Friction of Uncontaminated Coatings

Atmosphere Friction Coefficient Calculated Shear Strength (MPa) 

It is interesting that the authors referred to the need for a transfer film to form on the counterface as a condition of very low friction, although the necessity for the 

In contrast with their exceptionally good performance in vacuum, the performance of Type I coatings in air is generally poor. The friction level in air shown in Table 10.2 is fairly typical, and life in air is also poor. In this context it is interesting that Fayeulle et al found that the transfer films formed from Type I coatings in air were highly oxidised, although still basally-oriented. 

Spalvins ° attributed the poor performance in air to the presence of water, and Roberts further showed that the effect on friction occurs at two different levels and is reversible when testing alternates between moist air and high vacuum. It is significant that the coefficient of friction in moist air of the ultra-pure films produced by Donnet et al ° 0.15, is almost identical with that of the less-rigidly contaminant-free films of Roberts, 0.16. This suggests that the high friction in moist air is almost entirely due to the water present, and is not significantly affected by any other contaminants which may have been present. 

It is generally accepted that coating endurance, especially in moist air, is very dependent on the strength of adhesion of coating to substrate. Fleischauer and Bauer ° came to the conclusion that, just as slight oxidation of the lower layers of 

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