Diamond-like carbon coatings on hard-alloy substrates, including coatings doped with nitrogen about 1.0 μm thick have been obtained using a pulse vacuum-arc method. Three types of coatings have been investigated: a carbon diamond-like coating (C), a carbon coating doped with nitrogen (C : N), and a composite coating based on (C : N + C) layer

Galkina, M. E.

Gerus, J. V.

Kolpakova, A. J.

Kovaleva, M. G.

Poplavskya, A. I.

English

DSpace at Belgorod State University

ISSN 1068-3666, Journal of Friction and Wear, 2018, Vol. 39, No. 4, pp. 345–348. © Allerton Press, Inc., 2018.Original Russian Text © M.G. Kovaleva, A.J. Kolpakov, A.I. Poplavsky, M.E. Galkina, J.V. Gerus, R.A. Lyubushkin, M.V. Mishunin, 2018, published in Trenie i Iznos, 2018,Vol. 39, No. 4, pp. 433–437.Properties of Coatings Based on Carbon and Nitrogen-Doped Carbon Obtained Using a Pulsed Vacuum Arc MethodM. G. Kovalevaa, *, A. J. Kolpakova, A. I. Poplavskya, M. E. Galkinaa, J. V. Gerus,R. A. Lyubushkina, and M. V. MishuninaaBelgorod State National Research University, Belgorod, 308015 Russia*e-mail: Kovaleva@bsu.edu.ruReceived May 25, 2017Abstract—Diamond-like carbon coatings on hard-alloy substrates, including coatings doped with nitrogenabout 1.0 μm thick have been obtained using a pulse vacuum-arc method. Three types of coatings have beeninvestigated: a carbon diamond-like coating (C), a carbon coating doped with nitrogen (C : N), and a com-posite coating based on (C : N + C) layers. The coatings have been annealed in atmospheric air at a tempera-ture of 400°C. The tribological characteristics (wear resistance and friction coefficient change dynamics), theadhesion strength, and the microhardness of coatings in the initial state and after annealing have been stud-ied. The composite coating consisting of C : N + C layers surpasses the constituent coatings in properties,both in the initial state and after annealing at a temperature of 400°C.Keywords: amorphous carbon coatings, pulsed vacuum arc method, annealing, wear resistance, microhard-ness, adhesion, Raman spectraDOI: 10.3103/S1068366618040074INTRODUCTIONThe production of carbon nitride films attractedthe attention of many researchers after the theoreticalprediction of a potential existence of structural state β-C3N4 [1] that should rank over natural diamond inmechanical properties. However, a large number ofexperimental studies have not allowed one to unequiv-ocally confirm this assumption.The authors of [2] reported the results of studiesconcerning carbon nitride superhard and elastic filmsobtained using a vacuum-arc method with plasmaflow filtration. The ions were ionized and acceleratedusing a high-frequency ion source. The nitrogen pres-sure in the vacuum chamber was maintained at a levelof 2 × 10–4 Torr. It was established that, as the energyof nitrogen ions increased to 100 eV, the microhard-ness, the modulus of elasticity, and the elastic recoveryexhibited an increase to 47 GPa, 400 GPa, and 87.5%,respectively. Any further increase in the energy ofnitrogen ions resulted in a deterioration of these prop-erties, which was attributed by the authors to anincrease in the size of graphite clusters.The pulse vacuum arc technique for obtaining dia-mond-like carbon coatings [3] has a number of advan-tages over other methods. The authors of [4] reportedthe results of complex studies concerning the structureand properties of nitrogen-doped amorphous carboncoatings (a-C:N) obtained in vacuum using a pulsedcarbon plasma flow. It was established that the nitro-gen doping of a carbon coating leads to an increase inelectrical conductivity, to a decrease in internalstresses, to a decrease in density, hardness, and elasticmodulus, and to a change in the structure, surfacemorphology, and tribological characteristics as com-pared to an undoped coating (ta-C). It was shown thatthe a-C:N coatings are significantly inferior to ta-Ccoatings in the values of hardness and modulus of elas-ticity, but they are more elastic and are not subjectedto brittle fracture in the form of cracks and chips.The effect of annealing in vacuum exerted on thetribological characteristics of nanoscale carbon coat-ings doped with nitrogen was studied by the authors of[5]. It was established that the annealing of these coat-ings in vacuum at a temperature of 600°C resulted in athreefold increase in their wear resistance.The results of the studies presented in [6] are ofparticular interest, since they indirectly confirm theexistence of a theoretically predicted new species ofcrystalline carbon nitride β-C3N4 [1]. Crystalline car-bon nitride was obtained via magnetron sputteringwith additional ion irradiation and subsequent anneal-ing in a nitrogen atmosphere. The microstructure ofthe coating was investigated using X-ray diffraction(XRD) and transmission electron microscopy (TEM).The film was shown to contain a very dense and uni-form distribution of crystalline grains, the crystal lat-tice parameters and the type of crystal lattice being ingood agreement with the parameters of theoreticallypredicted carbon nitride crystalline species β-C3N4.345346 KOVALEVA et al.Fig. 1. Tribological characteristics of carbon coatingsbefore and after annealing: (1) C400; (2) C:N400;(3) C:N + C; (4) (C:N + C)400.0.10.30.20.40 500 1500 2500200010002 1 3 4Coefficient of frictionRubbing path, mThe X-ray photoelectron spectroscopy (XPS) alsoconfirmed the presence of sp3-hybridized C–N bondsin the film. The concentration of particles of crystal-line carbon nitride in the film is 43.91%, which ishigher than that obtained in previous works. Theinterest in this work is also caused by the fact that wepublished a paper [7] in which we described a newphase of crystalline carbon formed upon annealing invacuum at a temperature of 600°C in an amorphouscarbon matrix obtained using a pulsed vacuum arctechnique. Thus, the same approach to the modifica-tion of the structure of carbon coatings can be traced.It is of interest to obtain a combined coating basedon a-C:N and ta-C layers, followed by annealing inatmospheric air, as well as to study the properties ofthis coating in the initial state and after the action of anelevated temperature.This work was aimed at obtaining, studying, andcomparatively analyzing the tribological characteris-tics, microhardness, and adhesion strength of carboncoatings (C, C:N, and combined ones on the basis ofC:N + C layers) before and after annealing at 400°C.EXPERIMENTALThe carbon coatings were obtained using aUVNIPA-1-011 experimental facility modernized inthe part of power supply units and equipped with anion source, a vacuum arc source of a metal plasmawith a plasma flow separation system, and a pulse car-bon plasma source. The samples represented disksmade of solid alloy (WC) based on tungsten carbideand cobalt with a diameter of 20 mm and a thicknessof 3 mm. The samples were polished using diamondpastes; then they underwent a cleaning operation in anultrasonic bath and drying in an oven at a temperatureof 100°C. The vacuum chamber was pumped to a pres-sure no higher than 5 × 10–5 mmHg.Further, ion purification was carried out usingaccelerated argon ions at a pressure of 5 × 10–3 mmHg,JOURNAa discharge voltage of 2.0 kV, and a discharge currentof 100 mA for 10 min. After that, a purification by tita-nium ions and an application of a titanium sublayerwas performed. Next, a carbon diamond-like coatingwas deposited using a pulsed vacuum arc method inthe following modes: charge storage voltage 300 V,charge storage capacitance 2000 μF, pulse repetitionrate 5 Hz. The coating thickness was 1.0 μm. A carboncoating doped with nitrogen was produced via nitro-gen injection into an ion source for ionization at apressure of 5 × 10–3 mmHg.The following three types of coatings were investi-gated: a carbon diamond-like coating (C), a nitrogen-doped carbon coating (C:N), and a layer-based com-posite coating (C:N + C). The coatings were annealedin an air atmosphere at a temperature of 400°C for10 min. For annealing, a Nabertherm LT5/12/B170muffle furnace was used. The tribological characteris-tics (the wear resistance and the changing dynamics ofthe friction coefficient), the adhesion strength, andthe microhardness of coatings in the initial state andafter annealing were studied. The wear resistance ofthe coatings was tested using a laboratory benchaccording to a scheme “disk–flat coated sample”under conditions of dry friction until the coating wascompletely worn, which was fixed by an abruptincrease in the coefficient of friction.The counterbody represented a disk with a diame-ter of 10.0 mm made of of the corrosion-resistant steel(Fe–0.12C–0.90Mn–0.025P–0.01S–16Cr–0.20Cu,all in wt %). The load on the disk was 50 g. The inves-tigations were carried out at a relative slip velocity of0.5 m/s. The hardness of the coatings was studiedusing a technique of “instrumental indentation” (Rus-sian State Standard ISO 14577–1:2002) using a Shi-madzu DUH-211S ultra microhardness meter. Theindentation was carried out at an indentation load of100 and 200 mN. To determine the adhesion of thecoating to the substrate, a sclerometric (scratching)test was used. In this case, a Revetest scratch tester(CSM Instruments) was used to determine the adhe-sion/cohesion strength and scratch resistance, as wellas to determine the fracture mechanism.The moment of the adhesive or cohesive destruc-tion of the coatings was registered after the testingvisually by means of an optical microscope equippedwith a digital camera, as well as according to change inthe acoustic emission and the coefficient of friction.As a result of the tests, the minimum (critical) load Lcwhich led to the coating destruction was determined.To study the structural changes caused by the action oftemperature, Raman spectroscopy was applied using aLabRAM HR Evolution Raman spectrometer (laserwavelength 532 nm, power 50 mW).RESULTS AND DISCUSSIONFigure 1 shows the results of studies concerning thetribological characteristics of carbon coatings beforeand after annealing until their total wear, which isL OF FRICTION AND WEAR  Vol. 39  No. 4  2018PROPERTIES OF COATINGS BASED ON CARBON AND NITROGEN-DOPED CARBON 347Fig. 2. Instrumental microhardness of coatings C, C:N,and C:N + C in the initial state and after annealing at atemperature of 400°C at different indentation loads:(1) 100 mN; (2) 200 mN.10 00020 00030 00040 00050 00060 0000C WCC400C:N C:N + С(C:N + C)400C:N400Instrumental microhardness, N/mm21 2Fig. 3. Raman spectra of carbon coatings (1) and carboncoatings doped with nitrogen (2) after annealing at a tem-perature of 400°C.200150300250400350450501005000 1500 2000 2500100012CountsRaman shift, cm–1indicated by an abrupt increase in the coefficient offriction. The C:N + C coating is the most wear-resis-tant one, both in the initial state and after annealing ata temperature of 400°C.Figure 2 shows the results of measuring the instru-mental microhardness of C, C:N, and C:N + C coat-ings in the initial state and after annealing at a tem-perature of 400°C. It should be noted that the com-posite coatings based on carbon and carbon layersdoped with nitrogen (C:N + C) exhibit the greatestmicrohardness. An important result is the effect ofincreasing microhardness exerted by C and C:N + Ccoatings after annealing at a temperature of 400°C.A similar result has been obtained for the wear resis-tance of the same coatings.The results of measuring the adhesion characteris-tics of carbon coatings are summarized in Table 1.Analyzing the results given in Table 1, we shouldnote that a C:N + C coating has the greatest adhesivestrength in the initial state, whereas after annealing aJOURNAL OF FRICTION AND WEAR  Vol. 39  No. 4 Table 1. Adhesion characteristics determined for carboncoatingsNo. CoatingCritical load, Nin the initial stateafter annealing1 С 12 242 C:N 18 283 C:N + C 24 16C:N coating is the most adhesive one. In this case, theannealing leads to an increase in the adhesion strengthof C and C:N coatings, but to a decrease in this valuefor the C:N + C coating.Figure 3 shows Raman spectra of carbon coatings(C) and carbon coatings doped with nitrogen (C:N)after annealing at a temperature of 400°C.It should be noted that the spectrum of the carboncoating in the initial state does not differ from thatshown in Fig. 3. The spectrum of the carbon coatingdoped with nitrogen in the initial state is characterizedby a higher intensity of peaks.The results obtained can be considered as a confir-mation of the conclusions made by the authors of [7]that annealing leads to an improvement in the wearresistance of coatings as a result of structural changesassociated with the phenomenon of local crystalliza-tion. This effect was established using a technique ofhigh-resolution transmission electron microscopy(HRTEM).CONCLUSIONSIt is established that the characteristics of a com-bined coating consisting of C:N + C layers ranks overthe characteristics of the composing coatings, both inthe initial state and after annealing at a temperature of400°C. At the same time, the annealing does notworsen the properties of this coating, but on the con-trary, it causes their properties to improve. This effectcan be explained by the structural changes associatedwith local crystallization in the matrix of amorphouscarbon. In addition, the results obtained have anapplied value, since they make it possible to increase 2018348 KOVALEVA et al.the tribological characteristics of diamond-like car-bon coatings used in friction assemblies.ACKNOWLEDGMENTSThis work was carried out within the scope of theproject of the Russian Foundation for Basic Researchno. 15-48-03072 “Formation Patterns and Propertiesof Amorphous Carbon Coatings with W, N, AgAdmixtures Produced by Pulsed Vacuum ArcMethod” using the equipment of the Joint ResearchCenter of Belgorod State National Research Univer-sity “Technology and Materials”.REFERENCES1. Liu, Y. and Cohen, M.L., Prediction of new low com-pressibility solids, Science, 1989, vol. 245, no. 4920,pp. 841–842.2. Cheng, Y.H., Tay, B.K., Lau, S.P., Qiao, X.L., Chen, J.G.,Sun, Z.H., and Xie, C.S., Micromechanical propertiesof carbon nitride films deposited by radio-frequency-assisted filtered cathodic vacuum arc, Appl. Phys. A:Mater. Sci. Process., 2002, vol. 75, pp. 375–380.3. Maslov, A.I., Dmitriev, G.K., and Chistyakov, Yu.D.,Pulsed source of carbon plasma for technological pur-poses, Prib. Tekh. Eksp., 1985, no. 3, pp. 146–149.4. Poplavsky, A.I., Kolpakov, A.Ya., Galkina, M.E.,Goncharov, I.Yu., Lyubushkin, R.A., and Gerus, J.V.,Properties of nitrogen-doped amorphous carbon coat-ings obtained by pulsed vacuum arc method, Izv. Vyssh.Uchebn. Zaved., Khim. Khim. Tekhnol., 2016, vol. 59,no. 9, pp. 68–73.5. Poplavsky, A.I., Kolpakov, A.Ya., Kovaleva, M.G.,Galkina, M.E., and Bondareva, E.N., Effect of anneal-ing in vacuum on electrical conductivity and tribotech-nical characteristics of nanocarbon nitrogen-contain-ing coatings, Nauch. Ved. Belgorod. Gos. Univ., Ser.:Matem. Fiz., 2013, no. 26 (169), pp. 176–180.6. Liu, D.G., Bai, W.Q., Pan, Y.J., and Tu, J.P., Crystal-line carbon nitride film synthesized by ion beamassisted magnetron sputtering and thermal annealing innitrogen gas, Diamond Relat. Mater., 2015, vol. 55,pp. 102–107.7. Kolpakov, A.Ya., Poplavsky, A.I., Galkina, M.E.,Manokhin, S.S., and Gerus, J.V., The local crystalliza-tion in nanoscale diamond-like carbon films duringannealing, Appl. Phys. Lett., 2014, vol. 105, art. ID233110.Translated by O. PolyakovJOURNAL OF FRICTION AND WEAR  Vol. 39  No. 4  2018

Properties of coatings based on carbon and nitrogen-doped carbon obtained using a pulsed vacuum arc method

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Properties of coatings based on carbon and nitrogen-doped carbon obtained using a pulsed vacuum arc method

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