SHEAR-STRENGTH MEASUREMENTS OF PARALLEL MOSX THIN-FILMS

The effect of Hertzian contact pressure on the friction coefficient of parallel MoSx, films was investigated by sliding sapphire and AISI 52 100 steel against parallel MoS,(x)-coated AISI 440C steel under a wide range of contact loads. Mean initial Hertzian contact pressures in th e range 0.493-1.258 GPa were created between balls and parallel MoS,(x )-coated 440C disks by varying the applied load and the elastic moduli of the balls. The friction coefficient decreased with the increasing load. Using the Hertzian contact model, we estimated that the shear st rength of parallel MoS, films was approximately 40 MPa. This value is higher than that obtained with the usual lamellar MoS2, films. An expl anation in terms of an increasing reactivity of basal surfaces in para llel films is given. The effect of gaseous environment on friction mea surement was also studied by varying the atmosphere conditions. For th is purpose, friction tests were performed in open air and in dry Argon (Ar). The friction coefficient was shown to increase in the presence of water vapour. The shear strength increased with humidity from 40 MP a up to about 80 MPa. An explanation, taking into account the deformat ion microstructures that have been developed during sliding, is propos ed. (C) 1997 Elsevier Science S.A.