FRETTING BEHAVIOR OF HARD COATINGS UNDER HIGH NORMAL LOAD

Surface damage of worn material and cracks due to fretting can be offset by the use of hard coatings. The present study shows the results which have been obtained using titanium nitride and diamond-like carbon coatings 5 mu m thick deposited on high speed steel. The fretting experiments were conducted with a 10 mm diameter steel ball (AISI 52100) sliding on a coated hat surface with a normal load ranging from 100 to 500 N. The sliding amplitude (peak-to-peak displacement) of the ball is constant during the test, that is between 5 and 50 mu m. The experiments were performed under room atmosphere at ambient temperature. The results obtained demonstrate the changes related to the presence of the coating: the fretting maps are modified because of a different surface nature and mechanical properties. An energy ratio (dissipated energy divided by total energy during a fretting cycle) has been found to be very useful to describe the contact phenomena.