Simultaneous effect of CaF2 and TiC on tribological properties of ZTA ceramics for high temperature application

Abstract

Liquid lubrication poses risk to environment; it can vaporize under high temperature or vacuum. Solid lubricant has the potential to replace liquid lubricants due to better stability at severe working environment. This work has been focused to improve tribological properties of zirconia toughened alumina (ZTA) by adding an optimized 4 wt% of CaF2 as a solid lubricant. Since CaF2 is softer material it degrades the mechanical properties of ZTA. To make a balance between the mechanical and the tribological properties, a comparatively harder material TiC is added simultaneously by 10 wt%. All the ceramic composites have been consolidated by hot press sintering at 1500 °C with 30 mins holding time under uni-axial pressing of 50 MPa. Four samples: ZTA, ZTA_CaF2, ZTA_TiC and ZTA_TiC_CaF2 were prepared through the same route. The relative density of the sample (ZTA_CaF2_TiC) achieved was 96.4%. The hardness and fracture toughness has been measured as ∼15GPa and ∼5 MPa m1/2 respectively for the hybrid ceramic composite which is better than ZTA_CaF2 ceramic composite. The tribological characteristics have been evaluated using high temperature tribo-meter with a ball on disc arrangement at 600 °C in vacuum condition. The COF of the ZTA_CaF2 has also been improved by ̴ 39 % compared to the main composite due to the self-lubricating film formation on wear track. A considerable improvement as ∼24.5% in coefficient of friction (COF) and ∼40% in specific wear rate has been found in hybrid ceramic composite as compared to the ZTA ceramic. Thus, it can be used for developing self-lubricating components used in high temperature application.