Strength measurement of thin lubricating films

A new method has been developed to measure the film-failure maximum shear stress at surface tau(sm) of thin films in sliding. A ball-on-inclined plane scratch test was employed in these measurements. The tested balls were 52100 steel and the tested plane samples were 52100 steel, sapphire and a silicon wafer. Films on the plane samples were dip-coated to different thickness (0.5-200 nm). Paraffin, oleyl alcohol, octadecanol, octadecamide, n-octadecyl mercaptan, 1,2-octadecanediol, octadecylamine, oleic acid, stearic acid, ZDDP, etc. were used to deposit different films. The test results indicate that the film-failure maximum shear stress at surface tau(sm) increases with an increase of film thickness. Roughness and substrate differences are also found to have an influence on the measured tau(sm). A smoother surface gives higher tau(sm). Among the studied films, stearic acid possesses the highest tau(sm) while octadecanol has the lowest. (C) 2000 Elsevier Science S.A. All rights reserved.