Tribological properties of nanoscale alumina-zirconia composites

The tribological properties of zirconia (Y-TZP), alumina and their composites, alumina dispersed in zirconia (ADZ) and zirconia-toughened alumina (ZTA), were investigated. These ceramics are made by colloidal processing methods such that well-defined, homogeneous microstructures with submicron grains and few defects are obtained. Dry sliding tests against alumina balls were performed on a pin-on-disc tribometer using varying test conditions. It was shown that, with initial Hertzian contact pressures up to 1 GPa and sliding velocities up to 0.5 m/s, the specific wear rate was the highest for Y-TZP, 10¿6 mm3/(N m), and the lowest for ZTA, 10¿9 mm3/(N m). For both single-phase zirconia and alumina ceramics, it was found that addition of a harder (alumina) or a tougher (zirconia) phase, respectively, leads to an improved wear resistance. Depending on the test conditions, the wear mechanisms are abrasion, delamination and polishing. The coefficients of friction were as high as 0.8 for Y-TZP and as low as 0.45 for ZTA. The main conclusion of this work is that ZTA composites manufactured and tested in this study have a superior wear resistance and a relatively low coefficient of friction under dry sliding conditions.