FRICTION PROPERTIES OF WS2 GRAPHITE FLUORIDE THIN-FILMS GROWN BY PULSED-LASER DEPOSITION/

Graphite fluoride (CFx) is investigated as an additive for WS, thin fi lms to reduce its sensitivity to moisture. The films are grown onto ha rdened 440C stainless steel disks by pulsed laser deposition using the 248 nm line from an excimer laser. Substrate temperature and additive concentration are varied to control film chemistry and crystal struct ure. The effect of relative humidity (i.e., < 1 to 85% RH) on friction is evaluated, Coatings grown at RT from targets with a low concentrat ion of CFx exhibit ultralow friction (ULF) behavior in dry air (i.e., mu less than or equal to 0.01), but friction increases with RH. Mechan isms for the ULF behavior are proposed which suggest that further redu ctions in friction are possible. Films grown at 300 degrees C or with higher concentrations of CFx are relatively insensitive to humidity, b ut have more typical friction coefficients (mu less than or equal to 0 .04) in dry air.