Microstructure–toughness–wear relationship of tetragonal zirconia ceramics

The goal of the present work is to investigate the influence of microstructural variables (grain size, overall yttria content and yttria distribution) and toughness on the tribological behavior of yttria-stabilised tetragonal zirconia (Y-TZP) ceramics. Unlubricated fretting tests were performed on Y-TZP ceramics against commercial hardmetal (WC-Co) ball under ambient conditions of temperature and humidity. The ceramics were processed from commercial yttria-coated and co-precipitated powder as well as the newly formulated powder mixtures with varying overall yttria content and yttria distribution. Microstructural investigation of the worn surfaces was performed and the wear mechanisms were studied. Based on the measured tribological data, the relationships among the friction coefficient, wear, toughness and microstructural variables were elucidated. Within the investigated fretting regime, phase transformation (tetragonal to monoclinic zirconia) induced microcracking and spalling was found to play a major role in the wear of high toughness TZP ceramics. The significant outcome of our research is that a trade-off between the fracture toughness and the wear resistance is achieved in the newly processed Y-TZPs.