Thermal Shock Test of Ceramics by a Helium Gas Cooling Method.

In order to evaluate the reliability of ceramics under transient thermal stresses, a thermal shock test equipment was designed and fabricated. Cylindrical specimens made of Si3N4 and SiC were tested by the test equipment. Each specimen was preheated uniformly at 1573 K in an electric furnace and then it was pulled down rapidly into a cooling chamber beneath the furnace. At the same time, it was cooled locally by high-velocity helium gas passed through a narrow slit. The transient temperature distributions were measured by optical pyrometers and thermo-couples. The moment of the fracture was confirmed by the sound of the fracture itself and fracture originated at the outer surface just under the cooling nozzle. The results showed that Si3N4 Specimens were fractured more severe cooling conditions than that of SiC.