氮化硅陶瓷高温蠕变行为及Y_2O_3和CeO_2的影响

High Temperature Creep Behavior of Si_3N_4 Ceramics and Effect of Y_2O_3 and CeO_2

通过对材料高温下三点弯曲试样中心挠度与时间关系的分析,给出了通过挠度来表征材料高温蠕变性能的方法和表达式,并实际分析了3种不同添加剂氮化硅材料的高温蠕变性能。指出以Y2O3,CeO2为添加剂的氮化硅陶瓷经过热处理后比以MgO为添加剂的氮化硅陶瓷具有更好的抗高温蠕变性能。这主要是由于前者热处理后在晶界析出二次小晶粒,使晶界玻璃相大为减少,有效地抑制了高温下晶界的滑移。此外,Y,Ce与Si,N,O形成的玻璃相高温粘度高,也对材料抗高温变形有利。材料高温下往往是因为变形超过允许极限而失效。此时,通过挠度-时间关系可以很好地反映这一变化过程,并可初步判断材料使用的上限温度。

The relationship for central deflection of specimen with time was studied by means of a testing of threepoint bending at high temperatures. The method and formula, which is used for expressing high temperature creep behavior of materials with change of deflection, were given and the high temperature creep properties of three kinds of real materials, the silicon nitride materials with different additives, were analyzed. The results indicate that the high temperature creep properties of the silicon nitride ceramics doped Y2O3, CeO2 are better than that of the silicon nitride ceramics doped with MgO, after a heat treatment at 1400 ℃. The reasons are that secondary crystallites are formed at grain boundaries of silicon nitride with Y2O3, CeO2 after heat treatment, which decreases the amount of glass phase and restrains grain boundary glide at high temperature. Furthermore, a higher viscosity may be observing in the glass phase consisting of Y, Ce and Si, N, O, which is helpful to improve high temperature creep resistance. Sometimes materials fail due to deforming over the limit. In this respect, the change process can be directly observed by the relationship between deflection and time and the upper limit of service temperature of materials may be estimated roughly.