Development of in-situ monitoring system for sintering of ceramics using laser AE technique

Acoustic emission (AE) technique is useful for in-situ detection of micro-fracture in materials. However, a piezoelectric sensor has a limitation in application at elevated temperatures because PZT has Curie point. We have investigated a non-contact AE technique using laser interferometer as a sensor. Cracking in firing of structural ceramics presents serious fabrication problems. Cracks form in the heating, sintering or cooling step of firing, and their initiation is strongly affected by shape, density, particle size and firing pattern. It is important to investigate when cracks occur for the optimization of firing condition. In this study, we firstly developed a non-contact in-situ monitoring system for firing of ceramics. We tried to monitor the cracking in firing of alumina (Al2O3) with the maximum temperature of 1600DGC. A sample was heated in electrical furnace and probe beam was irradiated on surface of SiC disc inserted between the sample and the furnace through small opening. Developed monitoring system could successfully detect cracking in firing. This system can be applied to AE measurement of samples above 1500DGC. It was demonstrated that laser AE system could detect internal cracks, which did not reach to surface of sample in firing process. This means that integrity of sintered ceramics may be ensured based on non-contact AE measurement.