Microstructure and mechanical properties of PVD

Solid State Phenomena Vol. 186 (2012) pp 230-233 Online available since 2012/Mar/15 at www.scientific.net © (2012) Trans Tech Publications, Switzerland doi:10.4028/www.scientific.net/SSP.186.230

Microstructure and mechanical properties of PVD nanoncrystalline layers Krzysztof Lukaszkowicz1,a, Jarosław Konieczny1,b 1

Institute of Engineering Materials and Biomaterials, Konarskiego 18A Street, 44-100 Gliwice, Poland a

[email protected], [email protected]

Keywords: nanostructural coating, PVD, tool materials, adhesion, mechanical properties.

Abstract. This work presents the research results on the structure and mechanical properties of coatings deposited by PVD methods on the X40CrMoV5-1 hot work tool steel substrates. It was found that tested coatings have nanostructural character with fine crystallites, while their average size fitted within the range 10–15 nm, depending on the coating type. The morphology of the fracture of coatings is characterized by a dense microstructure. The coatings demonstrated good adhesion to the substrate, the latter not only being the effect of interatomic and intermolecular interactions, but also by the transition zone between the coating and the substrate, developed as a result of diffusion and high-energy ion action that caused mixing of the elements in the interface zone and the compression stresses values. The critical load LC2 lies within the range 66–85 N, depending on the coating type. The coatings demonstrate a high hardness (4000 HV). Introduction Looking for coating materials with hardness which is higher than the hardness of traditional polycrystalline coatings, there are founding materials with unique nanometric structure properties. Hardness of materials increases with decreasing the size of grains. This is due to the declining dislocation movement. The critical grain size value in the mechanical tension zone of the material, which fulfill the Hall-Petch relation for polycrystalline microstructures, which is equal 10 nm. For grains with diameters less than the critical value the material should be “softened” due to the action of a new deformation mechanism. i.e., the Hall – Petch relation is inverted [1]. Nanostructural coatings deposited by physical vapour deposition (PVD) are recognised as one of very interesting premium technologies for modification and protection of products surface, for the reason of the existing possibility to synthesis materials with unique physical and chemical properties. This coatings are characterized by: extremely high indentation hardness (4000-8000 HV) [2-3], excellent high temperature oxidization resistance [4, 5], high abrasion and erosion resistance [6-8], as well corrosion resistance [9]. Nanostructural coatings as a modern kind of layers are applied mainly for wear protection of machining tools, reduction of friction in sliding parts and to increase their life time and properties. The aim of this paper is to examine the microstructure and mechanical properties of nanostructure coatings deposited by PVD technique on the X40CrMoV5-1 hot work tool steel substrate. Experimental procedures The tests were made on samples of the X40CrMoV5-1 hot work tool steel deposited with CrAlSiN+DLC, and AlTiCrN+DLC coatings. The CrAlSiN and AlTiCrN coating deposition process was made in a device based on the cathodic arc evaporation method in an Ar and N2 atmosphere. Cathodes containing pure metals (Cr, Ti) and the AlSi (88:12 wt%) and TiAl (50:50 at%) alloys were used for deposition of the coatings. The DLC (diamond-like carbon) topcoat was deposited using acetylene (C2H2) as precursor in order to reduce of friction. The DLC coating was produced by PACVD (Plasma Assisted Chemical Vapor Deposition) process. The deposition conditions are summarized in Table 1. All rights reserved. No part of contents of this paper may be reproduced or transmitted in any form or by any means without the written permission of TTP, www.ttp.net. (ID: 157.158.79.131, Silesian University of Technology, Gliwice, Poland-16/07/13,14:04:46)

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Table 1. Deposition parameters of the coatings. Parameters Base pressure [Pa] Working pressure [Pa] Substrate bias voltage [V]

CrAlSiN 510-3 4.5 -40

Target current [A]

Cr – 70 AlSi – 120

Process temperature [ºC]

450

AlTiCrN 510-3 2,5 -50 TiAl – 120 Cr – 140 Ti – 120 430

DLC 110-3 2 -500 – 220

Structure of coatings was tested with the use of the JEOL JEM 3010 UHR transmission electron microscope, at 300 kV bias voltage. The thin foils of coatings were produced as a result of mechanical thinning and further ionic polishing using the Gatan apparatus. Observations microstructure of the deposited coatings were carried out on cross sections in the SUPRA 25 scanning electron microscope. The X-ray line broadening technique was used to determine the average crystallite size of the coatings using Scherrer formula with silicon as internal standard. The microhardness was measure on cross section of coatings by the SHIMADZU DUH 202 ultramicrohardness tester. The test conditions were selected in order as to be comparable for all coatings. Measurements were made with 25 mN load. Tests of the coatings’ adhesion to the substrate material were made using the scratch test on the CSEM REVETEST device. The tests were made using the following parameters: load range - 0–100 N, load increase rate (dL/dt) - 100 N/min, indenter’s sliding speed (dx/dt) - 10 mm/min, acoustic emission detector’s sensitivity AE - 1. Results and discussion The coatings present a compact structure, without any visible delaminations or defects (Figs. 1, 2). The morphology of the fracture of coatings is characterized by a dense (in case of CrAlSiN and DLC layers) and columnar (in case of AlTiCrN layer) microstructure. The deposited coatings show a sharp transition zone between the substrate and the layers. The morphology of the coatings’ surfaces is characterized by a significant inhomogeneity connected with occurrences of the micro droplets (Fig. 1), which is connected with the essence of the used cathodic arc evaporation method for depositing the coatings. The thickness of the based and DLC layers are given in Table 2.

Fig. 1. SEM fracture image of AlTiCrN+DLC Fig. 2. SEM fracture image of CrAlSiN+DLC coating deposited onto the X40CrMoV5-1 steel coating deposited onto the X40CrMoV5-1 steel substrate. substrate.

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The hardness of the X40CrMoV5-1 steel substrate without coating is 630 HV (56 HRC), as settled upon hardness tests. The deposition of the AlTiCrN and CrAlSiN based coatings onto the substrates causes the growth of hardness of the surface layer ranging from 3400 to 4000 HV (Table 2). The hardness of the DLC top layer is 2000 HV. The critical load values LC1 and LC2 were determined by the scratch test method (Fig. 3). The load at which the first coating defects appear is known as the first critical load LC1. The first critical load LC1 corresponds to the point at which first damage is observed; the first appearance of microcraking, surface flaking outside or inside the track without any exposure of the substrate material – the first cohesion – related failure event. LC1 corresponds to the first small jump on the acoustic emission signal, as well as on the friction force curve (Fig. 3). The second critical load LC2 is the point at which complete delamination of the coatings starts; the first appearance of cracking, chipping, spallation and delamination outside or inside the track with the exposure of the substrate material – the first adhesion related failure event. After this point the acoustic emission graph and friction forces have a disturbed run (become noisier). The cumulative specification of the test results are presented in Table 2. Load force Fn, N

LC1

80

LC2 Ft

60 40

AE

20 0 0

1

2

3

4 5 6 Path X, mm

7

8

100 90 80 70 60 50 40 30 20 10 0

nn

100

Acoustic emission AE

Friction force Ft, N ggg

0 10 20 30 40 50 60 70 80 90 100

9

Fig. 3. Diagram of the dependence of the acoustic emission (AE) and friction force Ft on the load for the X40CrMoV5-1 steel with the AlTiCrN+DLC coating. Table 2. The characteristics of the investigated coatings. Thickness [μm]

Crystallite size [nm]

Microhardness [HV]

Critical load LC1 [N]

Critical load LC2 [N]

CrAlSiN/DLC

2.0/1.3

10

4000/2000

25

85

AlTiCrN/DLC

1.2/1.9

15

3400/2000

26

66

Coating

Fig. 4. TEM bright-field images and electron Fig. 5. TEM bright-field image and electron diffraction patterns of AlTiCrN coating. diffraction patterns of CrAlSiN coating.

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Transmission electron microscopy (TEM) examination of the coatings showed that they consisted of fine crystallites (Figs. 4, 5). Solution of the diffraction pattern from areas visible in Figure 4 and 5 are allowed to identify the phase present in the area of the microstructure of the coating. In both cases it is a nitride (CrAlSi)N and (AlTiCr)N, crystallising in the crystal lattice of face-centered cubic cell. Basing on observations in the bright and dark fields and analysis of the results obtained using Scherer method, an average size of crystallites in the investigated coatings were evaluated as about 10-15 nm. Summary The AlTiCrN+DLC and CrAlSiN+DLC, coatings were deposited successfully on X40CrMoV5-1 hot work tool steel substrate. The compact microstructure of the coatings without any visible delamination was observed in the scanning electron microscope. Based on the coatings investigation in the transmission electron microscope, it was observed that the coatings have nanostructural character with fine crystallites which size is 10–15 nm. The scratch tests on coating adhesion reveal the cohesive and adhesive properties of the coatings deposited on the substrate material. In virtue of the tests carried out, it was found that the critical load LC2 fitted within the range 66–85 N for the coatings deposited on a substrate made of hot work tool steel X40CrMoV5-1. Acknowledgment Research was financed partially within the framework of the Polish State Committee for Scientific Research Project No N507 550 738 headed by Krzysztof Lukaszkowicz, PhD. References [1] S. Zhang, N. Ali (eds.): Nanocomposite Thin Films and Coatings, 2007, London, Imperial College Press. [2] S. Veprek, M.G.J. Veprek-Heijman: The formation and role of interfaces in superhard ncMenN/a-Si3N4 nanocomposites, Surface and Coatings Technology 201 (2007) 6064-6070. [3] C.W. Zou, H.J. Wang, M. Li, Y.F. Yu, C.S. Liu, L.P. Guo, D.J. Fu: Characterization and properties of TiN-containing amorphous Ti–Si–N nanocomposite coatings prepared by arc assisted middle frequency magnetron sputtering, Vacuum 84 (2010) 817-822. [4] F. Vaz, L. Rebouta, P. Goudeau, J. Pacaud, H. Garem, J.P. Riviere, A. Cavaleiro, E. Alves: Characterisation of Ti1-xSixNy nanocomposite films, Surface and Coatings Technology 133-134 (2000)307-313. [5] A.A. Voevodin, J.S. Zabinski: Nanocomposite and nanostructured tribological materials for space applications, Composites Science and Technology 65 (2005) 741-748. [6] S. Veprek, M.J.G. Veprek-Heijman: Industrial applications of superhard nanocomposite coatings, Surface and Coatings Technology 202 (2008) 5063-5073. [7] Y.C. Cheng, T. Browne, B. Heckerman, E.I. Meletis: Mechanical and tribological properties of nanocomposite TiSiN coatings, Surface and Coatings Technology 204 (2010) 2123-2129. [8] K. Polychronopoulou, M.A. Baker, C. Rebholz, J. Neidhardt, M. O`Sullivan, A.E. Reiter, K. Kanakis, A. Leyland, A. Matthews, C. Mitterer: The nanostructure, wear and corrosion performance of arc-evaporated CrBxNy nanocomposite coatings, Surface and Coatings Technology 204 (2009) 246-255. [9] K. Lukaszkowicz, J. Sondor, A. Kriz, M. Pancielejko, Journal of Materials Science 45 (2010) 1629-1637.

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Microstructure and Mechanical Properties of PVD Nanoncrystalline Layers 10.4028/www.scientific.net/SSP.186.230 DOI References [1] S. Zhang, N. Ali (eds. ): Nanocomposite Thin Films and Coatings, 2007, London, Imperial College Press. doi:10.1142/9781860949975 [2] S. Veprek, M.G.J. Veprek-Heijman: The formation and role of interfaces in superhard nc- MenN/a-Si3N4 nanocomposites, Surface and Coatings Technology 201 (2007) 6064-6070. doi:10.1016/j.surfcoat.2006.08.112 [3] C.W. Zou, H.J. Wang, M. Li, Y.F. Yu, C.S. Liu, L.P. Guo, D.J. Fu: Characterization and properties of TiN-containing amorphous Ti–Si–N nanocomposite coatings prepared by arc assisted middle frequency magnetron sputtering, Vacuum 84 (2010) 817-822. doi:10.1016/j.vacuum.2009.10.050 [6] S. Veprek, M.J.G. Veprek-Heijman: Industrial applications of superhard nanocomposite coatings, Surface and Coatings Technology 202 (2008) 5063-5073. doi:10.1016/j.surfcoat.2008.05.038 [7] Y.C. Cheng, T. Browne, B. Heckerman, E.I. Meletis: Mechanical and tribological properties of nanocomposite TiSiN coatings, Surface and Coatings Technology 204 (2010) 2123-2129. doi:10.1016/j.surfcoat.2009.11.034 [8] K. Polychronopoulou, M.A. Baker, C. Rebholz, J. Neidhardt, M. O`Sullivan, A.E. Reiter, K. Kanakis, A. Leyland, A. Matthews, C. Mitterer: The nanostructure, wear and corrosion performance of arc-evaporated CrBxNy nanocomposite coatings, Surface and Coatings Technology 204 (2009). doi:10.1016/j.surfcoat.2009.07.009 [9] K. Lukaszkowicz, J. Sondor, A. Kriz, M. Pancielejko, Journal of Materials Science 45 (2010) 1629-1637. doi:10.1007/s10853-009-4140-1