冷却速度对热压ZrO_2（2mol％Y_2O_3）陶瓷中t→m转变的影响

EFFECT OF COOLING RATE ON TETRAGONAL (t) TO MONOCLINIC (m) TRANSITION IN HOT PRESSED ZrO_2(Zmol%Y_2O_3 CERAMIC

利用热膨胀方法，研究了冷却速度对热压烧结的ＺｒＯ２陶瓷（含２ｍｏｌ％Ｙ２Ｏ３稳定剂）正方相（ｔ）到单斜相（ｍ）转变的影响．结果表明：冷却速度可以改变ｔ－ＺｒＯ２相含量，这与ｔ→ｍ转变受热激活控制有关．随冷却速度增加相变开始Ｍｓ下降，结束点Ｍｆ上升．ＴＥＭ观察表明ｍ相的长大速度较钢铁中马氏体慢得多．电子束照射下诱发ｍ相生长说明新相长大必须越过一个能垒．

The effeCt of cooling rate on transition from tetragonal (t) to monoclinic (m) structure in zirconia stabilized with Zmol% yttria is investigated by means of thermal expansion analysis and X-raydiffraction. Experimental results show that the volume fraction of t phase is greatly dependent on the coolingrate, the larger the cooling rate, the smaller the volume' fraction of t phase. The t→m transformation can be completely inhibited when the cooling rate of 100℃ / min is employed. Moreover, the transformation point of t→m and t→m is affected by cooling and heating rate, respectively . The starting point of t→m transformation (Ms) decreases with increasing cooling rate, the ending POint (Mf) increases with increasing colting rate.Both the starting point (As) and ending point (Af) of m→t transformation increases with increasing heating rate. The deviation between the thermal expansion data and X-ray diffraction is also analysed. Present results further demonstrate that the production of m phase in ZrO2 (2mol%Y2O2) is obviously time-dependent and associated with the process of thermal activation. The compound composed of oxygen vacancy and oxygen ion might be responsible for the short-range diffusion. In situ observation of the growing speed of m phase reveals that the growing speed is highly anisotropic, the growing speed along the transverse direction equals 0. 1μm / s and there exists an energy barrier for growth which should be overcomed. (Correspondent:ZHU Welzhong, Department of Metallic Science and Technology, Harbin Institute of Technology,Harbinl 50006)