Failure Evaluation of a SiC/SiC Ceramic Matrix Composite During In-Situ Loading Using Micro X-ray Computed Tomography

Area of Science:

• Materials Science
• Ceramic Matrix Composites
• Mechanical Engineering

Background:

• Silicon carbide fiber-reinforced silicon carbide matrix composites (SiC/SiC) are advanced materials.
• Understanding their mechanical behavior under tensile load is crucial for applications.
• Existing models for crack propagation and fiber pull-out may not fully capture complex behaviors.

Purpose of the Study:

• To investigate the crack propagation and fiber pull-out mechanisms in SiC/SiC composites.
• To analyze the influence of tensile loading on crack initiation and propagation.
• To explore the effect of heat treatment and oxidation on SiC/SiC composite behavior.

Main Methods:

• Tensile testing of SiC/SiC composite samples.
• In-situ micro X-ray computed tomography imaging during tensile loading.
• Microstructural analysis of pristine and post heat-treated samples.

Main Results:

• Observed expected crack slowing mechanisms and varying resistance to crack propagation based on fiber orientation.
• Identified crack initiation sites including surface flaws and silicon inclusions.
• Post heat-treated samples exhibited significantly longer fiber pull-out than pristine samples.
• Evidence of oxidation was detected in heat-treated samples.

Conclusions:

• The observed long fiber pull-out in heat-treated SiC/SiC is likely influenced by oxidation or oxidation-assisted boron nitride phase transformation.
• Oxidation plays a critical role in the mechanical performance of SiC/SiC composites.
• Oxidation-resistant coatings are necessary for SiC/SiC to ensure long-term durability and performance.