ICMCTF2008 Session E1-1: Friction and Wear of Coatings: Lubrication, Surface Effects and Modeling

Monday, April 28, 2008 10:00 AM in Room California

Monday Morning

Start	Invited?	Item
10:00 AM		E1-1-1 Influence of the Nitriding and TiAlN Coating Thickness on the Mechanical and Tribological Properties of Duplex Coating Systems on H13 Die Steel L. Suzuki (Neodent CO, Brazil); J. Lin, J.J. Moore (Colorado School of Mines); R. Torres (Catholic University of Parana, Brazil) H13 die steel substrates were gas nitrided using three different nitriding layer thicknesses of 30, 60 and 90 Ä. These nitrided samples were subsequently coated with TiAlN films using cathodic arc with two thicknesses of 3.5 and 8 µm. The three nitrided layers were initially characterized with respect to phase chemistry and hardness profiles. The gas nitriding process produced an outer compound layer on the surface of the H13 die steel and an inner diffusion zone with nitrides precipitates. The hardness profiles for each of these nitrided samples were quite similar. In the second part of this project TiAlN films were deposited on the nitrided samples to a thickness of 3.5 and 8 µm. Chemical analysis performed on these duplex coating systems using EDS revealed that the Ti:Al ratios in the TiAlN films were composed of 30 at.% aluminum and 70 at.% titanium. Nanohardness results revealed that coating hardness was influenced by the nitriding layer thickness; the thicker the nitriding layer the lower the coating hardness. The tribological behavior as determined using a pin on disk test showed a dramatic improvement in the wear behavior when the samples are covered with TiAlN.
10:20 AM		E1-1-2 Friction and Galling Properties of Coatings and Surface Treatments for Cold Forming Applications B. Podgornik, J. Vizintin (University of Ljubljana, Slovenia); S. Hogmark (Uppsala University, Sweden) Manufacturers of parts are confronted with ever-increasing demands on higher productivity, which put increased requirements on wear and fatigue resistance of the tools. Deposition of hard PVD and CVD coatings (i.e. TiN, TiAlN, CrN,...) has improved forming process in terms of load and has considerably enhanced tools wear resistance in numerous cases. However, in the case of sheet metal forming also resistance to galling, which determines product surface finish is a very important parameter. As shown by different studies, surface engineering of the tool surface can greatly improve forming tool galling properties, but which technique and coating to select will in a great extend depend on the work material to be formed. The aim of our research work was to investigate and compare different hard coatings and surface engineering techniques as to the tendency for work material adhesion and galling resistance when tested against different work materials. The surface coatings included were PVD deposited TiN, TiB₂, VN, TaC and DLC coatings. They were all applied to cold work tool steel and compared to surface engineering techniques like deep-cryogenic treatment, plasma nitriding and surface polishing. Tool steel samples were tested in the load-scanning test rig against the most demanding materials in terms of galling, including austenitic stainless steel, aluminium alloy and titanium alloy. Results were then evaluated in terms of coefficient of friction value and evolution, and critical load corresponding to the beginning of work material transfer, determined by post-test surface analysis.
10:40 AM	Invited	E1-1-3 Surface-Nano-Texturing by Aluminum-Induced Crystallization of Amorphous Silicon R. Premachandran Nair, H. Wang, M. Zou (University of Arkansas) Aluminum-induced crystallization (AIC) of amorphous silicon (a-Si) has been studied extensively to produce large continuous poly-Si grains for electronic and photovoltaic applications, such as thin-film transistors, sensors, solar cells, and display panels. This paper reports a novel use of AIC of a-Si technique for nano-scale surface-topography-engineering to improve surface tribological performances. Various nano-textured samples were first fabricated by using AIC of a-Si technique employing different a-Si thickness and annealing conditions. The surface topographies of these nano-textured surfaces were then characterized using scanning electron microscope and atomic force microscope. The effects of a-Si thickness and annealing conditions on the resulting nano-surface-topography were investigated. It was found that the size, height, and density of the nano-textures can be controlled by changing the a-Si thickness and annealing conditions. The adhesion and friction properties of the nano-textured surfaces were also studied and compared to a smooth Si surface. It was shown that nano-textured surfaces have significantly reduced adhesion and friction compared to the smooth surface. The nano-textured surface that had an optimum texture size and density showed the best frictional performance.
11:20 AM		E1-1-5 Abrasive Wear Resistance of Ti_1-xAl_xN Hard Coatings Deposited by a Vacuum Arc System with Lateral Rotating Cathodes X.Z. Ding, C.T. Bui, X.T. Zeng (Singapore Institute of Manufacturing Technology, Singapore) In this work, a series of Ti_1-XAl_XN (0≤x≤0.7) coatings were deposited on high speed steel (HSS) substrates by a vacuum arc reactive evaporation process from two lateral rotating elemental titanium and aluminium cathodes in a pure nitrogen atmosphere. The composition, crystalline structure and hardness of the as-deposited coatings were analyzed by energy dispersive X-ray spectroscopy (EDX), X-ray diffraction (XRD), and nanoindentation experiments. The abrasion wear resistance of the TiAlN coatings was measured by a micro-abrasion tester with the presence of SiC water-based slurry with a concentration of 0.35 g/cm³. It was found that with increasing the Al/Ti atomic ratio the hardness of the as-deposited TiAlN coatings initially increased up to a maximum value of about 40 GPa at around Al/Ti=1.2, and then the coating hardness decreased rapidly with increasing aluminium content further. The abrasion wear resistance of the TiAlN coatings is evidently better, with one order of magnitude lower in the wear rate, than the bare HSS substrate. With increasing Al/Ti atomic ratio, the variation trend of the abrasion wear rate of the TiAlN coatings is generally opposite to that of coating hardness. In other words, generally, the abrasion wear rate is inversely proportional to the coating hardness. That means the abrasion wear resistance of the TiAlN PVD hard coatings is predominately determined by the hardness of the coating materials. It was also noted that, for the coatings with similar micro hardness, the coating with higher aluminium content exhibits evident better abrasion wear resistance than the coating with lower aluminium content. This fact could be related to the finer microstructure of the coatings incorporated with higher aluminium content.
11:40 AM		E1-1-6 Arc Evaporated Ti-Al-Ta-N Coatings: the Effect of Bias Voltage and Ta on High-Temperature Tribological Properties M. Pfeiler (Materials Center Leoben Forschung GmbH, Austria); G.A. Fontalvo (University of Leoben, Austria); J. Wagner (Materials Center Leoben Forschung GmbH, Austria); K. Kutschej (University of Leoben, Austria); M. Penoy (Ceratizit Luxembourg S.á.r.l., Mamer, Luxemborg); C. Michotte (Ceratizit Luxembourg S.á.r.l., Mamer, Luxembourg); C. Mitterer (University of Leoben, Austria); M. Kathrein (Ceratizit Austria GmbH, Austria) Alloying of TiAlN with Ta has been shown to be beneficial in terms of milling and cutting applications. Here we report on the tribological mechanisms present in the range between 25 and 900°C for this coating system, and in particular the effect of bias voltage on the tribological response of the coatings. Based on the results, we provide an explanation for the improved performance of Ta alloyed coatings. An industrial scale cathodic arc evaporation facility was used to deposit the coatings from powder metallurgically produced Ti₄₀Al₆₀ and Ti₃₈Al₅₇Ta₅ targets. Coating structure and chemical composition were studied using X-ray diffraction (XRD) and glow discharge optical emission spectroscopy (GDOES). Coating hardness was determined by nanoindentation, and the tribological behaviour was investigated using a high-temperature ball-on-disc tribometer and an optical profilometer. Fracture cross sections after tribological testing were investigated by scanning electron microscopy (SEM). With increasing bias voltage, the structure changes from a dual-phase face-centered cubic (fcc) and hexagonal (hex) to a single-phase fcc structure. Ta alloyed coatings show a significantly higher resistance to oxidation than unalloyed TiAlN. At room temperature, the massive abrasive wear is independent from bias voltage. At elevated temperatures, wear depends on bias voltage. For the respective temperature range, different controlling effects have been identified. The results show that the bias voltage affects the tribological response at elevated temperatures, where Ta alloying is especially beneficial at very high temperatures.