Reactive deposition of aluminium oxide coatings on PTFE substrate

Aluminium oxide coatings were deposited on to polytetrafluoroethylene (PTFE) substrates by the reactive sputtering technique in a closed-field unbalanced magnetron sputtering (CFUBMS) system. The effects of sputtering parameters on wear performance and on the structure of the coatings were investigated. The resulting coatings were analysed by microanalyser, scanning electron microscope (SEM) and a ball-on-disc wear test. Depending on the preparation conditions, the coatings were shown to have different compositions and different mechanical properties. The results revealed that ductile, dense coatings could be obtained in a low oxygen concentration plasma, while a high oxygen concentration in the plasma results in a granular, porous structure to the coatings. The coatings with a medium Al/O ratio exhibited good wear and impact resistance; high Al/O ratio coatings adhere to the substrate well and possess good impact resistance, but have low wear resistance; and low Al/O ratio coatings possess poor impact resistance, and are prone to cracking and debonding of the coating due to substrate yielding during a ball-on-disc wear test.