EFFECTS OF A 2ND-PHASE ON THE TRIBOLOGICAL PROPERTIES OF AL2O3 AND ZRO2 CERAMICS

The tribological properties of four different materials are investigat ed, tetragonal zirconia (Y-TZP), Al2O3 dispersed in Y-TZP (ADZ), ZrO2 dispersed in Al2O3 (ZTA) and Al2O3 (with 300 ppm MgO). These materials are used as a cylinder sliding against a plate of Y-TZP (TZ-3Y)). Com pared to Y-TZP, the wear resistance of ADZ composites is increased by a factor of 4-10. At a contact pressure of 230 MPa, a wear transition for Y-TZP is observed from plastic deformation to microchipping and mi crofracture due to the high interfacial temperature (450 degrees C-550 degrees C) generated by frictional heating. Because of the higher ela stic modulus, hardness and fracture toughness at high temperature, ADZ composites show better wear resistance and a higher transition contac t pressure (over 400 MPa) under the present conditions. For Al2O3, the transition from mild to severe wear occurs when the contact pressure is changed from 250 to 400 MPa. For ZTA ceramics, the wear behaviour d oes not change because of the presence of a compressive layer due to t he zirconia phase transformation during sliding. In water the wear res istance for ADZ and ZY5 is almost two orders of magnitude higher than the results under dry conditions. Reduction of the interfacial tempera ture by using water and the formation of a hydroxide layer at the cont act surface by the tribochemical reaction of water with the ceramic, a s observed by XPS, gives a positive effect on wear resistance. (C) 199 7 Elsevier Science S.A.