6Al4V alloy: microstructure and tribology Tribology International 101 356–63 [28] Xue B, Zhu Q, Shi X, Zhai W, Yang K and Huang Y 2016 Microstructure and functional mechanism of friction layer in Ni3Al matrix composites with graphene nanoplatelets Journal of Materials Engineering & Performance 25 4126–33

12