ICMCTF2010 Session GP: Symposium G Poster Session

The piston ring contact in a typical automotive engine is an example of a highly loaded. Therefore, for piston ring design several aspects are important. Among them are function, cost, NVH, fuel economy, durability, and impact on other design aspects of the engine.

Continuously contacting with piston ring, the face of cylinder liner, brings about abnormal wear such as unfairwear or earlywear. because the engine get more powered and one requirement for a good fuel economy is to achieve a low level of mechanical friction.

In this study, modern low friction coatings at the piston ring interface aimed to investigate the potential. The coated specimens for piston ring wear test were producted by using PVD coating (WC/C, CrN+ WC/C, CrN +DLC). The profile of coated specimens were observed by non-contact type optical surface measuring system and the friction-wear behaviors of coated specimens were investigated by using piston ring wear tester. Piston ring wear test was performed to analyze the friction and wear behavior. The results showed that the application of low friction coatings effectively improved tribological performance of the piston ring .

Toward high qualification of oxide glass molding, reduction of separation temperature and adhesive stress of mold material from deforming glasses is keenly noticed as a challenging issue in technology. Geometric inaccuracy or unacceptable deviation in tolerance significantly increases with increasing the separation temperature. Even in using CrN coating, adhesive stress exceeds 1 MPa during the molding process.

Our developing nano-columnar amorphous carbon coating is applied to this oxide-glass molding die to solve this mold-glass mechanical interaction. This nano-columnar coating has vertical aligned nano-structure in the direction of thickness with higher density inter-columnar region; this coating deforms elastically up to 8 to 10 % of film thickness via nano-indentation test. Atomic force microscopy, Raman spectroscopy and high resolution TEM reveal that this coating is composed of two phase composite where amorphous carbon column is covered by graphitic inter-granular regions. Owing to distributed elastic modulus, this coating can afford to retard the onset of mold-die separation from deforming glasses and to reduce the adhesive stress. In addition, thermal stability of this coating is enhance by optimization of interlayer between nano-columnar layer and die surface.

The isothermal molding stamping is utilized to evaluate the engineering durability of this nano-columnar coated WC/(Co) die in molding the meniscus oxide glass lens. The holding temperature is controlled to be just below the glass transition temperature (Tg). Two types of oxide glasses with Tg = 673 and 773 K are employed to investigate the effect of temperature transients on the molding behavior. In both cases, geometric deviation of molded glass lens is much reduced owing to this elastically deforming nano-columnar coating.

Plasma immersion ion implantation (PIII) into the inner surface of a cylindrical pipe has been investigated and demonstrated the larger difficulties especially for small diameter tubes. A new technology is proposed for the inner surface treatment in our lab. In this novel technique, an inductively coupled radio-frequency coil is utilized as internal plasma source. The coil also acts as a grounded electrode to eliminate the overlapping effect of plasma sheath in the tube to increase the bombardment energy of incident ions. The influence of gas pressure, RF power and geometry of the helical inductive coupler on the plasma distribution in tubes has been investigated. Wear resistance and corrosion resistance of the inner surface modified by nitrogen ion implantation have also been studied. The experimental results indicate that steady discharge is sustained with uniform plasma density in the interior of the pipe based on this new technique. The plasma density increases with increasing RF power and the best uniformity has been achieved with RF coil turns of 35 and RF power of 250W for the tube 200mm in length and 30mm in diameter. The wear resistance and corrosion resistance of the internal surface have been enhanced significantly by plasma immersion ion implantation. The experimental results demonstrate the feasibility and superiority of this new method for ion implantation into inner surface of a cylindrical pipe with a small diameter.

Coated and nanostructured surfaces gain much importance for improving the efficiency of high temperature applications (e.g. in turbines). By embedding ceramic particles with a negative thermal expansion coefficient (NTEC) into a metallic matrix, a reversible thermal activation of a nanostructured surface can be established. At high temperatures a defined drag reducing surface microstructure (“shark-skin”) is formed in the the coating surface, while a self-cleaning effect at low temperatures (in idle period) is achieved by the reversal of the deformation. A feedstock powder produced by high energy ball milling and consisting of nanocrystalline yttrium oxide and tungsten oxide particles embedded into a conventional MCrAlY alloy was used for the investigations. By using different thermal spray and cladding techniques the powder is deposited onto different substrates. In a next step the coating is implanted with oxygen, yttrium, or xenon to induce the formation of Y₂W₃O₁₂ particles inside the coating in the desired morphology. Y₂W₃O₁₂ is a ceramic with a strong negative thermal expansion coefficient and is stable also at temperatures above 1373 K. The effects on phase formation and morphology changes are analyzed in detail. Results of phase formation, surface micro-morphology, microstructure and properties of these high-temperature coatings are presented.

The work is supported by the German Research Foundation (DFG) within Priority Programme 1299 (HAUT).

Within the first process, lanthanum cuprate films were deposited by co-sputtering of metallic copper and lanthanum targets in various Ar-O₂ reactive mixtures. The oxygen flow rate introduced into the deposition chamber was optimised to fully oxidise the sputtered atoms. The atomic ratio La/Cu in the film was adjusted by the variation of the pulsed DC current applied to the copper target. Within this process, the experimental window range for successful La₂CuO_4+δ deposition was found to be very narrow. The second process, namely, reactive sputtering of a composite La-Cu target, shows easier control on the film composition. The La/Cu atomic ratio is strongly dependent to that of the composite target. In the third process, lanthanum and copper oxide multilayers have been synthesized by reactive sputtering. The La/Cu atomic ratio was controlled by the thickness of each layer

Whatever the deposition process, an annealing step in air at 600 °C was necessary to obtain the crystalline La₂CuO₄ phase. Finally, the influence of the substrate nature (silicon, SrTiO₃, fused silica, stainless steel) on the film properties was investigated.

This paper deals with the effects of Cu²⁺cations on structure and mechanical properties of Plasma Electrolytic Oxidation (PEO) coatings on Al. The coatings were prepared on BS Al-6082 aluminium alloy using the pulsed bipolar PEO mode in silicate-alkaline electrolyte with addition of 0 to6 g/l of copper acetate Cu(CH₃COO)₂. In order to investigate the coating morphology, chemical and phase composition, SEM observations EDX and XRD analyses were carried out. Residual stresses have also been studied using the XRD sin²ψ method. The mechanical behavior was investigated using nanoindentation, scratch and impacts tests.

It was found that the addition of copper acetate increases the proportion of α-Al₂O₃ at the expense of γ-Al₂O₃ constituent. Cross-sectional SEM studies and EDX analysis revealed that copper tends to segregate in the outer porous region of the coating. Residual stresses and Young's modulus as well as alpha phase proportion do not follow a uniform trend on copper concentration. With addition of 1g/l of copper acetate, a slight decrease in these characteristics is observed but for the coating formed with 2g/l of copper, they are enhanced to finally suffer a significant drop at 6 g/l.

Mechanical tests indicated that incorporation of copper has direct effect on the coating resistance to impact wear and its adhesion to the substrate; these both decrease with the increase of copper content in the coating. On the contrary, the coating hardness increases with Cu concentration. In conclusion, the optimum combination of structural and mechanical characteristics of the coatings was found at an addition of 2g/l of copper acetate to the base electrolyte.

Significant damages occur to the forming molds and stamping molds when ultra high-tensile steel sheets is implemented in the production process. To improve the lifetime of such stamping molds, conventional thermal diffusion processes to form carbide materials such as VC, NbC or TiC [1] have been used. While these carbide diffusion coatings show relatively good wear resistance at moderate stamping condition, their durability is not satisfactory for stamping of ultra high-tensile steel at minimum lubrication condition. Another drawback of such diffusion processes is their treatment temperature, which is usually close to 1000ºC. Conventional cold working die steel, such as D2, are tend to be thermally distorted by such high temperature treatment resulting in a size deviation of the final stamped products.

A novel nitiride based multilayer coating (BELCOAT-SS[2]) was deposited by AIP process on the conventional D2 steel. Deposition temperature is less than 450ºC, which is significantly lower than conventional diffusion carbide forming process and almost no dimentional change was observed by the coating process. Primarily, coatings basic properties such as hardness and adhesion were compared with conventional carbide diffusion coatings. Hardness of the BELCOAT-SS is approximately 32 to 35 GPa, whereas 35 GPa is measured for the VC and TiC.

Adhesion was evaluated by scratching the coated surface by using spherical diamond indenter with progressive load up to 100 N. Film cracking was observed at around 20 to 30 N in the case of carbide coating and no film cracking was observed up to 50 N in the case of BELCOAT-SS.

In many engineering applications the selection of a coating is largely dependent on its physical and mechanical properties such as hardness, elastic modulus and adhesion to the substrate. In addition, the through thickness continuity and structural integrity of the coatings are of paramount importance, particularly in multi-layer coating structures. The aim of this paper is to establish and compare the physical and mechanical properties of five different coating structures through a comprehensive characterisation of mono- and multi-layered coatings produced by discontinuous duplex treatment processes (ion nitriding + PAPVD coatings).

In this work, various PAPVD coating structures [CrN, (Cr/CrN)x8, (CrN/TiN)x3, TiN, TiAlN] were deposited on an AISI H13 hot-work tool steel substrate after ion nitriding. The thickness of the individual component layers of the coatings was measured and microscopic observations were performed after the deposition process to assess continuity and integrity of the coatings. Nano indentations were performed in order to obtain the elastic modulus and the hardness of the coatings. Elemental through-thickness profiling concentrations within the coating structures were determined using Glow Discharge Optical Emission Spectroscopy (GDOES). Finally, coating adhesion was determined using the scratch test method. Changes in the acoustic emission and in the tangential force were recorded during the scratch tests to establish the progressive stages of failure of the coatings until complete removal. Scratch tests data was complemented by microscopic observations of the scratches at each failure stage.

Based on the analysis, it was concluded that the TiN and TiAlN coating systems exhibit comparatively higher hardness and Young’s modulus than the other PAPVD coating systems. In terms of adhesion, the Cr-based coatings produced higher levels among which CrN was highest. The results of this investigation may provide useful information for the selection of coating systems for an intended engineering application, based on coating’s properties.

This paper concerns the process of the composite: ‘nitrided layer-PAPVD coating’ creation on substrates CoCr alloy intended for biotribological applications. The irregularities and imperfections of the surfaces and the dynamic nature of human motion results in high stresses. The difference in modulus of elasticity between ceramic coating and biocompatible CoCr alloy substrate results higher susceptibility of coatings to fracture under cyclic loading and biotribology conditions. In order to diminish this effect and improve load carrying capacity of the system, the nitriding process was studied in this work.

Five nitriding processes with varying nitriding potential ( p(N⁺/H⁺) =1, 1.5, 2, 2.5 and 3) were selected for optimising. Modulus of elasticity and nanohardness of nitrided layers were measured by nanoindentation. Crossections were examined by means of scanning electron microscopy (SEM) in order to determine the thickness and the uniformity of the affected zone. The change in surface roughness was studied with the help of 3D roughness parameters obtained by atomic force microscopy (AFM). It was found that the most suitable properties of the surface layer were achieved by nitriding at p(N⁺/H⁺) =2.5.

According to this result, CrN as well as multilayer TiN/CrN coatings were deposited onto the substrates with and without nitiriding for evaluation of the nitriding effect on the adhesion. CoCr alloy nitrided were included for comparison. All these conditions were characterized by means of several analytical methods: AFM, nanohardness, SEM, X-ray diffraction (XRD), GDOES and scratch test.

The scratch test has revealed the improvement of adhesion of the PAPVD coatings due to nitriding of the CoCr alloy substrate.

The interest to the growth processes of anodic oxide films on valve metals, especially Al, Mg, Ti and Zr, has been recently revived due to rapid development of high-voltage plasma-assisted electrochemical surface treatments in alkaline electrolytes known as Plasma Electrolytic Oxidation (PEO). The films formed by this method possess superior protective properties and show many promises for functional applications. It is suggested that, unlike conventional anodising, formation of PEO coatings in alkaline electrolytes occurs via hydration of anodically dissolved metal ions followed by hydroxide precipitation, with subsequent dehydration and sintering by plasma discharge. Unfortunately, available electrochemical techniques are not accommodated for diagnostics of such processes.

In this study, the voltastatic method was adopted and applied for kinetic investigations of the growth processes of anodic oxide films on magnesium and aluminium. In alkaline solutions the current maximum is present on anodic voltastatic transients, which is characteristic of the processes controlled by the formation and growth of new phase nuclei. At the early stages of the coating formation process, the most probable mechanism takes into account an active metal dissolution with hydroxide formation in the near-to-the electrode electrolyte region. This is associated with 3-dimentional nucleation process during re-deposition of the dissolved metal hydroxide phases.