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JUNE 28 WEDNESDAY MORNING JS2-WeM-OR.2 WEAR RESISTANCE OF TITANIUM-ALUMI-NIUM-CHRO- MIUM-NITRIDE NANOCOMPOSITE THIN FILMS. A. Alberdi, M. Marín, B. Díaz. Fundación Tekniker. Avda. Otaola, 20. 20600 Eibar (Spain). O. Sánchez. Institute of Materials Science (ICMM). Cantoblanco, 28049 Madrid (Spain) Titanium nitride, titanium-aluminium nitride and chromium nitride are now used widely in manufacturing industry to protect cutting and forming tools against wear. TiN was the first PVD ceramic coating to be used successfully to machine steel in industry and it is still the most recognized. TiN is a wear resistant coating suitable for a wide range of applications. It is used for machining carbon stainless steels, cast irons and aluminium alloys, protecting dies, moulds and a range of metal stamping and forming tools. However, TiN has now been superseded in many applications by TiAlN, which offers superior performance for a range of metal machining and fabrication applications. It has been pointed out that the reason for this better performance is the formation of aluminium oxide on the surface, which increases its operational temperature range. Although CrN is softer than TiN, CrN is a tough ceramic coating with good oxidation resistance. Presently, CrN is the PVD hard coating recommended for most metal forming applications. Advanced PVD coatings based on TiAlN are being developed recently, which possess enhanced high temperature oxidation and wear resistance. Typical strategy to enlarge the temperature range of TiAlN is the addition of metals able to generate high resistant oxides, like chromium, molybdenum, yttrium or vanadium. In this way, authors have developed novel TiAlCrN multilayered nanocomposite thin films, which alternate CrN and TiAlN individual 10-12 nm thickness layers up to a total thickness of 1-3 μm. These coatings were grown on WC-Co inserts and high speed steel samples by simultaneous arc evaporation of pure Cr and Ti-Al alloy targets. Wear resistance of these coatings was studied through high temperature pin-on-disk experiments. Results demonstrated that this kind of coating structures improved several times the wear resistance at high temperature of commercially available TiAlN coatings. Key words: TiAlCrN ceramic coatings, physical vapour deposition, high temperature wear resistance. 100
JUNE 28 WEDNESDAY MORNING JS2-WeM-OR.1 TRIBOLOGICAL PROPERTIES OF SILICON NITRIDE CERAMICS COATED WITH DLC AND DLC-Si AGAINST 316L STAINLESS STEEL J. R. Gomes. Departamento de Engenharia Mecânica, CIICS, Universidade do Minho, 4800-058 Guimarães, Portugal. J. M. Carrapichano. Departamento de Engenharia Mecânica, Instituto Superior de Engenharia de Coimbra, 3040-228 Coimbra, Portugal. S. S. Camargo Jr., R. A. Simão, C. A. Achete. Departamento de Engenharia Metalúrgica e de Materiais, Universidade Federal do Rio de Janeiro, Cx. Postal 68505, 21945-970 Rio de Janeiro, RJ, Brazil. R. F. Silva. Departamento de Engenharia Cerâmica e do Vidro, CICECO, Universidade de Aveiro, 3810-193 Aveiro, Portugal. Diamond-like carbon (DLC) is an adequate coating on a large variety of materials for tribological purposes. Its intrinsic hardness, smoothness and solid lubricious capability are key properties that afford an outstanding combination of low friction coefficient and high wear resistance. However, the performance of a tribosystem is also determined by the type of counterface material, the environmental conditions and the presence or not of interfacial media. For example, in the automotive parts industry, the valve guides or the transmission gears are today coated with DLC. Another practical example of contacts that may involve steel as the mating material of DLC are forming tools to manufacture steel products. Plasma enhanced chemical vapour deposition (PECVD) of DLC-Si or pure DLC coatings were performed, respectively, by conventional rf glow discharge from gaseous mixtures of methane and silane or taking only pure methane. In this work, an engineering ceramic, silicon nitride (Si 3 N 4 ), is used as DLC substrate aiming the minimization of adhesion problems, usually found when some metallic substrates are employed. The ceramic substrates were placed onto the cathode of the deposition system where the rf power was applied achieving self-bias voltages varying from -200 to -800 V. The tribological properties were assessed by pin (316L stainless steel)-on-disc (Si 3 N 4 ) experiments, without lubricant, at room temperature, under ambient air and 50-60% relative humidity. The normal applied load assumed the values of 10 N and 20 N. The sliding speeds varied from 0.2 m/s to 1.0 m/s. The characterisation of the disc and pin worn surfaces was carried out by scanning electron microscopy provided with energy dispersive X-ray spectrometry (SEM/EDS) and atomic force microscopy (AFM). A first set of experiments was carried out in order to compare the tribological behaviour of DLC-Si and pure DLC coatings on Si 3 N 4 . An early partial delamination of the DLC-Si coatings was observed, although leading to a steady-state friction regime with friction coefficients around 0.14, a low value in unlubricated conditions. This favourable frictional response is due to the wear-induced surface graphitisation and to the role of self-lubricating layers of adhered debris in both the sliding surfaces. The stainless steel contact surface was extensively covered by a Si, C and O rich tribolayer, promoting a third-body protection to the steel pin. An improved tribological response was obtained with pure DLC coated Si 3 N 4 discs sliding against the stainless steel pins. This system almost instantaneously attains the steady-state friction regime, keeping the DLC film integrity, contrarily to the DLC-Si damaging, which leads to noisy friction curves coming from cyclic frictional events. The preservation of the coating demonstrates an adequate adhesion for tribological purposes up to 20 N of applied load. The wear coefficient of the pure DLC coated Si 3 N 4 disc was, at least, one order of magnitude lower than that of the DLC-Si coated one, always below 10 -6 mm 3 N - 1 m -1 . The set of tribological experiments of pure DLC coatings obtained under distinct self-bias application during the PECVD process revealed that the wear coefficient values obtained for the –200V biased coating are slightly better than those presented by the –800V biased one. However, with respect to the friction coefficient values, a trend to lower values occurs for the –800V biased films. Additionally, the typical friction pattern for low biased grown coating is much more unstable than the very smooth one of the –800V biased film. 99
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Sigilum Universitatis Studii Salama
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