Tribological properties of nanoscale alumina-zirconia composites

The tribological properties of zirconia (Y-TZP), alumina and their composit es, alumina dispersed in zirconia (ADZ) and zirconia-toughened alumina (ZTA ), were investigated. These ceramics are made by colloidal processing metho ds such that well-defined, homogeneous microstructures with submicron grain s and few defects are obtained. Dry sliding tests against alumina balls wer e performed on a pin-on-disc tribometer using varying test conditions. It w as shown that, with initial Hertzian contact pressures up to 1 GPa and slid ing velocities up to 0.5 m/s, the specific wear rate was the highest for Y- TZP, 10(-6) mm(3)/(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 mecha nisms are abrasion, delamination and polishing. The coefficients of frictio n were as high as 0.8 for Y-TZP and as low as 0.45 for ZTA. The main conclu sion of this work is that ZTA composites manufactured and tested in this st udy have a superior wear resistance and a relatively low coefficient of fri ction under dry sliding conditions. (C) 1999 Elsevier Science S.A. All righ ts reserved.