Effects Of Surface Grinding On Surface Quality And Strength Of Oxide Ceramics

Oxide ceramics are widely used in medicine,chemical industry,aerospace and other fields due to the high wear and temperature resistance and excellent chemical stability.A higher requirement for the surface quality of oxide ceramics has been put forward to adapt the rapid development in these fields.At present,the grinding process is one of the most commonly used methods for ceramic surface processing due to the high precision of grinding and high material removal rate.Therefore,it is greatly significant to clarify the relationship among grinding processing methods,surface quality and mechanical properties.The surface processing of Al₂O₃,ZrO₂ and Zirconia-toughened alumina?ZTA?ceramics was performed using the precision grinding/polishing machine and grinding machine.The effect of different grinding conditions involving grinding disc speed,the abrasive grain size of grinding disc or wheel,the longitudinal feed or horizontal translation speed of grinding wheel on the surface quality,surface residual stress and mechanical properties of ceramics were investigated and discussed.The main conclusions or results are shown as follows:A more rough surface?such as the processing scratches?is observed on the surface of Al₂O₃ceramic after the grinding machine processing,indicating that the surface processing used by grinding machine has a greater influence on the surface quality of Al₂O₃ ceramic compared to the grinding disc processing.Furthermore,the removal mechanism of Al₂O₃ ceramics during grinding processing is a mixture of brittle removal and ductile removal,and the surface residual stresses exhibit compressive stress after processing.Especially,the removal mechanism of Al₂O₃ceramics is mainly ductile removal and the surface residual compressive stress is up to-241 MPa in the case of fine abrasive grain size of grinding disc or wheel,large grinding disc rotation speed,small longitudinal feed and large horizontal translation speed of grinding wheel.The surface roughness,microstructure and surface residual stress have a comprehensive effect on the bending strength of Al₂O₃ ceramics.The bending strength increases to 528 MPa with decreasing the surface roughness and residual compressive stress of Al₂O₃ ceramic.The maximum bending strength of ZrO₂ ceramics after grinding by the same process is 905MPa compared with Al₂O₃ ceramic.An excellent surface quality of ZrO₂ ceramics presents after grinding,and the minimum surface roughness is about 0.03?m.Generally speaking,the surface roughness and residual compressive stress of ZrO₂ ceramics decrease with the increase of the mesh size of grinding disc,resulting into a lower bending strength.Moreover,the surface of ZrO₂ ceramics show more smoothness and the removal mechanism is mainly ductile removal under the conditions of large grinding wheel mesh,lateral translation speed of the grinding machine and small feed rate,resulting into a larger surface residual compressive stress and higher bending strength.It is worth noting that a higher bending strength can be obtained in the case of a small grinding disc mesh and a large grinding wheel mesh.This is because of the presence of martensitic transformation,which can inhibit the extension of cracks.The surface microstructure of ZTA ceramics after grinding is similar to Al₂O₃ ceramics with many fractures and pits.However,the surface of ZTA ceramics present a large ductility area and a small roughness,and the ceramic has a larger residual compressive stress and higher bending strength under the condition of large grinding disc/grinding wheel mesh,high grinding disc speed/grinding machine lateral movement speed.The grinding process has a great influence on the bending strength of ZTA ceramics,showing a great difference between the minimum?364MPa?and maximum?769 MPa?bending strength.In summary,the bending strength of ceramics is comprehensively determined by their properties,the surface roughness,defects,and residual surface stress after grinding.