Study on Stress-Induced Phase Transformation of Rare Earth Aluminates

稀土铝酸盐应力诱导相变研究

基本信息

批准号：
07455262
负责人：
SHIMADA Masahiko
金额：
$ 4.86万
依托单位：
TOHOKU UNIVERSITY
依托单位国家：
日本
项目类别：
Grant-in-Aid for Scientific Research (B)
财政年份：
1995
资助国家：
日本
起止时间：
1995 至 1996
项目状态：
已结题

项目摘要

Transformation toughening is one effective approach to improving the fracture toughness and fracture strength of brittle ceramics. Transformation toughening requires the stress-induced martensitic transformation of particles, as is well known in tetragonal zirconia ceramics. The main purpose of our study is to find new oxide ceramics with stress-induced phase transformation. In the present study, the relationship between orthorhombic and monoclinic phase, the possible factors for metastabilization of orthorthombic phase at room temperature and thermal and mechanical properties in (R_<1-x>La_x)_4Al_2O_9 and Gd_4Al_2O_9/MgO composites are examined. Single phase solid solutions with orthorhombic structure were synthesized by reaction sintering at 1700ﾟC for 30h in air within the composition range of 0*x<0.5 for (Ho_<1-x>La_x)_4Al_2O_9 and 0*x<0.3 for (Gd_<1-x>La_x)_4Al_2O_9 system. Above these composition ranges, perovskite-type LaAlO_3 coexisted as second phase. Metastable orthorhombic p … More hase was capable of quenching to room temperature under the conditions of grain growth above the critical particle size of 6.2mum for x=0, and 3.3mum for x=0.2 in (Ho_<1-x>La_x)_4Al_2O_9 and 2.7mum for x=0 and 2.4mum for x=0.2 in (Gd_<1-x>La_x)_4Al_2O_9. After polishing the surface of all sintered bodies with orthorhombic phase at room temperature, the crystal structure of samples changed to a monoclinic structure ; i.e.a stress-induced phase transformation occurred during the polishing process. This stress-induced phase transformation from orthorthombic to monoclinic structure was accompained by an increase of volume of about 0.5%. From the results of DSC measurements, the thermal phase transformation of Gd_4Al_2O_9 is reversible and has hysteresis. The transition temperature, defined as the average temprarure of exothermic and endothermic peaks, was 1110ﾟC,which correspond to the phase transformation from low temperature monoclinic to high temperature monoclinic structure. On the other hand, a second transition temperature was observed at 1430ﾟC on heating and at 1420ﾟC on cooling, which would correspond to the phase transformation from monoclinic to orthorhombic structure. Less

转化韧性是一种有效的方法，可以改善脆性陶瓷的断裂韧性和断裂强度。转化韧性需要应力引起的颗粒的马塞塞我转化，这在四方氧化锆陶瓷中众所周知。我们研究的主要目的是找到具有应力诱导相变的新氧化陶瓷。在本研究中，正骨和单斜相相之间的关系，在室温下转移正常相的可能因素以及（r_ <1-x> la_x）_4Al_2O_9和GD_4AL_4AL_2O_9/MGO组成中的（r_ <1-x> la_x）中的热和机械性能。通过在1700°C处在1700°C处进行反应烧结在0*x <0.5的空气中，（HO_ <1- x> la_x）_4Al_2O_9和0*x <0.3的单相固体溶液在1700 c <0.5的空气中合成30小时。在这些组成范围之上，钙钛矿型LAALO_3共存为第二阶段。在谷物生长的条件下，X = 0的晶粒生长量高于6.2mum的临界粒径，X = 0.2 = 0.2 in（HO_ <1-x> la_x）_4Al_2O_9和2.4mum x = 0和2.4mum x = 0和2.4mum，x = 0和2.4mum x = 0和2.4mum x = 0和2.4mum x = 0 and x = 0.2 = 0.2 （gd_ <1-x> la_x）_4Al_2O_9。在在室温下抛光所有烧结物体的表面后，样品的晶体结构变为单斜结构。即在抛光过程中发生了应力诱导的相变。这种应力诱导的相位从正常屈服到单斜结构的变化是通过增加约0.5％的增加的。根据DSC测量结果，GD_4AL_2O_9的热相变是可逆的，具有滞后。过渡温度定义为放热和吸热峰的平均温度，为1110 ﾟC，对应于从低温单斜纤维纤维纤维细胞到高温单斜结构的相变。另一方面，在加热时和冷却时在1430 ﾟC处观察到第二个过渡温度，这将与从单斜骨到正骨结构的相变相对。较少的