BOUNDARY FILM FOR STRUCTURAL CERAMIC MATERIALS

Structural ceramic materials, like metals, will require lubrication if they are to be used extensively for tribological applications. The us e of thin soft metallic coatings (specifically Ag) as a boundary film during mineral oil lubrication of silicon nitride (Si3N4) and zirconia (ZrO2) ceramic materials was investigated in this study. With a pin-o n-flat contact configuration in reciprocating sliding, the steady fric tion coefficient was reduced by a factor of two (0.14-0.16 vs. 0.06-0. 07) when the flats were coated with Ag. Also, with Ag coatings, the we ar of pins was reduced to an unmeasurable level,whereas, in the absenc e of Ag coatings specific wear rates of about 2 X 10(-9)-4 x 10(-8) mm 3 N-1 m-1 and about 7 X 10(-8)-2 X 10(-7) mm3 N-1 m-1 were measured fo r Si3N4 and ZrO2 pins respectively. In addition to preventing direct c ontact between pins and flats, thereby reducing wear, the Ag coatings also act as a solid lubricant, help dissipate flash heating, and accel erate modification of the lambda ratio.