Nano-scratch and nano-indentation were used to determine hardness, elastic modulus, adhesion, friction and wear resistance of chromium oxide coatings in air and in water. The friction coefficient is higher in water, compared to air, and it increases with the applied normal load, although there are no obvious differences in hardness and elastic modulus in air vs. water. A higher normal load increases the wear volume; while the wear rate decreases with the number of wear cycles due to machining hardening. A reduction in coating adhesion was observed in water when the normal load exceeded a critical value of 1.8 N.
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