Mo2N nano-multilayer films synthesized by multi-cathodic arc ion plating system

    Properties of CrN/Mo 2 N nano-multilayer films synthesized by multi-cathodic arc ion plating system B. Han, V.O. Pelenovich, M.I. Yousaf, S.J. Yan, W. Wang, S.Y. Zhou, B. Yang, Z.W. Ai, C.S. Liu, D.J. Fu PII: DOI: Reference:

S0040-6090(16)30620-4 doi:10.1016/j.tsf.2016.10.074 TSF 35607

To appear in:

Thin Solid Films

Received date: Revised date: Accepted date:

30 December 2015 25 August 2016 12 October 2016

Please cite this article as: B. Han, V.O. Pelenovich, M.I. Yousaf, S.J. Yan, W. Wang, S.Y. Zhou, B. Yang, Z.W. Ai, C.S. Liu, D.J. Fu, Properties of CrN/Mo2 N nano-multilayer films synthesized by multi-cathodic arc ion plating system, Thin Solid Films (2016), doi:10.1016/j.tsf.2016.10.074

This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.

ACCEPTED MANUSCRIPT Properties of CrN/Mo2N nano-multilayer films synthesized by multicathodic arc ion plating system

PT

HAN B.1, PELENOVICH V. O.1,3, YOUSAF M. I.1, YAN S. J.1, WANG W.1, ZHOU

RI

S.Y.1, YANG B.2, AI Z. W.1, LIU C. S.1, FU D. J.1,* 1

Key Laboratory of Artificial Nano- and Micro-Materials of Ministry of Education, School of Physics and

SC

Technology, Wuhan University, 430072 Wuhan, China 2

NU

School of Power & Mechanical Engineering, Wuhan University, 430072 Wuhan, China

3

Institute of Ion-Plasma and Laser Technologies, Academy of Sciences of Uzbekistan, 700135 Tashkent, Uzbekistan

MA

*

Corresponding Author: D.J. Fu; Tel/Fax: +86-27-6875-3587; e-mail: [email protected];

D

Abstract: CrN/Mo2N films were deposited by multi-cathodic arc ion plating on Si (100),

TE

304 stainless steel and cemented carbide substrates with various bilayer periods (10–105

AC CE P

nm). X-ray diffraction analysis revealed a face-centered-cubic structure of CrN and Mo2N sublayers. Rutherford backscattering spectrometry (RBS) was used to probe the elemental composition and their depth profiling. The multilayer structures exhibited characteristic oscillating RBS spectra. The nanohardness slightly increased at larger bilayer periods and the highest value of 29 GPa was obtained at the bilayer period of 105 nm. A correlation was realized among compressive residual stress, critical load, and nanohardness. The highest critical load Lc2 of 65-70 N was found for the coatings on cemented carbide substrates with the minimal bilayer period of 12 nm. The coefficients of friction and wear rates of the coatings were in the range of 0.29-0.35 and (6-8)10-7 mm3/N·m, respectively. Keywords: CrN/Mo2N; nano-multilayer; cathodic arc ion plating; nanohardness; wear rate PACS: 52.77.Dq; 81.15.-z 1

ACCEPTED MANUSCRIPT

1.

Introduction

PT

Transition metal nitrides such as TiN, CrN, and TiAlN are widely used as protective

RI

coatings for cutting tools and mechanical parts owing to their high hardness and wear resistance [1-5]. Particularly CrN coatings exhibit excellent resistance against oxidation,

SC

wear, and corrosion [6,7]. Nevertheless, CrN has rather high coefficient of friction (COF)

NU

(0.4-0.8) in air [5,8,9]. Another protective nitride film, MoN in its hexagonal δ-MoN phase has a very useful property of self-lubrication over a wide temperature range, which

MA

leads to low COF (~0.18) and low wear rate [10-12]. MoN as a monolayer may offer unique applications not only in machining but also in sliding and bearing. Koshy et. al.

TE

D

[13] have demonstrated that the excellent tribological properties result from the formation of lubricious oxides, such as MoO3. However, the mechanical properties of these

AC CE P

materials which are in the form of single-component coating cannot fully satisfy the demands of machining of various hard or high performance materials. It has been proved that the multilayer coatings possess higher hardness and toughness when compared with the monolayers [14,15]. The significant increase in the hardness of the nano-multilayer films is reported to be associated with epitaxial stabilization effect (template effect) [16]; the sublayers tend to form coherent interface to minimize the interfacial energy, i.e. one of the sublayers reproduces the crystal structure of the other sublayer owing to its unfavorable thermodynamic state. High resolution transmission electron microscopy (HRTEM) is useful to observe this phenomenon of nano-crystallites composed of a few sublayers..

2

ACCEPTED MANUSCRIPT Fabrication of CrN/Mo2N multilayered structures is one of the feasible ways to decrease the COF of bearing coatings, for example from 0.6-0.8 to 0.3-0.4 for CrN,

PT

which can result in a significant improvement in tool-life. Such CrN/Mo2N multilayered

RI

structures were grown by sputter deposition in an unbalanced-magnetron system [13,17]. In these studies reduced COF at the room temperature (0.4 against sapphire ball) and

SC

presence of MoO3 lubricating phase were detected. The hardness was in the range of 23–

NU

26 GPa and was dependent on bilayer periods. A recent study, devoted to Mo2N/CrN multilayer coatings deposited by cathodic arc evaporation (CAE) [18] showed hardness

MA

of 26 GPa and lower multistructure COF in comparison with single layers; the coatings also showed good critical force to the substrate, the Lc2 values (spallation at the side of

TE

D

the scratch groove) were up to 59 ± 4 N, which were higher than the Mo2N coating (40 N) and lower than CrN coating (95 N). The residual stress (RS) was studied for the

AC CE P

Mo2N/CrN multilayer coatings prepared by CAE [18] and RF magnetron sputtering (MS) [19], the studies revealed compressive stress of –2 and tensile stress of 0.15 GPa, respectively. The compressive stress in the coating, which is favorable to promote the hardness and adhesion, can be caused by high-energy ion bombardment during the deposition process [18].

The present work reports a thorough study of microstructure, mechanical, and tribological properties of nano-multilayered CrN/Mo2N films prepared by cathodic arc ion plating (CAIP) employing Cr and Mo as metal targets. An enhanced ion bombardment used in CAIP in comparison with MS and CAE is expected to increase adhesion, residual stress, and nanohardness of the films. The effects of substrate rotation speed (SRS) on the multilayer structure and hardness as well as influence of Mo nitride 3

ACCEPTED MANUSCRIPT on tribological performance of the CrN/Mo2N multilayers are also studied. Rutherford backscattering spectroscopy (RBS) is used to study the depth profiling and chemical

2.

RI

PT

composition of nano-multilayer structure.

Experimental details

SC

CrN/Mo2N multilayered coatings were deposited on Si (100), 304 stainless steel,

NU

and YT15 cemented carbide (WC-TiC-Co) substrates by a home-made multi-cathodic arc plasma deposition system, described elsewhere [20], using Cr and Mo metal targets of

MA

purity more than 99.95%. To deposit multilayered films turn-table rotation was used. Before deposition the chamber was evacuated to the base pressure of 10-3 Pa. The

D

substrates were cleaned by standard technique using ultrasonic degreasing and were

TE

exposed to bombardment by Cr+ ions at – 800 V bias voltage for 10 min for further

AC CE P

removal of contaminants from the surface of the substrates. Next the deposition of CrN interlayers was conducted for up to 5 min in N2 atmosphere at 2 Pa and at a bias voltage of – 200 V. Finally, the deposition of CrN/Mo2N films was carried out under the same conditions for 35 min (Cr and Mo target currents were set to 65 A and 75 A, respectively, substrate temperature was 380oC). The SRS was varied from 1 rpm to 6 rpm. Monolayer CrN and MoN coatings were prepared and used as reference samples. The crystal structure of the prepared films was characterized by X-ray diffraction (XRD) technique using D8 Advance diffractometer with a Cu Kα radiation and HRTEM 2010 FEF (UHR) operated at 200 kV. The thickness and modulation period of the multilayers were evaluated by cross-section scanning electron microscopy (SEM) using a Sirion FEG operated at 20 kV and also by transmission electron microscope (TEM) 4

ACCEPTED MANUSCRIPT JEOL 2010(HT). An atomic force microscope (AFM) Shimadzu SPM-9500J3 operated in the tapping mode was used to analyze the surface topography of the films within a

PT

measuring area of 5×5 μm2. EDAX genesis 7000 energy dispersive spectroscopy (EDS) equipment was used to determine the chemical composition of the coatings. To study the

RI

composition and structure of the coatings RBS technique was used with a 1.52 MeV Li2+

SC

beam. The scattered incident ions were detected by a silicon surface barrier detector at a

NU

backscattering angle of 170o. SIMNRA software was used to fit the RBS spectra. The nanohardness was measured by nanoindentation (Agilent G200) operated in continuous

MA

stiffness measurement mode. A three-sided Berkovich-shaped indenter with 60 nm tip radius was used and the maximum indentation depth was 500 nm. The load displacement

D

data were statistically averaged over five measurements for each sample. The RS was

TE

measured by the sin2ψ technique on a D8 Advance diffractometer. The scratch test was

AC CE P

conducted on an HH-3000 tester by increasing the normal load continuously from 0 to 100 N at a loading rate of 100 N/min and moving speed of 5 mm/min. The critical load Lc1 (first cracking) was evaluated by acoustic emission signals, and an optical microscope was used to evaluate the critical load Lc2, both values were averaged over 4-5 measurements per sample. The COF and wear tests were performed at ambient temperature, pressure and relative humidity of 60%, on MS-T3000 ball-on-disk tester equipped with a 3 mm Si3N4 ball working under 5 N load. The sliding speed and time was 2 cm/s and 60 min. Wear tracks were also examined by SEM and EDS techniques. Normalized wear rate was evaluated from cross-sectional profiles of wear scar by using Taylor Hobson FISS2-S4C stylus profilometer.

5

ACCEPTED MANUSCRIPT 3. Results and discussion Fig. 1 shows XRD patterns of the multilayer coatings deposited at different SRS and

PT

monolayers on 304 stainless steel substrates. CrN single layer exhibits face-centered-

RI

cubic phase (PDF#77-0047), whereas MoN single layer demonstrates hexagonal δ-MoN structure (PDF#89-5024). The patterns of the multilayered coatings reveal the presence of

SC

face-centered-cubic CrN with the preferable (311) orientation. A shift towards lower

NU

angles is observed in the patterns of the multilayered coatings when compared with the single-component layer of CrN, which indicates an expansion of the CrN crystal cell. The

MA

crystal cell parameter a obtained from the cell refinement of the corresponding XRD patterns of CrN multistructure and single layer is 4.21 and 4.17 Å, respectively, suggests

TE

D

that the MoN sublayers possess would have compressive stress. The (311) peak of the coatings deposited at low rpm exhibits a shoulder at higher angle side suggesting the

AC CE P

presence of a second phase with the same crystal structure, this phase was identified as cubic Mo2N (PDF#25-1366), with the same preferable orientation along (311). The size of grain estimated by Debye-Scherrer formula using the two peak broadening is about 7-8 nm. From the above results it can be inferred that the MoN tends to form cubic Mo2N with the crystal cell parameters which are close to CrN cubic phase in the multilayered structure, which are required to minimize the interfacial energy between the sublayers. This can be also testified by the increased crystal cell parameters of CrN up to that of Mo2N as a consequence of the observed shift in the CrN patterns to lower angles. Moreover, the (311) peak loses its asymmetry at higher rpm, which can be explained by the fact that at the smaller bilayer period the requirement of interfacial energy

6

ACCEPTED MANUSCRIPT minimization results in the formation of the sublayer phases with closer crystal cell parameters.

PT

Fig. 2 (a-b) shows surface and cross-sectional SEM images of the sample prepared

RI

at 2 rpm on cemented carbide substrate. The surface morphology represents the existence of microparticles and pit holes originated from the removed particles. The thickness of all

SC

the samples under study measured from SEM images is about 5 μm (Table 1). The

NU

multistructure of the samples can easily be distinguished using TEM images. Fig. 3 depicts the TEM image of the sample prepared at 6 rpm, where the bright fringes are

MA

identified as CrN and the dark ones as MoN. It can be seen from the TEM image that the bilayer consists of sublayers with almost identical thicknesses. The selected-area electron

TE

D

diffraction (SAED) pattern (inset of Fig. 3) shows well defined rings suggesting that the selected area mostly contains polycrystalline structure, and the pattern is in good

AC CE P

agreement with the (111), (200), (220), and (311) peaks observed in XRD patterns. The bilayer period as a function of SRS estimated from SEM and TEM images are presented in Table 1. The bilayer period decreases from 105 nm to 12 nm with increasing rotation speed from 1 rpm to 6 rpm. Figs. 4a and 4b show HRTEM images of the 6 rpm sample. Both the figures demonstrate superlattice effect of the film and Fig. 4a reveals both crystal and amorphous components of the sample, and a nanoparticle of 25 nm in size contains five sublayers (enclosed in oval). The measured lattice spacing of CrN and Mo2N sublayers corresponding to (111) planes are about 0.245 nm as shown in the inset. Fig. 4b shows less amorphous matrix and more superlattice phase growth. The AFM images of 2 and 5 rpm films are presented in Fig. 5, which represents the roughness and

7

ACCEPTED MANUSCRIPT surface morphology. All the multilayered structures demonstrate rather smooth surface morphology with root mean square roughness less than 10 nm (Table 1).

PT

Atomic concentration of the elements that present in the coatings measured by EDS

RI

technique is given in Table 1. The data were collected from different areas of the samples and averaged over 3-5 measurements. There is no any observed influence of SRS on

SC

chemical composition of the coatings. The overall averaged ratio of the elements

NU

Mo:Cr:N is 4:5:6. The concentration of nitrogen slightly exceeds the stoichiometric value of 40 at%, which may be an evidence for the presence of amorphous MoN phase with the

MA

Mo:N ratio less than 2:1. The EDS analysis of MoN single layer shows the Mo:N ratio of about 1:1.2, i.e., there is a deficiency of Mo in δ-MoN phase, whereas the CrN single

TE

D

layer demonstrates a deficiency of nitrogen. The measured concentration ratio Mo:Cr is mainly controlled by the thickness ratio of the Mo2N and CrN layers, i.e., by the rate of

AC CE P

deposition of each sublayer.

To determine the element profiling and bilayer period of the coatings, RBS analysis was carried out. The RBS spectra of the films grown by different SRS are presented in Fig. 6. Characteristic RBS spectra of multilayered structure are observed, such oscillating spectra suggest low interlayer and surface roughness, and up to 15 layers are observable. Using known molar masses and volume densities of each material 9.46 g/cm3 for Mo2N and 5.9 g/cm3 for CrN [21], combining them with the thickness of each sublayer from RBS simulation data, we can calculate the bilayer period of the coating. However, the calculated bilayer period of the Mo2N sublayers is in 1.5 times larger than that obtained from SEM/TEM measurements. This can be explained in light of the presence of other phase structures of Mo nitride. According to HRTEM images, amorphous MoN phase 8

ACCEPTED MANUSCRIPT may also present in the coatings. In order to quantify RBS data compared with SEM/TEM results, a ratio of Mo2N:MoN = 2:1 is preferred, where Mo2N and MoN

PT

correspond to the crystal and amorphous phases in the sublayer, respectively (Table 1).

RI

Simultaneously, the calculated thickness ratio of CrN sublayer over Mo2N is close to 1.5:1, which is in agreement with the HRTEM data. The RBS also gives information of

SC

the top layer of the films. From Fig. 6 one can derive the energies by which the

NU

molybdenum is detected, they are 1104 keV, 1140 keV, 1039 keV and 1085 keV for films prepared at rotation speeds of 2, 3, 4, and 6 rpm, respectively. Hence, it can be

MA

concluded that 3 rpm sample has a MoN top layer, assigned by the smallest peak. This indicates that the deposition process was stopped during the MoN sublayer growth. For

different thicknesses.

TE

D

the other samples, the reduced energies suggest the presence of CrN top layers with

AC CE P

The data of nanohardness of the CrN/Mo2N multistructures with different SRS and of the monolayers are listed in Table 2. Both the monolayer and multistructured samples were prepared under the same conditions. The nanohardness of the CrN/Mo2N multistructures is slightly higher than those of the MoN and CrN single layers, which are 27 and 23 GPa, respectively. This effect is well known in literature and has been observed in some multistructured films possessing MoN and CrN layers such as AlTiN/MoN [20] and AlTiN/CrN [22]. The nanohardness of the multistructures has a maximum at 29 GPa for the sample grown at SRS of 1 rpm. A decrease of the nanohardness is observed along with decrease of the bilayer thickness, similar to the AlTiN/MoN system [20].

9

ACCEPTED MANUSCRIPT The RS measured by the sin2ψ technique using (311) reflection peak is presented in Table 2. All stresses are compressive in the range of -4.6 ~ -1.8 GPa, which are twice

PT

higher those found in Ref. 18. Such higher values can be explained by a more effective

RI

ion bombardment, provided by the higher negative substrate bias voltage, which would create more point defects during the deposition process, resulting in increased

SC

compressive RS [23]. The RS decreases with the bilayer period, such dependence

NU

correlates with the above-mentioned dependence of nanohardness on bilayer period, indicating reduction of the hardness during the stress relief [13]. The decrease can be

MA

explained by an influence of higher bias voltage used in CAIP, which is favorable to form diffused and intermixed regions between sublayers. Indeed, when the bilayer period

TE

D

decreases, such regions play a more prominent role in reducing the sharpness of the interface. Similar results are reported by some earlier researches [24,25]. From the

AC CE P

HRTEM image of the 6 rpm sample, the diffused regions are clearly observed (Fig. 4a), in the form of mixed regions of thickness ~1-2 nm between CrN and Mo2N sublayers. Furthermore from the XRD patterns (Fig. 1) it is seen that the (311) peak at higher SRS becomes singlet, suggesting a trend to form single phase, which also can reduce the internal stress initially caused by mismatch of CrN and Mo2N crystal structures. To estimate the adhesion of the coatings critical load measurements were carried out. The coatings deposited on 304 steel substrate show Lc1 (first cracking) of 10-15 N for 1-2 rpm samples and 25-35 N for 3-6 rpm samples, this result is comparable with that of previous study [18]. Lower Lc1 of the first group of the samples can be explained by higher RS in the coatings. It is well known that brittleness of hard films deposited on a soft substrate (stainless steel, hardness of 200 HV) results in considerable decrease of the 10

ACCEPTED MANUSCRIPT critical load. Indeed, the measured values of Lc1 and Lc2 for the films deposited on cemented carbide (1600 HV) show much better adhesion, up to 65-70 N (Table 2) with

PT

similar dependence of Lc2 on the RS and adhesion failure. Such rather high critical load

RI

can be caused by enhanced ion bombardment used in CAIP, high energetic ions of the coating material as well as Ar ions colliding with the substrate surface can promote

SC

intensive mixing of the substrate and coating materials, which results in inter-diffusion

NU

and enhanced roughness at the interface, and as a consequence, good adhesion. The optical microscopy revealed that the first cracking detected by acoustic emission

MA

corresponds to the semicircular cracks in the scratch track perpendicular to the indenter movement as well as small detachment of the coating at the side of the scratch groove,

(delamination) failure.

TE

D

i.e., Lc1 ≈ Lc2, which demonstrates high resistance against spalling and adhesion

AC CE P

The COFs of the coatings sliding against Si3N4 ball are listed in Table 2. The COFs of all the multistructures are in the range of 0.29-0.34 and slightly increase with the sliding distance (by 10 % at sliding distance of 100 m). The single layer of MoN possesses a similar COF of 0.33, whereas CrN single layer has a much higher COF (~0.53), both measured values are in agreement with the previous literature data for δMoN [11] and CrN [8,26]. The reduction of the COFs can be a result of the appearance of molybdenum oxides (Magnelli phases), which can be formed at tribochemical surface oxidation during the dry sliding due to shearing of micro-asperities and deformation [13,27]. The reduction of the COFs of multistructures results in decrease of the wear rates, which were obtained from the wear scar profiles and presented in Table 2. The wear rate of the single-component layer CrN is 13.610-7 mm3/N·m. The wear rate of CrN/Mo2N 11

ACCEPTED MANUSCRIPT multistructures is decreased and becomes comparable with that of MoN monolayer. The result shows good correlation between the wear rates and COFs. However, COFs as well

PT

as wear rates demonstrate independence of the bilayer period. It can be related to ratio

RI

between bilayer period and wear scar depth. If the depth of the scar is much larger than the bilayer period, the Si3N4 ball, having finite radius, contacts many sublayers of both

SC

kinds in the scar, that results in averaging of COFs of CrN and MoN2 sublayers and

NU

independence of the bilayer period. In our experiment, the scar depth is in the range of

MA

300 – 500 nm, whereas the bilayer periods are in the range of 10-100 nm. The wear tracks produced during ball-on-disc test measured by SEM and EDS are

D

shown in Figs. 7a and 7b for the 3 and 6 rpm samples. All the multilayered samples and

TE

MoN single layer were not completely worn off and show smooth surface without any chipping and delamination of the coatings, except small holes, which were formed after

AC CE P

removing of metal droplets (Figs. 7c and 7d). The EDS analysis also does not show any difference between the coating composition of inside and outside wear tracks. 4. Conclusion

CrN/Mo2N multilayer films were synthesized by using a home-made cathodic arc ion plating system using Cr and Mo metal targets in nitrogen atmosphere at different SRS (1-6 rpm). XRD study of single-component layers of Mo- and Cr-nitrides showed formation of hexagonal δ-MoN and face-centered-cubic CrN phases, respectively, whereas in multistructures the growth of cubic Mo2N was observed and the crystal cell parameters become close to those of CrN. The bilayer period of the films was in the range of 12-110 nm depending on SRS. The crystal size of the both phases in the coatings was about 8 nm. The RBS analysis showed characteristic oscillating spectra for 12

ACCEPTED MANUSCRIPT multistructure, suggesting a low interlayer roughness. Fitting of the RBS spectra revealed the presence of possible amorphous MoN phase in Mo2N sublayers. Compressive RS (-

PT

4.6 ~ -1.8 GPa), critical load (29~70 N), nanohardness (29~23 GPa), and SRS are

RI

correlated. The nanohardness showed a slight decrease at lower bilayer periods. Whereas the highest critical load Lc2 of 65~70 N was found for the films deposited at higher SRS

SC

on cemented carbide substrates. Enhanced values of RS and critical load are explained by

NU

effective ion bombardment during the deposition process. The COFs of the multilayered coatings in the ball-on-disc experiment demonstrated a low value 0.33 in comparison

MA

with 0.53 of the CrN single layer. The wear rates of multilayers were in the range of 6-

TE

and delamination of the films.

D

810-7 mm3/N·m, and there is no change in the composition in the wear track, chipping,

Acknowledgment: This work was supported by National Natural Science

AC CE P

Foundation of China under grants 11375135 and 11405117, the International Science & Technology Cooperation Program of China under 2015DFR00720, and the Suzhou Scientific Development Project ZXG201448.

13

ACCEPTED MANUSCRIPT References: [1] P. Schwaller, F.J. Haug, J. Michler, J. Patscheider, Adv. Eng. Mater. 7 (2005) 318–

PT

322.

RI

[2] B. Navinšek, P. Panjan, I. Milošev, Surf. Coat. Technol. 97 (1997) 182–191. [3] Y.L. Su, S.H. Yao, Z.L. Leu, C.S. Wei, C.T. Wu, Wear 213 (1997) 165–174.

SC

[4] E. Kelesoglu, C. Mitterer, M.K. Kazmanli, M.Ürgen, Surf. Coat. Technol. 116–119

NU

(1999) 133–140.

[5] Y.H. Cheng, T. Browne, B. Heckerman, Wear 271 (2011) 775– 782.

MA

[6] L. Jianliang, Zh. Ningyi, W.D. Sproul, J.J. Moore, Surf. Coat. Technol. 206 (2012) 3283–3290.

TE

D

[7] L. Shan, Y. X. Wang, J. L. Li, X. Jiang, J. M. Chen, Tribol. Int. 82 (2015) 78–88. [8] J.L. Mo, M.H. Zhu, Appl. Surf. Sci. 255 (2009) 7627–7634.

AC CE P

[9] G.G. Fuentes, M.J. Diaz de Cerio, J.A. Garcia, R. Martinez, R. Bueno, R.J. Rodriguez, M. Rico, F.

Montala, Y. Qin, Thin Solid Films 517 (2009) 5894–5899. [10] F. Seibert, M. Dobeli, D.M. Fopp-Spori, K. Glaentz, H. Rudigier, N. Schwarzer, B. Widrig, J. Ramm, Wear 298–299 (2013) 14–22. [11] X. Zhu, D. Yue, C. Shang, M. Fan, B. Hou, Surf. Coat. Technol. 228 (2013) S184– S189. [12] A. Gilewicz, B. Warcholinski, D. Murzynski, Surf. Coat. Technol. 236 (2013) 149– 158. [13] R.A. Koshy, M.E. Graham, L.D. Marks, Surf. Coat. Technol. 202 (2007) 1123–1128.

14

ACCEPTED MANUSCRIPT [14] M. Setoyama, A. Nakayama, M. Tanaka, N. Kitagawa, T. Nomura, Surf. Coat. Technol. 86–87 (1996) 225–230.

PT

[15] A. Madan, I.W. Kim, S.C. Cheng, P. Yashar, V.P. Dravid, S.A. Barnett, Phys. Rev.

RI

Lett. 78 (9) (1997) 1743–1746.

[16] M. Stueber, H. Holleck, H. Leiste, K. Seemann, S. Ulrich, C. Ziebert, J. Alloys

SC

Comp. 483 (2009) 321–333.

NU

[17] R.A. Koshy, M.E. Graham, L.D. Marks, Surf. Coat. Technol. 204 (2010) 1359– 1365.

MA

[18] A. Gilewicz, B. Warcholinski, Surf. Coat. Technol. 279 (2015) 126–133. [19] B. Bouaouina, A. Besnard, S.E. Abaidia, F. Haid, Appl. Surf. Sci. (2016) in press.

(2015) 117–124.

TE

D

[20] M.I. Yousaf, V.O. Pelenovich, B. Yang, C.S. Liu, D.J. Fu. Surf. Coat. Technol. 265

AC CE P

[21] R. Lide, CRC Handbook of Chemistry and Physics (CRC Press LLC, New York, 2004) Sect.4, p.70.

[22] C. Ducros, F. Sanchette, Surf. Coat. Technol. 201 (2006) 1045–1052. [23] Q.N. Meng, M. Wen, C.Q. Hu, Surf. Coat. Technol. 206 (2012) 3250–3257. [24] W.D. Sproul, Science 273 (1996) 889–892. [25] S.K. Kim, V.V. Le, Surf. Coat. Technol. 204 (2010) 3941–3946. [26] F. Zhou, K. Chen, M. Wang, X. Xu, H. Meng, M. Yu, Zh. Dai, Wear 265 (2008) 1029–1037. [27] W. Gulbinski, T. Suszko, W. Sienicki, B. Warcholinski, Wear 254 (2003) 129–135.

15

ACCEPTED MANUSCRIPT Figure captions Fig. 1. XRD patterns of CrN and MoN single layers and selected CrN/Mo2N coatings on

PT

steel substrates deposited at different SRS.

RI

Fig. 2. SEM surface morphology and cross-sectional images of CrN/Mo2N coating

SC

deposited at SRS of 2 rpm.

Fig. 3. Cross-sectional TEM image of CrN/Mo2N coating deposited at 6 rpm and its

NU

SAED taken from the image area.

MA

Fig. 4. HRTEM images of the 6 rpm CrN/Mo2N coating. The oval in Fig.4 (a) represents a nanoparticle in amorphous matrix, inset shows interplanar distances of CrN and Mo2N

TE

D

sublayers.

Fig. 5. AFM images of CrN/Mo2N coatings deposited at different SRS.

AC CE P

Fig. 6. RBS spectra and corresponding fitting to CrN/Mo2N coatings showing decreased bilayer period along with increased SRS. Fig. 7. SEM images of the wear tracks on the surface of the 3 rpm (a, c) and 6 rpm (b, d) samples at different scales.

16

ACCEPTED MANUSCRIPT Table 1. Chemical composition and structural parameters of the multistructures and single layers.

TE AC CE P 17

Roughness, nm

PT

3.3 5 4.5 5.3 5.2 5 5.3 5 5

RI

45 54 40 44 41 37 44 39 46

SEM/RBS bilayer period, nm 105/110 90/93 63/69 48/49 36/39 27/29 12/15

SC

55 34 27 32 35 32 35 29

NU

46 26 29 27 28 24 26 25

Thickness, μm

D

CrN MoN 1 1.5 2 3 4 5 6

Composition, at% Cr N Mo

MA

Srs, rpm

12.5 17 1.1 6.7 6.5 10.6 7.1 1.7 5.7

ACCEPTED MANUSCRIPT Table 2. Mechanical and tribological properties of the multistructures and single layers. Critical load Lc2, N 65 ± 3

MoN

27 ± 2

-4.1 ± 0.3

96 ± 3

1

29 ± 2

-4.6 ± 0.4

29 ± 2

1.5

26 ± 2

-3.6 ± 0.3

2

27 ± 3

-3.6 ± 0.2

3

25 ± 2

-3.3 ± 0.4

4

24 ± 3

-1.8 ± 0.2

5

25 ± 2

6

23 ± 2

Coefficient of friction 0.53 ± 0.03

Wear rate, 10-7 mm3/Nm 13.6 6.5

0.35 ± 0.01

8.2

40 ± 3

0.34 ± 0.01

7.3

61 ± 4

0.29 ± 0.02

7.2

55 ± 5

0.33 ± 0.01

6.9

70 ± 4

0.34 ± 0.01

7.4

-2.6 ± 0.2

57 ± 5

0.34 ± 0.02

7.5

-1.8 ± 0.3

65 ± 3

0.33 ± 0.01

6.8

SC

RI

0.33 ± 0.01

NU

CrN

AC CE P

TE

D

MA

Nanohardness, GPa

PT

23 ± 1

Residual stress, GPa -6.2 ± 0.2

Srs, rpm

18

CrN (311)

Mo 2N (311)

(220)

CrN/Mo 2N

6rpm

Intensity (a.u.)

PT

(200)

CrN/Mo 2N

(111)

CrN/Mo 2N

ACCEPTED MANUSCRIPT

40

50

60

2rpm CrN

(400)

SC (220)

NU

(202)

MA

30

(200)

(002)

RI

5rpm

MoN

70

80

90

D

(deg)

TE

Fig. 1. XRD patterns of CrN and MoN single layers and of CrN/Mo2N coatings on steel substrates

AC CE P

deposited at different SRS.

19

NU

SC

RI

PT

ACCEPTED MANUSCRIPT

Fig. 2. SEM surface and cross-sectional images of CrN/Mo2N coating deposited at

AC CE P

TE

D

MA

SRS of 2 rpm.

20

D

MA

NU

SC

RI

PT

ACCEPTED MANUSCRIPT

TE

Fig. 3. Cross-sectional TEM image of CrN/Mo2N coating deposited at 6 rpm and its SAED taken

AC CE P

from the image area.

21

AC CE P

TE

D

MA

NU

SC

RI

PT

ACCEPTED MANUSCRIPT

Fig. 4. HRTEM images of the 6 rpm CrN/Mo2N coating. The oval in Fig.4 (a) represents a nanoparticle in amorphous matrix, inset shows interplanar distances of CrN and Mo2N sublayers.

22

AC CE P

TE

D

MA

NU

SC

RI

PT

ACCEPTED MANUSCRIPT

Fig.5. AFM images of CrN/Mo2N coatings deposited at different SRS.

23

AC CE P

TE

D

MA

NU

SC

RI

PT

ACCEPTED MANUSCRIPT

Fig. 6. RBS spectra and corresponding fitting to CrN/Mo2N coatings showing decreased bilayer period along with increased SRS.

24

TE

D

MA

NU

SC

RI

PT

ACCEPTED MANUSCRIPT

AC CE P

Fig. 7. SEM images of the wear tracks on the surface of the 3 rpm (a, c) and 6 rpm (b, d) samples at different scales.

25

ACCEPTED MANUSCRIPT Highlights CrN/Mo2N multilayered hard coatings were synthesized by cathodic-arc ion

PT

plating

RI

Influence of rotation speed on structure and mechanical properties is studied

SC

Rutherford backscattering spectrometry is utilized to examine the

NU

multistructures

AC CE P

TE

D

MA

Enhanced residual stress (~ -4.6 GPa) and critical load (~ 70 N) are observed

26