Effect of cavitation caused by superplastic deformations on thermal shock properties in ceramics

超塑性变形引起的空化对陶瓷热震性能的影响

基本信息

批准号：
13650752
负责人：
MOTOHASHI Yoshinobu
金额：
$ 1.41万
依托单位：
IBARAKI UNIVERSITY
依托单位国家：
日本
项目类别：
Grant-in-Aid for Scientific Research (C)
财政年份：
2001
资助国家：
日本
起止时间：
2001 至 2002
项目状态：
已结题

来源：
https://kaken.nii.ac.jp/grant/KAKENHI-PROJECT-13650752/
关键词：
superplasticity ceramics Y-TZP cavitation thermal shock 臨界温度差 3Y-TZP HIP 熱応力

项目摘要

Superplastic deformations of ceramics frequently cause various microstructural evolution such as formation and growth of cavities at grain boundaries, concurrent grain growth, variation in grain aspect ratio and so on. It has been reported that the cavities formed in 3Y-TZP owing to superplastic deformations deteriorate hardness and bending strength of the material, while they improve its fracture toughness to some extent. Another important factor to be examined must be thermal shock behavior. In this work, the effect of cavities on thermal shock resistance of the 3Y-TZP was investigated by an indentation-quenching method. Parts of the superplastically-deformed 3Y-TZP specimens were subjected to hot-isostastic-pressing (HIP) to reduce the amount of cavities to zero. The thermal shock tests were then carried out on both of the as-deformed and HIP'ed specimens to separate the effect of cavities from other factors. The main results obtained are as follows :(1) The critical temperature difference (△T_c) is in proportion to l^<-1/2>, as is predicted from the Hasselman's equation, where l is the initial surface crack half-length.(2) The △T_c is improved as the volume fraction of cavities (V_c) is increased. It appears that the following is responsible for this result : The apparent thermal expansion coefficient of the 3Y-TZP was probably reduced with the increase in V_c under such a condition that thermal stresses are arising upon quenching which led to the enhancement in △T_c.(3) The △T_c, showed au upper limit at approximately 210 K within the present experimental range. It seems that this was caused by the acceleration of the degradation at the precrack up region where concentrated thermal stresses would arise with aqueous environment at around 483 K in a very beginning stage of the quenching process.

陶瓷的超塑性变形经常引起各种微观结构的演变，例如晶界处空腔的形成和生长、同时晶粒生长、晶粒长宽比的变化等。据报道，由于超塑性变形而在3Y-TZP中形成的空腔恶化。材料的硬度和弯曲强度，同时在一定程度上提高了材料的断裂韧性。在这项工作中，必须检查空腔对热冲击性能的影响。通过压痕淬火方法对部分超塑性变形 3Y-TZP 样品进行热等静压 (HIP)，以将空腔数量减少到零，然后进行热冲击试验。对变形和热等静压试样进行分析，将空腔的影响与其他因素分开，得到的主要结果如下：(1)临界温差。 (△T_c) 与 l^<-1/2> 成正比，根据哈塞尔曼方程预测，其中 l 是初始表面裂纹半长。 (2) △T_c 随着空腔体积分数的增加而提高(V_c) 增加似乎是以下原因造成的：在产生热应力的情况下，3Y-TZP 的表观热膨胀系数可能随着 V_c 的增加而减小。 (3)在目前的实验范围内，ΔT_c的上限约为210 K，这似乎是由于预裂纹集中区域的退化加速造成的。在淬火过程的最初阶段，在 483 K 左右的水环境中会产生热应力。