Study On The Hump Of Zirconia Ceramics

A asymmetric broadening, a hump or even an independent diffraction peaksobserved on the left shoulder of (111)cor (111)tpeaks in both fully and partiallystabilized zirconia treated by surface grinding, ion implantation or heat treatment, forshort “the hump phenomenon”. This thesis study on the origin of the humpphenomenon.zirconia ceramics were fabricated by conventional process and pressurelesslysintering in O2. In order to clarify phase structure changes of zirconia ceramics, theeffects of the ion size of doped stabilizer, the cooling methods of the calcinationssample, the surface grinding of the samples as sintered and the subsequent heattreatment conditions were investigated by X-ray diffraction. In addition, In order tostudy the relationship between surface residual stress and phase structure of zirconiaceramics, surface residual stresses were determined by X-ray diffraction using thesin2ψ method.The results indicate that a hump observed on the left shoulder of (111)tor (111)cpeaks when3Y-TZP or8YSZ treated by surface grinding, and best grinding processwas that: P360c+P800cof grit size,400r/min of rotate speed,17.5N of grindingpressure,5min of grinding time multidirectional for grinding direction. The humpshould be unrelated to the method of cooling or the subsequent heat treatment, whichinduce lattice deformation, but be related to surface grinding. A residual compressivestress, formed as a result of surface grinding, induced tetragonal-to-rhombohedralphase transformation. And the hump was due to the rhombohedral phase (111)rpeaksuperimposed with the tetragonal phase (111)tpeak or the cubic phase (111)cpeak inthe XRD patterns. A positive correlation between the extent of the hump and theresidual compressive stress, and the formation of the hump require for a critical valueof residual compressive stress,396Mpa＜σ＜462Mpa for3Y-TZP and382Mpa＜σ＜413Mpa for8YSZ.16mol%calcium stabilized zirconia (16Ca-ZrO2) and16mol%cerium stabilizedzirconia (16Ce-ZrO2) powder were prepared by liquid-phase method, and thensintered into a ceramic disk. The results of heat treatment at1300℃for16Ca-ZrO2 indicate that the more lattice deformation does not cause the more hump phenomenon.A residual compressive stress, close to8YSZ’s, formed as a result of16Ca-ZrO2treated by surface grinding. Different stabilizers may affect the critical residual stressof the formation of the hump, and the16Ca-ZrO2’s is larger than the8YSZ’s. Thehump formed when16Ce-ZrO2treated by surface grinding, at the same time, alsoinduce tetragonal-to-monoclinic phase transformation, and the residual compressivestress was670Mpa.In conclusion, the hump was not because of lattice deformation but due to thenewly generated phase, formed as a result of phase transformation induced by residualcompressive stress when zirconia ceramics treated by surface grinding, superimposedwith the main phase in the XRD patterns.