Non-Destructive Characterization of Thermal Cycling-Induced Microstructural Changes in Ceramics and Ceramic Matrix Composites

This paper summarizes recent research by the authors on the relationship between internal damping and microstructural alterations of silicon nitride based ceramics and ceramic composites under repeated thermal cycling. The research began from a discovery while studying the damping behavior of the materials as a function of temperature under a thermal cycling environment. The research shows that the damping of samples decreases, accompanied by increases of sample stiffness, after each thermal cycle from room temperature to 1100°C and back to room temperature. The X-ray diffraction (XRD) technique and the impulse-frequency response technique were used to quantify the reasons behind the reduction in material damping capacity and the corresponding increase in stiffness. The comparison of the XRD spectra of the “unheated” and the “heated” samples shows that the glassy phases in the silicon nitride were crystallized during thermal cycling. The result of the research provides evidence that monitoring of material damping can be used as a non-destructive means to characterize the microstructural alterations resulting from environment changes.