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temperature. °c figure 1. - effect of temperature on microhardness and friction coefficients of coating materials. friction measured for cast inconel pins sliding on o.om-mm thick coatings fusion-bonded to precipitation-hardened inconel x-750 disks in air at 2.5 M/s under 500-gm load, 4.8-mh pin tip radius.

(Ref. 1). These materials are known to be strain rate sensitive (Ref. 2) (at least at low strain rates), and this may be a factor 1 n the apparently lower transition temperatures In the hardness tests. Fluoride coatings have been shown to be lubricious above 400 °C, but ineffective as lubricants at lower temperatures (Ref. 3). Therefore, there is an apparent correlation of the brittle to ductile transition temperature with the friction transition temperature.

Since silver films are lubricative at the lower temperatures, and the fluorides discussed are lubricative at higher temperatures than silver, it is reasonable that a composite coating containing silver and the fluorides might be lubricious over a wide temperature range, and this has been shown many times to be the case (e.g., Refs. 3 to 5).

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