Failure analysis of a ceramic ball race bearing made of Y-TZP zirconia

• We investigated a full ceramic bearing (ZrO2-races, Si3N4-rolling bearing balls) which failed during service.
• The bearing failed because of premature wear.
• Raman spectroscopy showed that a phase transition from the tetragonal to the monoclinic phase occurred.
• The transformation was increased by corrosion mechanisms.
• It can be concluded that Y-TZP is not optimal for the use in a rolling bearing under the given conditions.

Full ceramic ball bearings have some advantages compared to conventional steel bearings. They have for instance higher stiffness and hardness, lower density and reduced friction. Because they need less lubrication than steel bearings and owing to their wear and corrosion resistance they are generally materials of choice for pharmaceutical and food industries.In this work a full ceramic bearing that was used in a small mixer in the pharmaceutical industry is investigated. The bearing, consisting of two ZrO2 rings and silicon nitride balls in between, was damaged during service because of premature wear. A failure analysis is performed by fractography and Raman spectroscopy, and it is shown that a stress induced phase transition from the tetragonal to the monoclinic phase was the reason behind the failure of the ZrO2-rings.