Microstructure and tribological properties of ZrO2(Y2O3) matrix composites doped with different solid lubricants from room temperature to 800 °C

In this paper, spark plasma sintering is employed to synthesize a variety of self-lubricating ZrO2(Y2O3) matrix composites by tailoring the chemical compositions. The additives of BaF2, CaF2, Ag, Ag2O, Cu2O, BaCrO4, BaSO4, SrSO4 and CaSiO3 were incorporated into the ceramic matrix to evaluate their potentials as effective high-temperature solid lubricants from room temperature to 800 °C by using a ball-on-block friction and wear tester in sliding against alumina ball. For a comparative study, ZrO2(Y2O3) matrix composites incorporated with and without graphite or MoS2 were also investigated under the identical test conditions. The relationships among composition, microstructure and tribological properties of the composites are investigated to identify their self-lubrication mechanisms. The unlubricated ZrO2(Y2O3)-Al2O3 (TZ3Y20A) ceramics have a friction coefficient of 1.15 and a wear rate in the order of 10−4 mm3/Nm at 800 °C, while the TZ3Y20A-SrSO4 composites exhibit a steady-state friction coefficient of less than 0.2 and a wear rate in the order of 10−6 mm3/Nm from room temperature to 800 °C. Surface fatigue and brittle fracture are considered as the dominating wear mechanism of unmodified TZ3Y20A ceramics at 800 °C. However, for self-lubricating TZ3Y20A-SrSO4 composites, the formation, plastic deformation and effective spreading of SrSO4 lubricating films are the most important factor to reduce friction and wear rate over a wide temperature range.