The effect of deposition parameters on the wear properties of yttria-stabilized zirconia overcoats

Yttria-stabilized zirconia was rf-diode sputtered over a 250-nm chromium underlayer on textured aluminum-NiP 130-mm-diam substrates. Tribological properties of the overcoat were evaluated via contact start-stop (CSS) testing, as a function of oxygen partial pressure, substrate bias potential, and argon pressure. Depending on deposition conditions, a wide range of friction and wear properties was observed. Lower oxygen partial pressures (<0.01 Pa) produced the lowest average friction levels of 0.3–0.5 after 30 000 CSS. Use of high argon sputtering pressures (>1.6 Pa) produced overcoats which demonstrated definite wear and often crashed during contact stop-start testing. SEM and TEM photographs revealed that the overcoats with poor wear characteristics had significantly different grain sizes and higher void contents than overcoats with superior wear properties deposited at lower argon pressures. Application of a fluorocarbon surface lubricant reduced average friction levels after 30 000 CSS from 0.8 on an unlubed disk to 0.35.