In this paper, we present the results of a study of TiN thin films which are deposited by a Physical Vapour Deposition (PVD) and Ion Beam Assisted Deposition (IBAD). In the present investigation the subsequent ion implantation was provided with N+2 ions. The ion implantation was applied to enhance the mechanical properties of surface. The thin film deposition process exerts a number of effects such as crystallographic orientation, morphology, topography, densification of the films. The evolution of the microstructure from porous and columnar grains to densel packed grains is accompanied by changes in mechanical and physical properties. A variety of analytic techniques were used for characterization, such as scratch test, calo test, Scanning electron microscopy (SEM), Atomic Force Microscope (AFM), X-ray diffraction (XRD) and Energy Dispersive X-ray analysis (EDAX).U ovom radu pretstavljaju se rezultati istraživanja TiN tankih fi lmova, nanešenih fi zičkim odlaganjem iz parne faze i te podržani ionskim snopom. U ovom istraživanju je izvršena i naknadna ionska primjena sa N+2 ionima. Ionska primjena je sprovedena radi poboljšanja mehaničkih svojstava površina. Proces nanošenja tankih fi lmova karakterizira veliki broj učinaka, kao što su: kristalografska orijentacija, morfologija, topografi ja, gustoća fi lma. Razvoj mikrostrukture od porozne i stubaste u zrnastu gusto pakovanu, se dešava uz istovremenu promjenu mehaničkih i fi zičkih svojstava. Za karakterizaciju su rabljene različite analitičke tehnike, kao što su test zaparavanja, kalo test, skenirajući elektronski mikroskop (SEM), mikroskop atomskih sila (AFM), rentgenska difrakcija X zraka (XRD) i energijska disperzivna analiza X zraka (EDAX)

A. Miletić

B. Škorić

D. Ješić

D. Kakaš

M. Gostimirović

Hrčak - Portal of scientific journals of Croatia

87METALURGIJA 51 (2012) 1, 87-90B. ŠKORIĆ, D. KAKAŠ, D. JEŠIĆ, M. GOSTIMIROVIĆ, A. MILETIĆCHARACTERIZATION OF DUPLEX HARD COATINGS WITH ADDITIONAL ION IMPLANTATIONReceived – Primljeno: 2011-01-25Accepted – Prihvaćeno: 2011-04-10Preliminary Note – Prethodno priopćenjeISSN 0543-5846METABK 51(1) 87-90 (2012)UDC – UDK 669.14.018:624.793:620.178.1:537.57=111In this paper, we present the results of a study of TiN thin fi lms which are deposited by a Physical Vapour Deposition (PVD) and Ion Beam Assisted Deposition (IBAD). In the present investigation the subsequent ion implantation was provided with N2+ ions. The ion implantation was applied to enhance the mechanical properties of surface. The thin fi lm deposition process exerts a number of eff ects such as crystallographic orientation, morphology, topography, densifi cation of the fi lms. The evolution of the microstructure from porous and columnar grains to densel packed grains is accompanied by changes in mechanical and physical properties. A variety of analytic techniques were used for characterization, such as scratch test, calo test, Scanning electron microscopy (SEM), Atomic Force Microscope (AFM), X-ray diff raction (XRD) and Energy Dispersive X-ray analysis (EDAX). Key words: steel, coating, super hard, ion implantation, nanohardnessKarakterizacija dupleks tvrdih prevlaka sa dodatnom ionskom primjenom. U ovom radu pretstavljaju se  rezul-tati istraživanja TiN tankih fi lmova, nanešenih fi zičkim odlaganjem iz parne faze i te podržani ionskim snopom. U ovom istraživanju je izvršena i naknadna ionska primjena sa N2+ ionima. Ionska primjena je sprovedena radi poboljšanja mehaničkih svojstava površina. Proces nanošenja tankih fi lmova karakterizira veliki broj učinaka, kao što su: kristalo-grafska orijentacija, morfologija, topografi ja, gustoća fi lma. Razvoj mikrostrukture od porozne i stubaste u zrnastu gusto pakovanu, se dešava uz istovremenu promjenu mehaničkih i fi zičkih svojstava. Za karakterizaciju su rabljene različite analitičke tehnike, kao što su test zaparavanja, kalo test, skenirajući elektronski mikroskop (SEM), mikroskop atomskih sila (AFM), rentgenska difrakcija X zraka (XRD) i energijska disperzivna analiza X zraka (EDAX).Ključne rječi: čelik, prevlake, supertvrdoća, ionska primjena, nanotvrdoćaINTRODUCTIONThe various deposition techniques of coatings and process parameters differ widely in morphology and microstructure, in phases, grain size, texture, defects, im purity content, state of stress, and their mechanical and tribological properties.Ion bombardment during physical vapour deposition (IBAD) has more independent parameters than classic plasma based technique (PVD). The fi lm deposition process exerts a number of effects such as crystallo-graphic orientation, morphology, topography, densifi ca-tion of the fi lms [1]. However, the adhesion, structure and durability of coatings on various substrates can be substantially improved by irradiating the sub-strates and the condensing fi lm with ions and energetic neutrals in the energy range of several electron volts [2]. One of the most widely used physical vapour deposited coatings for engineering components is TiN.The adhesion strength transmits the surface loads into the component and takes up the stresses that arise B. Škorić, D. Kakaš, M. Gostimirović, A. Miletić, University of Novi Sad, Faculty of Technical Sciences, SerbiaD. Ješić, University of Banja Luka, Faculty of Engineering, Bosnia and Herzegovinabecause of the different properties of coating and sub-strate. The nitrided layers are a key issue in duplex coat-ing processing [3]. IBAD, can be used to control the preferred orientation and the properties of the TiN fi lm. IBAD has more independent parameters than a PVD technique and it is possible to study the effect of deposi-tion parameters on the structure of grown fi lms.The tribological performance of a component is governed by its design, environment, contact conditions and the materials of which it is composed [4]. The adhe-sion strength transmits the surface loads into the com-ponent and takes up the stresses that arise because of the different properties of coating and substrate. The three basic points that are considered fundamental to studies of friction are the surface area and nature of the intimate asperity contacts, the surface adhesion and shear stren-gth, and the nature of deformation and energy dissipa-tion occurring at the asperity junctions [5].Characteristics of surface layer structure as well as important properties were investigated. A variety of analytic techniques were used for characterization, such as scratch test, calo test, SEM, AFM, XRD and EDAX.EXPERIMENTAL PROCEDUREThe substrate material used was high speed steel type S 6-5-2. High-speed steel’s microstructure consists 88  METALURGIJA 51 (2012) 1, 87-90B. ŠKORIĆet al.: CHARACTERIZATION OF DUPLEX HARD COATINGS WITH ADDITIONAL ION IMPLANTATIONof large primary carbide particles, disappeared in tem-pered martensitic matrix containing a much fi ner dis-persion of secondary carbides.The specimens were fi rst austenized, quenched and then tempered to the fi nal hardness of 850 HV. In order to produce good adhesion of the coating, the substrates were plasma nitrided at low pressure. The used sputter-ing system allowed an ultimate pressure of about 5Pa.The PVD treatment was performed in a Balzers Spu-tron installation with rotating specimen. The deposition parameters were as follows: Base pressure in the cham-ber was 1×10−5 mbar, bias voltage Ub=1kV, discharge current Id=50mA, substrate temperature Ts=200 °C, tar-get to substrate distance ds–t=120 mm. The partial pres-sure of Ar during deposition was PAr=(3,1–6,6)×10−6 mbar and partial pressure of N2 was PN2=6,0×10−6–1,1×10−5 mbar. Deposition rate aD=0,1 nm/s. Prior to en-tering the deposition chamber the substrates were cleaned. The coatings (IBAD), were deposited with ion beam bombardment in a DANFYSIC chamber. The base pres-sure in the vacuum chamber was 10-4 Pa for all experi-ments. System has Kaufman-type ion source, sample holder and quartz crystal thickness monitor. A pure tita-nium intermediate layer with a thickness of about 50nm has been deposited fi rst for all the coatings to enhance the interfacial adhesion to the substrates. The ion energy (EAr=1,5–2 keV), ion beam incident angle (15°), target to substrate distance ds–t=360 mm, and substrate tempera-ture Ts=200 °C, were chosen as the processing variables. Deposition rate aD=0,05–0,25 nm/s. Quartz crystal moni-tor was used to gauge the approximate thickness of the fi lm. After deposition, the samples were irradiated with 120 keV N2+ ions at room temperature (RT). N2+ ions were supplied by an electron cyclotron resonance (ECR) ion source. The implanted fl uencies were in the range from 0,6×1017 to 1×1017 ions/cm2The mechanical properties on coated samples were characterized using a Nanohardness Tester (NHT) de-veloped by CSM Instruments. The NHT is especially suited to load and penetration depth measurements at nanometer length scales. The maximum indentation depth was fi xed at one tenth of the coating thickness. The analyzed AE signal was obtained by a scratch-ing test designed for adherence evaluation. Acoustic Emission (AE) is an important tool for the detection and characterisation of failures in the framework of non-de-structive testing. The analysed AE signal was obtained by a scratching test designed for adherence evaluation. Scratch tests were performed under controlled condi-tions with a device that consisted of a loaded probe with a diamond indenter moving linearly along the sample with a constant speed and continuously increasing force. The steadily increasing contact load causes tensile stress behind the indenter tip and compressive stress ahead of the cutting tip. Detection of elastic waves generated as a result of the formation and propagation of micro cracks. The AE sensor is insensitive to mechanical vi-bration frequencies of the instrument. This enables the force fl uctuations along the scratch length to be fol-lowed, and the friction coeffi cient to be measured. The scratch tester equipment with an acoustic sensor (CSM-REVETEST) was used. The stress determination follows the conventional sin2ψ method, using a PHILIPS XPert diffractometer.In the nanoindentation technique, hardness and Young’s modulus can be determined by the Oliver and Pharr method [6], where hardness (H) can be defi ned as: H=Pmax/A, where Pmax is maximum applied load, and A is contact area at maximum load. In nanoindentation, the Young’s Modulus, E, can be obtained from: 1/Er=(1-ν2)/E+(1-ν2)/Er, where νi=Poisson ratio of the diamond indenter (0.07) and Ei=Young’s modulus of the dia-mond indenter. Therefore, in recent years, a number of measurements have been made in which nanoindenta-tion and AFM have been combined. Indentation was performed with CSM Nanohardness Tester. The results are analyzed in terms of load-displacement curves, hardness, Young’s modulus, unloading stiffness and elastic recovery. The analysis of the indents was per-formed by Atomic Force Microscope. The stress deter-mination follows the conventional sin2ψ method, using an X-ray diffractometer. RESULTS AND ANALYSISThe analyzed nitrogen-to-metal ratio of the deposit-ed fi lms, with EDAX, is given in the Table 1.The nitrogen to metal ratio, EDX, is stoichiometries for IBAD technology and something smaller from PVD. For sample with additional ion implantation, value is signifi cantly different, smaller.Table 1 Atomic ratio N/Ti in coatingCoating Ratio N/Ti (atomic)1 IBAD 1,002 PVD 0,983 PVD/III 0,89It is possibly diffused from the layer of TiN to the interface. The TiN coatings only show a golden surface and after ion implantation the colour is dark golden.Vickers microhardness and nanohardness measure-ments of samples are given in Table 2.Table 2  Surface microhardness (HV0.03) and nanohardness (load-10mN).Unit pn/IBAD PVD pn/PVD/IIAv. Vickers 2 007 3 028 3 927Av. GPa 21,6 32,6 42,6The maximum nanohardness of coating measured by Berkovich indenter is about 42,6 GPa. All the results of nanohardness are obtained with the Oliver & Pharr method and using a supposed sample Poisson’s ratio of 0,3 for modulus calculation. A hardness increase is ob-served for implanted samples. This can be attributed to iron nitride formation in the near surface regions. 89METALURGIJA 51 (2012) 1, 87-90B. ŠKORIĆet al.: CHARACTERIZATION OF DUPLEX HARD COATINGS WITH ADDITIONAL ION IMPLANTATIONTypical surface image measured by AFM (Veeco dc II) is presented on Figure 1.For the practical applications of IBAD coatings, it is important to know that the roughness of the surface de-creased slightly after deposition (from Ra=0,19 µm to Ra=0,12 µm).The nanoindentation elastic modulus was calculated using the Oliver–Pharr data analysis procedure. The in-dividual values of E are the different for all measure-ments, Figure 2.The errors related to the measurements and estima-tions were different and for duplex coating with ion im-plantation is less than 4 %. Good agreement could be achieved between the Ec values and nanohardness.For each measurement, the penetration (Pd), the re-sidual penetration (Rd), the acoustic emission (AE) and the frictional force are recorded versus the normal load. The breakdown of the coatings was determined both by AE signal analysis and optical and scanning electron microscopy. AE permits an earlier detection, because the shear stress is a maximum at certain depth beneath the surface, where a subsurface crack starts. The critical load Lc3 corresponds to the load inducing the delami-nation of the coating, Figure 3. Coating is often in tensile stress with greater micro-hardness. During TiN fi lm growth, titanium atoms are fi rstly piled, as compact as possible, depending on the local conditions. The nitrogen atoms occupy the octahe-dric sites in varying number according to the energy that these atoms possess to cross the potential barriers created by the surrounding titanium anions. The tribological behaviour of the coatings was stud-ied also by means of pin-on-ring contact confi guration in dry sliding conditions, described elsewhere [7].The simplest form of X-ray diffraction (XRD) char-acterization of thin fi lm microstructure is Cohen-Wag-ner plot. A typical result for compact fi lm, with residual stresses σ = -4,28Gpa, is shown in Figure 4. The anisotropy of lattice parameters, ahhh>>ahoo, is characteristic for compact fi lm.The width of column is derived from the width of the diffraction peaks (Figure 5), (λ=0,154nm, θ=62.5o and β=0,056rad), and it is 70 nm.The (422) diffraction peak was recorded in a 2θ in-terval between 118º and 130º, with tilting angle. It is ob-served an increase in micro hardness with the (200) ori-entation degree [8]. These results are in agreement with those obtained in other paper [9]. The coating morphol-ogy was evaluated using the well-known structure zone model of Thornton. All observed morphologies are be-lieved to be from region of zone I (PVD) and from the border of region zone T (IBAD). It has been suggested [10], that the transition from open porous coatings with low micro hardness and rough surface, often in tensile stress, to dense coatings fi lms with greater micro hard-Figure 1  AFM image of a TiN coating implanted with nitrogen Figure 2 Young’s elastic module.Figure 3 Delamination of coatingFigure 4  The Cohen-Wagner plot, lattice parameters ahkl vs.cosθcot2θ.90  METALURGIJA 51 (2012) 1, 87-90B. ŠKORIĆet al.: CHARACTERIZATION OF DUPLEX HARD COATINGS WITH ADDITIONAL ION IMPLANTATIONness, smooth surface occures at a well defi ned critical energy delivered to the growing fi lm. The microstruc-ture of the TiN fi lm, Figure 6, shows a columnar struc-ture reaching from the substrate to the coating surface. The specimen for these investigation was broken and the fracture surfaces were inspected.CONCLUSIONSDeposition of TiN on plasma nitrided steel by IBAD process was successfully used to produce a hard sur-face. It was found that the plasma-nitriding process en-hanced the coating to substrates adhesion.The experimental results indicated that the mechani-cal hardness is elevated by penetration of nitrogen, whe-reas the Young’s modulus is signifi cantly elevated. Ni-trogen ion implantation leads to the formation of a hard surface layer.Coatings developed under this project should dem-onstrate performance that exceeds that of PVD coat-ings.Nitrogen implantation into hard TiN coatings sig-nifi cantly reduces the tendency of the coatings to form micro cracks when subjected to loads or stresses.The present coating method can produce dance structures and the high critical load values can be achieved. The above fi ndings show that deposition process and the resulting coating properties depend strongly on the additional ion bombardment.AcknowledgmentsThe authors would like to thank to The Scientifi c Council of Serbia supported this work by grant.REFERENCES[1] K. Mogensen, N. Thomsen, S. Esikilden, C. Mathiasen and J.Bottiger, Surface and Coatings Technology 99 (1998) 140-146. [2] W. Ensinger, Surface and Coatings Technology 99 (1998) 1-13.[3] Batista J.C.A.; Godoy C.; Matthews A.; Leyland A., Surfa-ce Engineering, 9 (2003) 37-44.[4] Sekulić, M. , Jurkovič, Z. , Hadžistevič, M., Gostimirovič, M, Metalurgija, 49 (2010) 4, 339-342.[4] J.P. Celis, Surface and Coating Technology, 74-75 (1995) 15-22.[5] Pharr, G.M., Oliver, W.C., Brotzen, F.R., J. Mater. Res.,7 (1992), 613.[6] B. Škorić, D. Kakaš and T. Gredić, Thin Solid Films, Else-vier Science, 317 (1988) 486-489.[7] K. H. Bäther, U. Herrmann, A. Schröer, Surface and Coa-ting Technology, 74-75 (1995) 793-801. [8] L. Combadiere, J. Machet, Surface and Coating Technolo-gy, 88 (1996) 28-37. [10]  M. Griepentrog, B. Mackrodt, G. Mark and T. Linz, Surfa-ce and Coatings Technology 74-75 (1995) 326-332.Note:  The responsible translator for the English language is Pal Terek, University of Novi Sad, SerbiaFigure 5 XRD diff raction peak of TiN(422)Figure 6  Surface morphologies of TiN(PVD) implanted with nitrogenθλθβλcoscos9.0=t

Karakterizacija dupleks tvrdih prevlaka sa dodatnom ionskom primjenom

Abstract

Similar works

Full text

Available Versions

Hrčak - Portal of scientific journals of Croatia