ICMCTF2014 Session EP: Symposium E Poster Session

In this paper microstructure and basic mechanical properties of WC-Co coatings obtained by HVOF and HVAF technique were shown. Standard powder of WC-Co 83-17 (Amperit 625.074) was used for coating deposition on steel substrate. Sub-microcrystalline TiC powder was used to modify coting deposited from Amperit 625.074.The aim of investigations was to compare microstructure and some mechanical properties of coatings deposited by different methods of high velocity spray process. An influence of sub-microcrystalline additions on basic mechanical properties of coatings was analyzed. Deposited coatings were characterized. Theirs overall quality, porosity, adhesion of coatings to substrate and theirs tendency to making cracks were analyzed.

Financial support of Structural Funds in the Operational Program - Innovative Economy (IE OP) financed from the European Regional Development Fund - Project No POIG.0101.02-00-015/09 is gratefully acknowledge.

The study of the growth kinetics of boride layers is an important tool to determine the suitable process parameters for obtaining an adequate boride layer thickness. In this study, the mathematical model of the growth kinetics of the layers on steels substrates was proposed for powder-pack boriding treatment. The boriding of the steels substrates was developed at temperatures of 1123 and 1223 K with exposure times of 2 and 8 h respectively. The tribological characterization was performed to determine the effect of the set of experimental parameters of the boriding process. The sliding wear tests were performed using a reciprocating wear test machine. All tests were conducted in dry conditions with a room temperature between 293 K and 296 K and 45% to 50% relative humidity. A velocity of 10 Hz and 15 mm sliding distance were used. The applied Hertzian pressure was 2.01 GPa. Optical microscopy and scanning electron microscopy (SEM) were used to observe and analyze the wear mechanisms. Additionally, the variation of the friction coefficient versus the number of cycles was obtained. It was possible to know the wear life of the Fe₂B layers and possible causes of its variation.

Although it is a well known fact meanwhile, that a standard Rockwell test or high-load Vickers test does not give any relevant information about thin films, dimensioning indentation or scratch tests for such surface structures is still difficult – if not impossible for more complex structures (e.g. multi-layer, graded, or nano-structured coatings). Hence, well-dimensioned indentation or scratch experiments are quite uncommon. As a result, indenter tips break away on, for instance, hard coatings rather often or measurement results do not correlate with practical experience.

Indentation measurements, scratch tests and tribology experiments should be well dimensioned in order to prevent such damage to measurement equipment, learn as much as possible about a coating (e.g. elastic modulus, yield strength, hardness, tensile strength, …), and reproduce the failure happening in a certain quality assurance test or even in real life.

Even though the basic principle has been outlined yet [1], the procedure of dimensioning such mechanic contact test is still quite difficult. Therefore, an quick and easy method to dimension indentation and scratch tests for thin films with respect to maximum normal force, indenter tip type, radius, and tip rounding will be shown in this work. This method, which is based on the „Oliver & Pharr method extended for coatings“ [2], is even accessible on the Internet enabling one to do the dimensioning virtually anywhere within just 2 minutes.

[1] N. Schwarzer et al., Surf. Coat. Tech., 206 (2011) 1327-1335.

[2] N. Schwarzer, J. Phys. D: Appl. Phys., 37 (2004) 2761-2772.

Acknowledgement: This study is financially supported by the Smart Coating Steel Development Center, WPM (World Premier Materials) Program of the Korea Ministry of Knowledge Economy.

Nanolayered AlTiN/TiN hard coatings are known to have superior performance in protection of surfaces at hard working conditions due to their properties such as low thermal conductivity, high wear resistance and high oxidation resistance. In the present study, scratch and wear behavior of nl-AlTiN/TiN nanolayer coating was investigated. The coatings were deposited on AISI D2, AISI H11, K600 and cemented carbide substrates by CC800/9 sinOx ML (CemeCon) industrial magnetron sputtering system. CSM Revetest scratch tester was utilized for the adhesion measurements. The scratch tests were performed under progressive load. The adhesive strength of the coatings was measured by microscopic observation, acoustic emission detection and friction force recording. Surface failures were analyzed by using optical microscope. Wear tests were performed on CSM tribotester using alumina balls at low and high sliding speeds, and friction coefficient and wear rate data were recorded. Wear traces were investigated by scanning electron microscope. It was found that the highest value of the critical load is obtained in the nl-AlTiN/TiN coating on cemented carbide substrate, and it is much higher than that of single layer TiN and TiAlN coating. Spalling, chipping, conformal cracking and tensile cracking are the failures of the nanolayered coating. Although wear rate of nl-AlTiN/TiN coating is higher than that of TiN coating at low sliding speed, its wear rate decreases with the increasing sliding speed and becomes lower.

MoS₂ coatings is effectively used in vacuum and in water vapor-free environments because of increased friction coefficient and decrased service life in room temperature. To increase friction and wear resistance of MoS₂ coatings are used different alloys elements (e.g., Ti, Nb, Cr) and materails (e.g., TiN, TiB₂). Therefore, in this study Ti/TiB₂/MoS₂ graded-composite coatings (GCC) were deposited by the closed-field unbalanced magnetron sputtering (CFUBMS). The structural properties of the coatings were analyzed by scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS) and X-ray diffraction (XRD). The hardness of the coatings was measured using a microhardness tester. The tribological properties of coatings were determined in room temperature (RT) and vacuum atmosphere. Ti/TiB₂/MoS₂ (GCC) have MoS₂ (002) and TiB₂ (100) reflections. The coatings exhibited a dense and non-columnar structure. Tribological properties of coatings in RT and vacuum atmosphere significantly affected from hardness,thickness and stoichiometric ratio of elements in the structure .

Key Words: Friction,Wear, Ti/TiB₂/MoS₂, graded-composite, CFUBMS

Austenitic stainless steels exhibit excellent corrosion resistance, but relatively poor wear resistance. Preceding studies of sequentially plasma carburized and nitrided AISI 316 steel [1] indicated an increase of wear resistance without a deterioration of corrosion resistance. As it is known that mechanical treatment prior to nitriding can lead to significant increase in the thickness of the nitrided layer [2], in this work we have investigated the effect of shot peening on sequential plasma processed AISI 316L.The sequential plasma treatment, which was performed at temperatures of 673K and 748K, consisted of a 2h carburization step followed by nitriding for 2h.

The structure of the evolved surface layers was analyzed by X-ray diffraction (XRD), scanning electron microscopy (SEM) and nanoindentation and was correlated with the wear behavior. XRD patterns of plasma-processed specimens indicated the presence of two distinct surface layers with expanded austenitic structure, one rich in nitrogen and another rich in carbon. In addition, some chromium nitrides were found for the specimen processed at 748K. SEM micrographs showed that the nitride layer is thinner than the carburized layer. The thinner nitride layer might be explained by the trapping of nitrogen due to the chemical binding with chromium [3]. The nanoindentation hardness profiles demonstrated three regions of hardness: the first one correlated with the nitrided layer, the second with the carburized layer and the third one with the substrate material. Higher hardness values were found for the nitrided layer formed at 673K, probably due to a higher concentration of nitrogen in solid solution, since chromium nitrides are present only in the sample nitrided at 748K. Relative to an untreated sample, the pre-shot peening had decreased the nanoindentation hardness in the nitrided layer, but not in the carburized layer. The curves of coefficient of friction also indicated regions of distinct behavior. The shot peening process smoothed the coefficient of friction curves on dry sliding wear test. The worn volume, evaluated by 3-D profilometry, showed that sequential plasma treatment at 748K after pre-shot peening leads to the best wear resistance.

[1] Tsujikawa Surf. Coat. Technol. 193 (2005) 309-313

[2] Shen Surf. Coat. Technol. 204 (2010) 3222–3227

[3] Moskalioviene Surf. & Coat. Technol. 205 (2011) 3301-3306

Transition metal dichalcogenides (TMD) are suitable as solid lubricants due to their anisotropic layered structure, where the adjacent lamellae with strong covalent bonding interact through relatively weak van der Waals forces. Pure sputtered TMD films are sensitive to environmental attacks, which limits their mechanical properties and wear resistance. Alloying of TMD with other element could improve their properties, such as adhesion, hardness and load bearing capacity. Recently, we have deposited amorphous W-S-N coating showing ultra-low friction during sliding in dry nitrogen (lower than 0.003). TEM analysis of the tribolayer adhered on the ball revealed tungsten oxide combined with tungsten disulphide; this observation was confirmed by XPS and Auger electron spectroscopy (AES). Thus, we decided to deposit this film with wide range of composition and tests its tribological properties in various atmospheres including humid air.

In present study the tribological behavior of W-S-N coating with different nitrogen content is sputtered from WS2 target in Ar/N₂ atmosphere. Besides the usual physical, chemical and mechanical characterization, including the evaluation of the chemical composition by electron probe microanalysis, the structure by X-Ray diffraction (XRD), the chemical bonding by X-Ray photoelectron spectroscopy (XPS), the morphology by Scanning electron microscopy (SEM), the hardness and the cohesion/adhesion, special attention was paid to the friction and wear behaviour in dry nitrogen.

The nitrogen content varied from 8 to 25 at.%, the hardness increased with nitrogen content from 5 GPa to 10 GPa. XRD spectra showed broad peaks typical of nanocrystalline WS₂. The friction was quite low even in humid air; the values were typically 0.2 to 0.3 in humid air. Investigation of the wear track and the ball wear scars by electron microscopies and by Raman spectroscopy shed light on the formation of low-friction tribolayer on the worn surfaces.

For manufacturing mechanical components in tribological contact it is often useful to employ liquid lubricants to increase the performance and reduce degradation of the interacting materials. However, unforeseen challenges can arise when the conventional boundaries are exceeded and components are exposed to extremes of environmental condition; significant variations in the temperature, pressure, and/or chemical media present can all act to drastically affect the behaviour of the materials or lubricants involved. For some of these applications a possible solution could lie with the optimisation of amorphous carbon film systems.

Potential attractive properties of amorphous carbon films include high hardness, low friction, chemical inertness, and self-lubrication. Such characteristics are useful in situations where low friction conditions are required, but lubrication retention is low (or corrosive media lead to changes in material properties in the tribological contact). In this work we explored the architecture, dopants and properties in a variety of commercially available amorphous carbon coating systems to assess how the material properties and adhesion evolve in-situ. Evaluation of films in actual operating conditions indicated their suitability for wear at elevated temperatures and/ or corrosion, thereby allowing new amorphous carbon coating formulations to be designed to resist these challenging environments more effectively.

In order to successfully characterise these thin amorphous carbon films we subjected samples to simulated environmental conditions to provide experimental data that supports the theoretical optimal compositions. For amorphous carbon we conducted these experiments alongside specific characterisation techniques, performed before and after (and, if possible during) environmental exposure. These techniques include scanning electron microscopy (SEM), Raman, and surface profilometry to determine the thickness and structure of the film, nano-indentation to determine changes in hardness, mechanical wear testing to measure tribological performance, and methods to determine the hydrogen content of the film like elastic recoil detection analysis (ERDA).

In this study we investigate the influence of different plasma treatments on the wear resistance of AISI 316L austenitic stainless steel. The chosen plasma treatments include carburizing at 475°C for 3 hours, nitriding at 450°C for 5 hours, and a sequential process composed of carburizing at 475°C for 3 hours followed by nitriding at 450°C for 5 hours. In order to correlate wear behavior and structure as well as the concentration of carbon and nitrogen at the surface, the plasma treated samples were thoroughly investigated by means of scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), X-ray diffraction (XRD), glow discharge optical emission spectroscopy (GDOES), ball-on-disc dry sliding wear tests, micro- and nanoindentation.

Each plasma treatment led to a modified surface layer of the AISI 316L steel. It was shown that these surface layers had different thicknesses for each of the three different treatments and two expanded austenitic structures without precipitates. Post the initial running-in period of the sliding wear tests, sharp transitions were observed, probably due to the plasma modified surface layers. After identifying the sliding distances corresponding to these transitions, the tests were stopped at these points and EDS compositional maps of the wear tracks were taken. The depth of wear tracks and the worn volumes were measured by 3D profilometry. The significant drops in carbon and/or nitrogen concentrations of each wear track indicate that the modified layers were almost worn out at these positions. Comparing the worn volumes, the sequentially plasma treated sample showed the best wear resistance. For this system three defined regimes were identified: the first probably correlated with the upper nitrided layer, the second with the carburized layer and finally the third one with the substrate. Micro- and nano hardness measurements demonstrated that the wear behavior can be related to the different mechanical properties of these three different layers.

This study shows that the wear behavior is strongly related to the particular structure of the modified surface. A steady-state wear will be only observed for long sliding distances, when the worn material already corresponds to substrate bulk material.

VN-Cu and MoCu-N nano-composite coatings were prepared using a reactive magnetron sputtering technique. A pure vanadium or molybdenum target was sputtered using a HIPMS power supply and the copper doping was made using a copper target attached to a DC power supply. Along with argon, nitrogen gas is used as a reactive gas during the deposition. HIPIMS was also used for metal ion etching on the steel substrate in order to improve the adhesion of the coatings. The films are grown on 440C stainless steel flat and 3/8” diameter ball samples for tribological tests and Si wafer samples are coated for other coating characterization studies. The microstructural properties are studied using thin film X-ray diffraction; the compositions of the films before and after tribological tests are evaluated by using X-ray photoelectron spectroscopy (XPS). The mechanical properties of composite coatings were assessed using a nanoindentation technique.

The tribological tests were conducted using a high temperature ball on disk system in open air environment. The samples were tested at room temperature, 350°C and 650°C. The results show that the coefficient of friction (COF) has a strong dependence on test temperature. For both VN-Cu and MoN-Cu coatings, COFdecreased with increasing temperature and the lowest COF (i.e., 0.4) was attained at 650C due to the formation of the lubricious metallic oxides on sliding surfaces. The wear resistance of coatings also improved with increasing temperature. The nature of lubricious oxides is studied using Raman and x-ray photoelectron spectroscopy techniques and correlated with the friction and wear performance of coated surfaces.

During the last years the instrumented indentation test has been established as a common analysing technique for the material characterisation. Beside the hardness value these technique provides further important material properties. In the recent years the thickness of new developed industrial coatings decreased constantly. Due to the high force resolution and the ability to apply very low loads, the instrumented indentation test also offers the possibility to measure such thin coatings without an influence from the substrate.

For different reasons coatings are getting thinner recently. A coatings thickness well below one micrometer is standard and coatings in the order of 100 nanometers are nothing unusual, depending on the application. Hard coatings like PVD or DLC are also following the trend. But those coatings often tend to have an uneven surface with roughness values in the order of the coating thickness. The combination of a small coating thickness and a high roughness is a challenge to the instrument and the user.

The poster shows different ways to analyse such samples. Sometimes an increased number of measurements allow comparing the mean values of different samples. Measuring a cross section of the sample can also improve the results. A high precision of the XY-positioning is mandatory for this. Using an AFM can give additional information about the sample which is not available by standard nanoindentation measurements.

During designing and manufacturing machinery and equipment (e.g. components for automotive or food and medicine industry), one of the development directions is substituting and eliminating liquid lubricant by solid lubricant. The solid lubricant predominantly are built into a surface of construction materials working in friction conditions. An application of solid lubricant constituting integral part of structure leads to decrease of frictional resistance and wear of couple of friction. Reliable long-term cooperation while maintaining the desired efficiency can be obtained by applying less quantity of liquid lubricant.

This paper presents a method of production metal matrix composites with aluminum oxide foam covered by glassy carbon used as a reinforcement. The glassy carbon surface was formed for decreasing of friction coefficient and reduction the wear. The glassy carbon acts as solid lubricant in this case. In first step of technology liquid glassy carbon precursor is deposited on ceramic foam, subsequently cured and carbonated at elevated temperature. In this way ceramic foam is covered glassy carbon coating with 2 ÷ 8 µm of thickness. It provides desirable amount of glassy carbon in the structure of the material. In the next step, porous shapes with carbon coating are infiltrated by liquid matrix of Al-Si-Cu alloy. Thereby, equable distribution of glassy carbon in composite volume is achieved. Moreover, typical problems for composites reinforced by particles like sedimentation, agglomeration and clustering of particles are avoided. Tribological characteristics in friction in air conditions with cast iron as a counterpart were made. Produced composites with glassy carbon layer are characterised by friction coefficient between 0.08 ÷ 0.15, thus meeting the typical conditions for solid lubricants.

Nanostructured materials have attracted many researchers due to their outstanding mechanical and physical properties. For example, carbon nanotubes (CNTs) or carbon nanofibres (CNFs) are considered to be attractive reinforcement materials for light weight and high strength metal matrix composites. The inclusion of a reinforcement phase into electrodeposited coatings to form a composite has been shown to be useful for many tribologically aggressive applications. Composite coatings containing solid particles of carbides, oxides, diamonds, and polymers are rapidly increasing in importance in modern engineering application due to their enhanced hardness, wear resistance, self-lubrication and corrosion resistance when compared to metal or alloy. The improved properties of composites coatings heavily depend on the nature and content of particles in the coatings.

In the present work, Nickel /multiwalled carbon nanotube (MWCNT) metal matrix composite coatings were deposited by pulse electro co-deposition method from a Watt's type electrolyte. The influence of the MWCNT content in the electrolyte and peak current density on the particle co-deposition and distribution, the surface morphology, microstructure, microhardness, tribological features and corrosion resistance of nanocomposite coatings were studied. Copper substrates were used for electro co-deposition of Ni matrix/MWCNTs with the diameter of 50–60 nm and length of 10 mm carbon nanotube reinforcements. The electrodeposited Ni matrix coatings were characterized by scanning electron microscopy (SEM) and X-ray diffraction (XRD) analysis and Raman spectroscopy. The tribological behaviors of the electro co-deposited Ni/MWCNT nanocomposite coatings sliding against an M50 steel ball (Ø 10 mm) were examined on a tribometer. All the friction and wear tests were performed without lubrication at room temperature and in the ambient air (with a relative humidity of 55–65 %). A comprehensive worn surface analysis was performed using SEM, XRD, Raman and 3D surface profilometer facilities. Corrosion tests were performed in aqueous NaCl (3.5 wt.%) using electrochemical measurements for pure nickel coating and Ni/MWCNTs composite coating.

Sliding electrical contacts are commonly used, and the contact material should maintain stable properties over the course of several thousand cycles. Most electrical contacts are coated with noble metals to prevent formation of insulating metal oxides, although in tribological systems such coatings wear down and shorten the lifetime of the product. It is also known that e.g. Ag coatings suffer from tarnishing. Transition metal carbide/carbon nanocomposite films, with carbide grains embedded in an amorphous carbon matrix, have been suggested as alternative to noble metals. The carbide phase provides high conductivity, high corrosion resistance, and high hardness, while the carbon matrix improves wear properties and reduces friction.

We demonstrate use of chromium carbide glass-like films in a rocking motion sliding electrical contact setup, capable of in situ contact resistance measurement and life time simulation. Amorphous Cr-C-H films were grown by reactive direct current and high power impulse magnetron sputtering from a Cr target. An industrial scale PVD system allowed for growth rates from 0.1 to 0.5 µm·min^-1. Film structure and properties were studied by XPS, Raman spectroscopy, XRD, TEM, SEM, nanoindentation, unlubricated reciprocating sliding experiments, and by the novel sliding electrical contact setup. The films were relatively soft for being carbide-based, with hardness values of 8 - 12 GPa, which can be explained by the amorphous structure. Coefficients of frictions vs. steel bearing balls were µ = 0.13 – 0.60, correlated to the fraction of amorphous carbon. Films grown on SS316L were tested as sliding electrical contacts, and major differences in useable life time as electrical contact were observed depending on the chemical bonds present in the films. The best films demonstrated performance comparable to industry standard Ag for up to 10 000 cycles.

Reliability and availability of mechanical components at operational stage is reduced due to tribologial failures. In order to reduce tribological failures due to wear, application of hard coatings on mechanical components is considered one of the most appropriate and feasible alternative. In this research study, mechanical and tribological behaviour of ZrN coatings deposited on titanium modified austenitic stainless steel (alloy D- 9) substrates has been investigated. The coatings were deposited in the deposition temperature range 300–873 K, using the pulsed magnetron sputtering technique. Scratch adhesion tests were carried out using Rock well indenter under various conditions of load. Hardness of these coatings were determined using Vicker indenter. Detailed tribological studies were conducted to understand the friction and wear behaviour of these coatings under various conditions of load and sliding velocity. For all tribological studies steel and ceramic balls were used as counter face material. 3D-Surface profiles of all wear tracks was carried out using 3D universal profiler.

Surafce profiles indicated propagation of Hertz cracks leading to brittle fracture of ZrN coatings. Higher coeffcient of friction was observed in case of ceramic ball against ZrN coated disc, as coampared to steel ball against ZrN coated disc. However, a lower value of coefficent of frction was observed in case of coatings deposited at higher tempearture. Wear increases with the increase in normal laod. The failure of coatings, variation in the coefficient of friction and wear with the steel and ceramic balls is further discussed in relation with morphology and elemental distribution in the wear tracks of the ZrN coatings.

The pumps of electro-hydrostatic actuators are frequently subject to boundary lubrication, since they operate as a control element compensating for position control errors. Therefore, their tribological performance should be capable of enduring the extreme conditions to which they are subject to compared to conventional pumps operating constantly at high speeds. When conventional swash plate type piston pumps are applied to electro-hydrostatic actuators, their performance under boundary lubrication conditions should be examined and supplemented. The frictional power losses, as well as the wear rate of the sliding components such as piston shoes, can significantly increase under boundary lubrication conditions. In this paper, a DLC-coating was applied to the swash plate and ball joint of pistons, and its ability to reduce the power losses from the frictional solid-to-solid contact and the leakage flow rate of the hydrostatic piston shoe bearing was investigated. The DLC-coated swash plate was able to effectively reduce the friction force on the piston shoe, while the leakage flow rate could also be reduced using the DLC-coated ball joint. Using the DLC-coated ball joint and swash plate together the total power loss from the hydrostatic piston shoe bearing could be reduced by more than 40% in the pump speed range from 10rpm to 100rpm

Acknowledgement

The authors would like to acknowledge the support from National Research Foundation of Korea (NRF) grant funded by the Korea Government (MEST) (NRF 2011-0015640)

Tribological behaviour of bearing surface of extrusion dies has an important technological and economic importance since it affects the tolerance and surface quality of extrudate and increases manufacturing cost and determines the service life of dies. Extrusion dies are usually made from hot work tool steels such as AISI H13. In order to increase the service life, they are always surface treated by various forms of nitriding. Surface-coating by physical vapour deposition (PVD) or chemical vapour deposition (CVD) is currently being introduced as a means to further improve the wear resistance.

In this study, TiAlCrNbN nanocomposite thin films were deposited on AISI H13 steel substrate by Pulsed Dc Closed Field Unbalanced Magnetron Sputtering, and the effect of frequency, bias voltage and working pressure on the mechanical and tribological properties were investigated. The coatings have been characterized by X-ray diffraction, scanning electron microscopy and energy dispersive spectroscopy. The lowest amount of wear were attained at lowest frequency and highest bias voltage and working pressure.