Influence of the Creep on Microstructure and Mechanical Properties of SiC/SiC Composites

SiC/SiC composites were subjected to creep testing at the temperature of 980 and 1100°C. The specimens were tested at maximum stress levels of 100, 150 and 200 MPa. Their microstructure after creep testing were analyzed using a Scanning Electron Microscope (SEM), and the chemical composition was determined by Energy Dispersive Spectroscopy (EDS) and Electron Spectroscopy methods. To evaluate mechanical degradation, the modulus of elasticity (Young’s modulus) was determined from the stress-strain data during loading and unloading. All tested specimens were not ruptured after 200 hours of creep testing at 100 MPa, regardless of the temperature. However, at 980°C for the stress of 200 MPa creep specimens were ruptured between 33 and 106 hours, while at 1100°C, they were ruptured in less than 1 hour. It was concluded that the stress level of 200 MPa exceeded the fracture strength of the composite matrix. Analysis of the microstructure of the specimens subjected to creep testing at 1100°C revealed a large number of cracks in the matrix material, which facilitated oxygen penetration and ultimately led to the destruction of the matrix material.