| In the present dissertation, Y2O3-CeO2 additive system was chosen for preparing metastable tetragonal phase zirconia. Various (Y,Ce)-ZrO2 ultrafine powders with different content of Y2O3 and CeO2 were successfully synthesized by the method of chemical co-precipitate, then these partially stabilized (Y,Ce)-ZrO2 ceramics were sintered. It was found that, compared with CeO2, Y2O3 exhibited stronger capability of restraining the growth of zirconia grains. With the increase in mole content of CeO2, the tetragonal phase content in 1 .5mol%Y2O3-ZrO2 increased till monoclinic phase disappeared, and the stability of tetragonal phase became stronger and stronger even some of them could not be transformed easily. (Y,Ce)-ZrO2 ceramics characterized with the microstructure of transformation toughening, micro-crack toughening and the effect of grain drawing-out. (1.5mol%Y2O3, 4mol%CeO2)-ZrO2 ceramic had the most abundant of tetragonal phase which could transform into monoclinic phase. The bending strength of the sample was as high as 660MPa, and the fracture toughness and the hardness reached 10.8 MPa-m1/2 and 10.12GPa respectively.Densification temperatures for (Y,Ce)-ZrO2/ Al2O3 multi-phase ceramics increase with the weight content of AbCb increasing. The effect of the sintering temperature on the mechanical properties could contribute to that of the relative densities. In the present dissertation, the mechanical properties of (Y,Ce)-ZrO2/ Al2O3 multi-phase ceramics and their abrasion characteristics with GCr15 steel pairs under the dry friction and various applied stresses had been investigated. The results indicated that, proper sintering temperature and appropriate ratio of (Y,Ce)-ZrO2 to Al2O3 assured better coherence between grains, and strong grain boundaries and fine particle structures were achieved, which was beneficial to exerting the effects of the stress induced transformation toughening of ZrO2 and dispersion strengthening of Al2O3. Moreover, the interaction of (Y,Ce)-ZrO2 and Al2O3 decided the characteristics of abrasion performance of the (Y,Ce)-ZrO2/ Al2O3 multi-phase ceramics.It is found that, with the variety of (Y,Ce)-ZrO2 content, the change of theinmechanical properties for these multi-phase ceramics exhibited a saddle shape which could be divided into three zones. They were ZTA zone (the content of ZrO2 is 0-50wt%); Transition zone (the content of ZrOi is 50-70wt%) and ADZ zone (the content of ZrO2 is 70-100wt%).In ZTA zone, there existed effects of stress induced transformation toughening of ZrO2 and the restraining of the growth of Al2O3. The bending strength and fracture toughness increased with the increase of ZrO2 content. The action of the stress induced transformation toughening of ZrO2 was an anti-abrasion mechanism in the present study. The introducing of ZrO2 led to a deceasing trend in the hardness. Under the condition of low applied stresses, the hardness played the key role and wear mechanism exhibited the plastic deformation. As for the high applied stresses condition, the action of the stress induced transformation toughening of ZrO2 turned out to be the main influence and thus the wear exhibited the plastic deformation and brittle fracture mechanism.In ADZ zone, the dispersed Al2O3, which served as the second phase and had a high elastic modulus, exerted the dispersion strengthening effect and restrained the growth of ZrO2. With Al2O3 content increasing, the bending strength and fracture toughness increase monotonously due to the piling up of the actions of the stress induced transformation toughening of ZrO2 and dispersion strengthening of Al2O3. Therefore, the abrasion rate decreased obviously and the anti-abrasion performance of the multi-phase ceramic was improved. Under the low applied stresses, the wear mechanism characterized as the plastic deformation and a small amount of brittle fracture. When high stresses were applied, the wear mechanism of the multi-phase ceramics turned to be the brittle fracture due to the fractures along the interfaces and the particles' d...
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