Papers

ICMCTF2002 Session E2-1: Wear Resistance of Ceramic, Metallic and Composite Coatings

Wednesday, April 24, 2002 1:30 PM in Room California

Wednesday Afternoon

Start	Invited?	Item
1:30 PM		E2-1-1 Tribological Aspects of Modelling Stresses and Fracture in Thin Coatings K. Holmberg, A. Laukkanen, H. Ronkainen, K. Wallin, S. Varjus (VTT, Finland) A general approach to controlling and modelling friction and wear in sliding contacts with coated surfaces is presented. The tribological aspects of the main material parameters, elasticity, plasticity and fracture is discussed. The contact conditions with a sphere sliding over a plate coated with a very thin coating is analysed. The dominant parameters for friction and wear performance is identified and the appropriate material parameters needed for controlling the tribological contact is proposed. A 3D Finite Element Model has been developed for calculating the first principal stress distribution in the scratch tester contact of a diamond spherical tip moving with increased load on a titanium nitride (TiN) coated steel surface. The model is comprehensive in that sense that it considers elastic, plastic and fracture behaviour of the contacting surfaces. Three main regions of stress concentration during the scratching action is identified. The loading mechanisms and the stress development in each of these regions is described. The first cracks to occur in a TiN coated steel plate sliding against a spherical diamond tip are due to the high stresses in the side-stress region and they are in an angular direction to the formed contact groove at the side edge of the groove. This corresponds to empirical observations. By identifying from a scratch experiment the location of the first crack and using this as input data can the fracture toughness of the coating can be determined. .
2:10 PM		E2-1-3 Buckle Delamination in Compressed Thin Films A.G. Evans (Princeton University) Compressed thin films are susceptible to failure by the formation and propagation of telephone cord buckles. Experimental observations of the formation and propagation of such buckles are presented for thin DLC films on glass substrates. A mechanics analysis is presented that relates the occurrence of the buckles to surface imperfections and their propagation to the energy release rate at the front and sides, as it relates to the dependence of interface toughness on mode mixity. The focused ion beam is used to section through the buckles in order to evaluate the residual stress in the DLC, enabling comparison between the measurements and the mechanics. This assessment is followed by a presentation of results for DLC films on steel substrates that demonstrate related phenomena.
2:50 PM		E2-1-5 Mechanical Properties of Particle Filled Sol-Gel Coatings on Glass G. de With, J. Malzbender (Consultant) In many cases coatings are important to modify functional properties of materials. In nearly all these cases the mechanical properties of the coatings are important. These properties can be assessed using indentation or scratch testing. This allows parameters such as the elastic modulus, hardness, residual stress and the fracture toughness to be determined. A simple, systematic and reproducible procedure with special consideration of thin ‘soft’ films has been long lacking. The present research attempts to provide such a procedure.
3:30 PM		E2-1-7 Defined YOUNG's Modulus Profile of Thin Films for Increased Load Carrying Capacity F. Richter, N. Schwarzer, V. Linss, I. Hermann, T. Chudoba (TU Chemnitz, Germany) At ICMCTF 2000, one of us gave a talk [1] and suggested a special coating design for increased load carrying capacity. Based on elastic analysis, in a first approximation the design was characterised by certain depth profiles of YOUNG´s modulus depending on film and substrate properties as well as on the applied load conditions. By utilising our completely analytical method, modulus profiles for special cases have been calculated in order to enable experimental verification of the concept. A second necessary condition for the experimental realisation of "modulus graded" films is the availability of a suitable thin film material which makes it possible to adjust its YOUNG´s modulus within a broad range. A material system having these properties was found in the ternary triangle B-C-N. By reactive magnetron sputtering of targets with different B/C ratio in nitrogen containing gas mixtures films with a YOUNG´s modulus ranging from 100 GPa up to more than 300 GPa can be produced. The modulus was found to be adjustable by both the substrate bias voltage and the Ar/N₂ ratio of the working gas, respectively [2]. The concept was proofed by spherical indentation measurements using an UMIS 2000 system. Here, it had to be taken into consideration that changing YOUNG´s modulus is usually connected with a modification of the critical yield stress. Hence, the modulus profile is only a first step in developing the optimum layer design. Modelling based on the ELASTICA software [3] was used in order to interpret the measuring data. Both single layers and multilayers were investigated [4]. The feasibility of the predicted approach could be confirmed. [1] N. Schwarzer: paper E2-10, ICMCTF 2000, San Diego, USA, April 2000, published in Surf. Coat. Technol. 133 -134 (2000) 397 - 402. [2] V. Linss et al., this conference. [3] T. Chudoba, N. Schwarzer: trial version of Elastica© at http/www.tu-chemnitz.de/~thc. [4] I. Hermann et al., this conference.
3:50 PM		E2-1-8 On a Wear Model of Multilayer Hard Coatings M. Dudek (University of LODZ, Poland); S. Fouvry (Ecole Centrale de Lyon, CNRS, France); B. Wendler (University of LODZ, Poland) Due to peculiar oxidation and wear resistance properties, multilayer hard coatings are extensively employed in machining and other mechanical industries. Contrary to monolayer systems, few models have been developed to predict the wear endurance of such systems. The purpose of this paper is, by transposing a local dissipated energy wear approach, to establish the wear prediction of multilayer based on the quantification of the monolayer coatings. Considering a dry reciprocating condition, TiC and VC hard coatings have been deeply analyzed in terms of friction and wear responses. For similar loading conditions, alternated TiC-VC multilayer systems consisting from 2 to 200 superimposed monolayers have been investigated. It was shown that above 10 monolayers (i.e. monolayer thickness inferior to 0.4 µm), diffusion mechanisms generate complex carbide structures which displays lower wear resistance than the corresponding monolayer carbide coatings. Above this critical thickness, monolayer alternance is less degraded and the multilayer response will depend on the position of the contact interface through the superimposed carbide structure. When the interface is located through a given carbide layer, the multilayer system displays a wear and friction behavior equivalent to the corresponding monolayer coating. Considering TiC and VC coating behaviors it becomes possible to reconstruct the wear evolution of TiC-VC multilayer systems by transposing a global wear dissipated energy approach. Decreasing the superimposed monoloyer thickness, the multilayer system displays a more complex behavior where the different carbide layers interfere on the contact response. To quantify such wear and tribological behavior, a new approach is developed which consists to combine a composite description of the interface with a local energy quantification of wear phenomena. Experiments and modeling are compared in order to establish the reliability and the limit of the approach.
4:10 PM		E2-1-9 Wear Mechanism Assessment of Low-Friction Carbon Coatings O. Ajayi, A. Kovalchenko, A. Erdemir, G. Fenske (Argonne National Laboratory) Amorphous carbon coatings with very low friction properties were recently developed at Argonne National Laboratory. These coatings have shown good promise in mitigating excessive wear and scuffing problems associated with low-lubricity diesel fuels. In the present study, we evaluated the friction and wear as well as failure mechanism attributes of three variations of the coating under a boundary lubrication regime. Tests were conducted with both synthetic and mineral oil lubricants using a ball-on-flat contact configuration in reciprocating sliding. Although the three variations of the coating provided modest reductions in friction coefficient, they all reduced wear substantially compared to uncoated surface. The scuffing performance of carbon coated H-13 steel surfaces also were evaluated using the same contact configuration and lubricants. We found that the scuffing resistance increased significantly when one of the sliding surfaces was coated. Improvement in scuffing resistance was more pronounced in the tests conducted with the base-stock oil because extreme pressure (EP) additive was not present in the lubricant. The wear and damage mechanisms under boundary lubrication in the three variation of coating were assessed. The impact of thickness, adhesion and hardness of coating on failure/wear mechanism are discussed.
4:30 PM		E2-1-10 Low-friction TiN and Ti(C,N) Coatings Deposited by PACVD M. Stoiber, G. Fontalvo, E. Badisch (Materials Center Leoben, Austria); C. Lugmair (Rübig GmbH & CoKG, Wels, Austria); A. Figueras (Univesitat Autonoma de Barcelona, Spain); C Mitterer (University of Leoben, Austria) TiN and Ti(C,N) coatings are the most frequently used hard coatings for industrial applications. Their protective properties like corrosion and wear resistance combined with their well investigated PVD and CVD processes make them a useful solution for increasing the lifetime of numerous working tools. In addition to high hardness there are several applications where low friction coefficients are required. Most hard coatings which show a typical friction coefficient in the range of 0.5 - 0.8 against steel can only fulfill those requirements in combination with solid lubricants like MoS₂ or DLC. The aim of this study was to develop TiN and Ti(C,N) coatings deposited by PACVD (plasma-assisted chemical vapor deposition) with optimized friction and wear properties. Coating structure and chemical composition were characterized using scanning electron microscopy (SEM) and wavelength dispersive electron probe microanalysis (EPMA). The tribological properties of the coatings were evaluated using a ball-on-disc tribometer and a microscale abrasion tester. Hardness measurements with a depth-sensing microhardness tester gave values of 38 GPa for TiN and 52 GPa for Ti(C,N). Extremely low friction coefficients against ball-bearing steel of 0.18 - 0.22 have been obtained for those TiN coatings showing a chlorine content in the range of 3.5 - 4 at.-%. For lower chlorine contents, the friction coefficient of TiN coatings increases to 0.6, whereas for Ti(C,N) coatings low values of about 0.17 have also been obtained for the lowest chlorine content measured (i.e. 2.7 at.-%). The wear tracks were investigated with an optical profiler and wear rates between 1.12x10^-16 and 0.69x10^-12 m²/N were observed for TiN (according to the chlorine content) and of 1.97x10^-16 m²/N for Ti(C,N).
4:50 PM		E2-1-11 Improvement of "Duplex" PVD Coatings for HSS Cutting Tools by PFPE (Perfluorpolyether "Z-DOL") G.S. Fox-Rabinovich (McMaster University, Canada); A.I. Kovalev, D.L. Wainstein (Surface Phenomena Research Group, Russia); G.K. Dosbaeva (McMaster University, Canada); L.S. Shuster (Ufa Aircraft Technological University, Russia) A high-speed steel of M2 type was hard-ened by ‘duplex’ technology (ion nitriding followed by TiN PVD coating). The ‘duplex’ coating was further modified by application of a PFPE (perfluoropolyether Z-DOL) layer at the surface. The tribological parameters of the coating and the changes in composition and fine (atomic level) structural characteristics of the tool surface with a multi-layered coating were investigated. It was found that the decrease of the friction parameter and significant decrease of the surface layer damage is caused by an electro-static screening of the surface by the lubricant. Simultaneously a process of self-organizing occurs during the running-in stage of the wear of the cutting tool surface with the multi-layered coating. Several parallel phenomena develop during this self-organizing process: (a) tribodecomposition of the thin surface layer: (b) formation of a stable amorphous-like protective layer (of Ti-O and Ti-F types) on the tool surface. All these processes improve the wear stability during the running-in stage of wear, leading to increased tool life.
5:10 PM		E2-1-12 The Role of Mass Transfer Layer on the Tribological Characteristics of Silver-coated Surfaces. S.H. Yang, H. Kong, E.-S. Yoon (Korea Institute of Science and Technology, Korea); D.E Kim (Yonsei University, Korea) Film failure is regarded as a definite end of service life of coated surfaces. However, the authors showed in recent works that friction could be low and stable even after initial failure of coating film. It was argued that mass transfer layer played an important role on the decrease in friction. In this paper, the tribological role of transfer layer was studied further with various types of silver coatings under various ranges of load and sliding speed and different environment conditions. Silver coatings were performed with thermal evaporation, ion beam assisted deposition and atomic mixing method. Tests were performed in dry sliding conditions, using a ball-on-disk contact configuration, at the load of 0.0196-17.64 N and the sliding speed of 20-1,000 mm/sec. Results showed that tribological behavior was affected significantly by the transfer layer formed at contact surfaces. SEM and EPMA analyses showed that contact surfaces were covered with mass transfer layers of agglomerated wear particles and they acted as a protective layer. It was also found that the decrease in friction and wear was mainly attributed to shakedown phenomena occurred at these layers. However, the formation of mass transfer layer was suppressed by several destructive actions as the sliding speed increased. Such that above a critical sliding speed, no mass transfer layer was able to form. For building up a general framework of tribological behavior of silver coated films, all test data were summarized on a map whose axes are contact pressure and sliding speed. As a result, three main regimes were clearly identified: (i) elastic/plastic deformation of silver coating without failure, (ii) mild wear regime after the failure of silver coating and (iii) severe wear regime after the coating failure.