Sliding Wear Properties of Self‐Mated Yttria‐Stabilized Tetragonal Zirconia Ceramics in Cryogenic Environment

The objective of the present work is to investigate the friction and wear of self‐mated ZrO 2 ceramics in a cryogenic environment. Using a specially designed high‐speed cryo‐tribometer, fine‐grained yttria‐stabilized tetragonal ZrO 2 polycrystals (Y‐TZP) were worn at varying loads (5–15 N) with sliding speed of 1.1 m/s in a cryogenic environment (liquid nitrogen, LN2). For comparison, the sliding tests were also conducted under selected operating conditions on self‐mated Y‐TZP under ambient conditions (room temperature (RT)), primarily to understand the difference in wear mechanisms for a given sliding condition. With these planned experiments, it was attempted to answer some important issues: (a) Can sliding in LN2 reduce the coefficient of friction (COF) of self‐mated ZrO 2 ? (b) Does t ‐ZrO 2 transformation occur in a cryogenic environment and if it occurs, how does it affect the fracture behavior? (c) How does the mechanism of wear change from RT to LN2 temperature? In our experiments, high COF (0.35–0.75) and high wear rate of disks 10 −4 –10 −6 mm 3 ·(N·m) −1 have been measured under the selected tribological testing conditions. Interestingly, X‐ray diffraction analysis revealed the presence of o ‐ZrO 2 after sliding in a cryogenic environment, while no change in phase assemblage was recorded after sliding under identical conditions at RT. An important observation has been that severe plastic deformation (wider and deeper grooves) at RT and microcracking (“fish scale” pattern)‐induced spalling of a damaged layer in an LN2 environment are the dominant wear mechanisms, respectively.