Study on Stress-Induced Phase Transformation of Rare Earth Aluminates
| Project/Area Number |
07455262
|
|---|
| Research Category |
Grant-in-Aid for Scientific Research (B)
|
| Allocation Type | Single-year Grants |
|---|
| Section | 一般 |
|---|
| Research Field |
Inorganic materials/Physical properties
|
|---|
| Research Institution | TOHOKU UNIVERSITY |
|---|
Principal Investigator |
SHIMADA Masahiko Tohoku University, Institute for Advanced Materials Processing, Professor, 素材工学研究所, 教授 (80029701)
|
|---|
| Co-Investigator(Kenkyū-buntansha) |
ENDO Tadashi Tohoku University, Faculty of Engineering, Professor, 工学部, 教授 (30176797)
TAKIZAWA Hirotsugu Tohoku University, Faculty of Engineering, Associate Professor, 工学部, 助教授 (90226960)
UCHIDA Satoshi Tohoku University, Institute for Chemical Reaction, Research Associate, 反応化学研究所, 助手 (60232849)
YAMANE Hisanori Tohoku University, Institute for Advanced Materials Processing, Associate Profes, 素材工学研究所, 助教授 (20191364)
|
|---|
| Project Period (FY) |
1995 – 1996
|
| Project Status |
Completed (Fiscal Year 1996)
|
| Budget Amount *help |
¥7,600,000 (Direct Cost: ¥7,600,000)
Fiscal Year 1996: ¥800,000 (Direct Cost: ¥800,000)
Fiscal Year 1995: ¥6,800,000 (Direct Cost: ¥6,800,000)
|
|---|
| Keywords | Rare earth aluminate / Phase transformation / High temperature fracture strength / Ceramic composite / Metastable orthorhombic phase / High temperature monoclinic phase / 温度誘起相転移 / 高温単斜相 / 斜方晶準安定化 / 粒径依存結晶相 / 応力誘起相転移 |
|---|
| Research Abstract |
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
|
Report
(3 results)
Research Products
(6 results)
