Friction silicon nitrides

Example 11.4. McGuiggan et al. [492] measured the friction on mica surfaces coated with thin films of either perfluoropolyether (PFPE) or polydimethylsiloxane (PDMS) using three different methods The surface forces apparatus (radius of curvature of the contacting bodies R 1 cm) friction force microscopy with a sharp AFM tip (R 20 nm) and friction force microscopy with a colloidal probe (R 15 nm). In the surface force apparatus, friction coefficients of the two materials differed by a factor of 100 whereas for the AFM silicon nitride tip, the friction coefficient for both materials was the same. When the colloidal probe technique was used, the friction coefficients differed by a factor of 4. This can be explained by the fact that, in friction force experiments, the contact pressures are much higher. This leads to a complete penetration of the AFM tip through the lubrication layer, rendering the lubricants ineffective. In the case of the colloidal probe the contact pressure is reduced and the lubrication layer cannot be displaced completely. 

Wayne, S.F. and Buljan, S.T. Microstructure and wear resistance of silicon nitride composites , in Friction and Wear of Ceramics, ed. S. Jahanmir, pp. 261-285, Marcel Dekker, New York (1994). 

C. R. Blanchard and R. A. Page, Effect of Silicon Carbide Whisker and Titanium Carbide Particulate Additions on the Friction and Wear Behavior of Silicon Nitride, J. Am. Ceram. Soc., 73[11], 3442-3452 (1990). 

Gangopadhyay et al investigated the use of graphite intercalated with nickel chloride NiClj to lubricate silicon nitride or alumina sliding against a steel counterface. The lubricant was quite effective, reducing the coefficient of friction from 0.5 to 0.17 for silicon nitride, and from 0.55 to 0.18 for alumina. There is no obvious reason to expect that the behaviour of molybdenum disulphide would be significantly different. 

H. Tomizawa and T.E. Fischer, Friction and wear of silicon nitride and silicon carbide in water Hydrodynamic lubrication of low-sliding speed obtained by tribochemical wear, ASLE Trans., 30, 41-46, 1986. 

T.E. Fischer and H. Tomizawa, Interaction of tribochemistry and microfracture in the friction and wear of silicon nitride, Wear, 105, 21, 1985. 

Table II presents the specific wear rates (in mm /Nm, volume loss per unit load per unit sliding distance) and average kinetic friction coefficients of the composites sliding versus steel and silicon nitride, upon initial and continued sliding. Plots of friction coefficient versus sliding duration in kilocycles (1 kc = 107 m) are shown in Figures 2-5, for all experiments. All composites formed transfer films upon sliding against both steel and silicon nitride. The films were similar in appearance under optical microscopy, and covered approximately 30% of the contact region.

Figure 4. Friction coefficient as a function of sliding duration for LI composites sliding against silicon nitride.

Since the major component of lubricant 1 (WSe2) and all components of lubricant 2 are layer lattice transition metal dichalco-genides, it is at first difficult to explain the large differences in frictional behavior observed between LI and L2 composites sliding against silicon nitride. We advance here a hypothesis for involvement of the phosphate additive in adverse reactions both with the ceramic counterface and with lubricant 1. 

M. Herrmann, I. Schulz, Chr. Schubert and W. Hermel, Silicon Nitride Materials with Low Friction Coefficients , Key Engineering Materials, 161-163, 1999, 599-602. 

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