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

1.制备了5种不同成分的TZP（TetraxylZrO_2 Polycrystals）试样，即3 Y、0.75Y-3Ce、1.5Y-6Ce、2.25Y-9 Ce和12 Ce，其中Y和Ce分别表示ZrO_2中Y_2O_3和CeO_2的摩尔百分比。通过烧结后退火对试样的晶粒尺寸进行了调整，用维氏硬度计测得的四方相的强度随氧化铈含量的增加（或氧化钇含量的减少）单调下降，但下降的速率随氧化铈含量的增加而变陡。的晶粒尺寸的依赖性是合理的近似Hall-Petch关系。因此，两种极端成分的硬度由以下经验公式表示：对于3 y-TZPHv =1250-0.90（T-293）+100（d^<-0.5>-1.21）<-0.5>对于12 Ce-TZP其中T表示温度（K），d表示晶粒尺寸（微米）.成分对相变温度的影响除少数试样外，上述实验中所用的试样在液氮温度下冷却时均未发生相变。因此，制备具有较低氧化钇含量的试样用于Ms和As温度测量。As=1459- 269 Yfor 0 &lt;Y&lt;3 Ms =1279- 364 Yfor 0 &lt;Y&lt;1.5由于2 Y的Ms低于77 K，当Y含量超过2mol%时，用As-Ms测量的驱动力迅速增加。这是不可能解释的自由能的变化或硬度增加，随着Y含量的增加。进一步的研究是必要的，以解释这种急剧变化的Ms温度。

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.