THE NATURE OF THE LUBRICATING FILMS FORMED BY CARBON-TETRACHLORIDE UNDER CONDITIONS OF EXTREME-PRESSURE

The temperature T between the lubricated surfaces in a pin and v-black apparatus is given, for any lubricant at an ambient temperature of T- 0, by the formula T = T-0 + Kr omega mu L where r is the radius of the pin, omega its rotational angular velocity, K a constant that depends on the thermal conductivity in the region of the contact between the pin and the v-bIock and L the applied load. The product Kr omega has b een determined previously for the pin and v-block apparatus and the co efficient of friction it can be measured from a plot of the torque req uired to rotate the pin versus applied load, The rare of material remo val can also be measured From the width of the wear scar formed on the face of the v-block: by the rubbing motion of the pin. Asymptotes in the plot of removal rate versus applied load have been shown to corres pond to melting of the material that forms the anti-seizure film at th e interface, so that measurement of the corresponding interfacial temp erature yields its melting point, and therefore indicates the nature o f the film. Using this strategy, it is shown that FeCl2 forms the lubr icating layer at low loads when CCl4 is used as the lubricant additive . In addition, films grown by the thermal decomposition of CCl4 vapor on an iron foil also consist of iron chloride. Mossbauer analysis of f ilms deposited from CCl4 vapor at higher temperatures (similar to 1050 K) show the formation of iron carbide (consisting of Fe3C). The tribo logical behavior is in accord with this observation since at higher lo ads, and therefore higher surface temperatures, asymptotes in the rate of film removal correspond to the melting of iron carbide (Fe3C) whic h is therefore proposed to form the anti-seizure film under these cond itions. Ultimately, at the highest attainable loads, the asymptote in the removal rate curve suggests that a carbon film acts as the solid l ubricant.