Dual Tribological Behavior of a Nanolayered Ceramic: Ti 3 SiC 2
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Dual Tribological Behavior of a Nanolayered Ceramic: Ti3SiC2 Alexandra Souchet, Julien Fontaine, Michel Belin, Thierry Le Mogne, Jean-Luc Loubet, Ecole Centrale de Lyon, LTDS, UMR CNRS 5513, Ecully, France. Michel W. Barsoum, Department of Materials Science and Engineering, Drexel University, Philadelphia, USA.
ABSTRACT The MAX phases are new, thermodynamically stable, nanolayered ternary carbides and nitrides. These materials have a big potential in tribological applications due to their structure, similar to graphite or molybdenum disulfide. For example, the friction coefficients of the basal planes of Ti3SiC2 have been shown to exhibit very low (< 5 x 10-3) friction coefficients. The aim of this study is to better understand the tribological behavior of polycrystalline Ti3SiC2 against stainless steel. Experiments were conducted on a ball-on-flat tribometer (~ 25°C and ~ 30% relative humidity) that simultaneously measures friction coefficients and electrical contact resistance. Different stainless steel ball diameters and normal loads were used and resulted in contact pressures between 0.35 and 1.25 GPa. Two different tribological behaviors were observed, both with relatively low friction coefficients for ceramics. The first behavior, referred to as type I, is characterized by low friction coefficients (≈ 0.15); low wear and a transfer film containing titanium and carbon formed on the ball. The other behavior, type II, is characterized by friction coefficients that starts at ≈ 0.15, and then increases to about 0.4. At the end of the experiment, the ball is worn, and compacted wear debris containing iron can be found on the plane. The two behaviors seem to be independent of contact pressure, but are rather sensitive to normal applied load. The transition between these two regimes will be discussed.
INTRODUCTION Ti3SiC2 is one of the thermodynamically stable nanolaminates comprising the MAX phase family. The structure of these ceramics, derived from the hexagonal one, is Mn+1AXn, with n = 1 to 3, M a metal, A an element of the A-group and X being carbon and/or nitrogen. Ti3SiC2 has been the most studied of these compounds. It is elastically stiff (Young’s modulus of 325 GPa), has a relatively low hardness (~ 4 GPa), is electrically and thermally conductive, readily machinable, resistant to thermal shock and unusually damage tolerant for a ceramic [1]. The MAX phases deform by a combination of kink and shear band formation, with the delamination of individual grains. Dislocations multiply and are mobile at room temperature, and glide exclusively on the basal planes. Despite all the studies that have been conducted on Ti3SiC2, only few papers have been devoted to its tribological behavior. Using lateral force microscopy, Myhra et al. [2] showed that the basal planes of Ti3SiC2 have friction coefficients that are ultra-low (2×10-3 to 5×10-3). Macroscopical experiments against stainless steel conducted afterwards by El-Raghy et al. [3], and Sun et al. [4], gave friction coefficients with two stages, respective
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