Effect of the Strength of the Parent Phase on the DrivingForce for the Martensitic Transformation of Partially Stabilized Zirconia

1. 采用3Y、0.75Y-3Ce、1.5Y-6Ce、2.25Y-9Ce和12Ce （Y和Ce分别表示氧化锆中Y_2O_3和CeO_2的摩尔百分比）五种不同的成分制备了四相（四方氧化锆多晶）样品，研究了成分和晶粒尺寸对样品强度的影响。通过烧结后退火对试样的晶粒尺寸进行了改性。维氏硬度计测定的四方相强度随铈含量（或钇含量）的增加而单调下降，但随铈含量的增加而下降的速度越来越快。霍尔-佩奇关系很好地近似了晶粒尺寸的依赖性。因此，两种极端组分的硬度由以下经验方程表示：3y-TZPHv= 1250-0.90 (T-293) +100 (d^<-0.5>-1.21)，其中T表示温度，单位为K， d表示晶粒尺寸，单位为微米。成分对转变温度的影响上述实验所用的试样除少数外，均未经过低至液氮温度的冷却而发生转变。因此，制备了钇含量较低的样品，用于Ms和As的温度测量。这些温度由方程表示为：As=1459-269Y <Y<3Ms=1279-364Y <Y<1.5由于2Y的Ms低于77K，所以当Y含量超过2mol%时，As-Ms测量的驱动力迅速增加。这不能用自由能的变化或硬度随Y含量的增加而增加来解释。需要进一步的研究来解释Ms温度的这种剧烈变化。

1. The effect of the composition and the grain size on the strength of the parent phaseTZP (Tetragonal Zirconia Polycrystals) specimens were prepared with five different composition, namely 3Y,0.75Y-3Ce, 1.5Y-6Ce, 2.25Y-9Ce, and 12Ce, where Y and Ce denote mol% of Y_2O_3 and CeO_2 in zirconia, respectively. The grain size of the specimens was modified by post sinter annealing.The strength of the tetragonal phase as measured by Vickers hardness tester decreased monotonically with increasing ceria content (or decreasing yttria content), but the rate of the decrease became increasingly steep with increasing ceria content. The grain size dependence was reasonably well approximated by the Hall-Petch relation. Thus, the hardness of the two extreme compositions was represented by the following empirical equations :Hv=1250-0.90 (T-293) +100 (d^<-0.5>-1.21) for 3y-TZPHv= 950-0.68 (T-293) +430 (d^<-0.5>-0.72) for 12Ce-TZPwhere T denote temperature in K and d grain size in micrometer.2. The effect of the composition on the transformation temperatureThe specimens used in the above experiment did not transform by cooling as low as liquid nitrogen temperature except a few. Thus, specimens with lower yttria content were prepared for the Ms and As temperature measurement. These temperatures were represented by the follwing equations :As=1459-269Y for0<Y<3Ms=1279-364Y for0<Y<1.5Since the Ms of 2Y was below 77K,the driving force as measured by As-Ms rapidly increased when Y content exceeds 2mol%. This is unlikely to be explained by the free energy change or hardness increase with the increasing Y content. A further study is necessary to explain this drastic change of Ms temperature.