FRICTION AND WEAR OF ZRO2-TIO2 SURFACE-ALLOYED AL2O3 CERAMICS IN UNLUBRICATED SLIDING CONTACT

Slightly and highly porous Al2O3 ceramics were surface remelted and al loyed by adding ZrO2 and TiO2 using infrared CO2 laser radiation. The resulting composite layers of thickness of about 200 mum contained abo ut 31 vol.% of ZrO2- and TiO2-rich phases which were homogenously dist ributed at the grain boundaries of the alumina matrix. Microstructures and worn surfaces were analysed by electron microscopy and EDX analys is. Tribological tests were carried out unlubricated using conditions of abrasive wear and oscillating sliding wear, respectively. The resul ts showed that the average grain size and hardness of the ceramics wer e reduced due to alloying. Despite decreasing hardness the wear resist ance was substantially increased. Friction and wear of the untreated c eramics depended strongly on the amount of porosity which was removed or substantially reduced by laser treatment. Surface alloying of Al2O3 ceramics can offer an effective process for producing components show ing very different surface and bulk properties and particularly improv ed tribological behaviour. For the alloying elements and experimental conditions used, the improvement was more pronounced in wear resistanc e than in friction coefficient.