Preparation of Chameleon Coatings for Space and Ambient Environments (Preprint)

Tribological coatings of yttria stabilized zirconia (YSZ), gold, diamond like carbon (DLC) and MoS2 were synthesized using magnetron assisted pulsed laser deposition (MSPLD). The coatings were synthesized in four-component and three-component combinations that included YSZ/Au/DLC/MoS2, YSZ/Au/MoS2, and YSZ/Au/DLC. A range of coating compositions was studied to explore coating optimization for low friction in varying environments (dry, humid and high temperature). For four-component YSZ/Au/DLC/MoS2 coatings, the optimal compositions for friction adaptation between dry nitrogen and humid air included relatively high concentrations of the soft phase, Au (>20 at. %), and low amounts of the hard phases, DLC and YSZ. Ex situ Raman spectroscopy analysis indicates that friction adaptation involves a combination of both lubricating species, MoS2 and carbon where transitions of DLC to graphitic-carbon and amorphous MoS2 to its hexagonal phase occurs after cycling between both room temperature humid air and dry nitrogen. In large carbon concentrations (>30 at. %), the DLC component was found to be detrimental for friction in dry nitrogen and humid air, but promoted a longer coating wear life at 500 deg C. The three-component coating of YSZ/Au/MoS2 performed well in both dry nitrogen and humid air, suggesting a synergism between Au and MoS2, where carbon was not necessary for lubrication in humid air.