Fabrication and tribological properties of titanium nitride coatings incorporating solid lubricant microreservoirs

The concept of incorporating microscopic reservoirs within a hard coating for the purpose of solid lubricant storage and supply during wear of interacting surfaces has been investigated in this study. A novel method was devised using ceramic beads (1.5-10 μm diameter) as placeholders during the deposition of a TiN coating by reactive sputter deposition. A pin-on-disk wear test was used to test these coatings using graphite and sputter-deposited carbon as the solid lubricant, and an alumina counterface. When tested without any lubricant, the presence of the microreservoirs in the TiN coating appeared to degrade the mechanical integrity of the coating leading to rapid failure. With the graphite lubricant present, the frictional behavior ranged from levels similar to the TiN coating alone, to that of graphite alone. Tests of the TiN coating made using 10 μm beads running against an aluminum counterface showed substantial improvement when the microreservoirs were present. Optical microscopy examination of the wear tracks showed the microreservoirs were generally successful at trapping the graphite lubricant during wear. With a sufficient density and appropriate distribution of the microreservoirs significant improvements in tribological performance can be realized.