Outgassing of stainless steel during sliding friction in ultra-high vacuum

Outgassing of SS surfaces under sliding friction in ultra-high vacuum has been studied by ad-desorption mass-spectrometry and Auger electron spectroscopy. Experiments have been performed at normal loads of the indent in the range from 0.02 up to 0.87N, sweeping frequencies from 48 to 124 min(-1) and linear sliding speed 7.5mm/s. The P-t outgassing curve presents an oscillating current over a continuous one and three well different parts: (i) an initial desorption peak of high intensity, (ii) a region of nearly stable pressure and (iii) a decreasing of the pressure when friction is stopped. The outgassing rate slowly decreases with the number of sweeps. The AES analysis shows that the chemical composition and rugosity of the rubbed area of surface depends on the friction conditions. For loads from 0 to 72 mN, no chemical changes in the surface composition are observed, while for loads up to 870 mN, the concentration of Fe increases and concentration of Cr decreases depending on the friction duration. The outgassing process is a combination of gas diffusing process from the outermost layers and desorption from the surface. (C) 1999 Elsevier Science Ltd. All rights reserved.