Thermal Shock Damage Characterization of High Temperature Ceramics by Non Destructive Test Methods

The knowledge of the thermal shock resistance of refractory materials is of outmost importance since it determines their performance in many applications, from ceramic manufacturing to oil refinery, thermal insulation, nuclear power, chemical and petrochemical industries. Thermal shock resistance is measured in terms of the number of cycles that a refractory material can withstand when subjected to sudden temperature changes [1]. When refractory materials are subjected to the rapid temperature changes crack nucleation and/or propagation occurs resulting in loss of strength and material degradation. The formation of cracks decreases the velocity of ultrasonic pulses traveling in the refractory because it depends on the density and elastic properties of the material [1-4]. Therefore measuring either of these properties can directly monitor the development of thermal shock damage level. Ultrasonic pulse velocity testing (UPVT) was first reported being used on refractory materials in the late 1950's [2]. Various publications have dealt with the practical application of UPVT to characterize and monitor the properties of industrial refractory materials nondestructively [3-8]. The UPVT method has been considered in detail in ref. [2]. Briefly, pulses of longitudinal elastic stress waves are generated by an electro-acoustical transducer that is held in direct contact with the surface of the refractory under test. After traveling through the material, the pulses are received and converted into electrical energy by a second transducer. It is important to develop an appropriate test methodology to determine accurately the damage propagation in refractory materials required for component life prediction. The main objective of this work was the demonstration of good thermal shock resistance of the used cordirete/SiC composite material and to demonstrate the capability of the ultrasonic velocity technique and image analysis for simple and reliable non-destructive characterization of thermal shock damage.