Investigation of the Fracture Behavior of cBN-Glass Composites
Open Access
- Author:
- Mendoza, Alfonso Julio
- Graduate Program:
- Materials Science and Engineering
- Degree:
- Master of Science
- Document Type:
- Master Thesis
- Date of Defense:
- None
- Committee Members:
- Carlo G Pantano, Thesis Advisor/Co-Advisor
David John Green, Thesis Advisor/Co-Advisor
Michael Anthony Hickner, Dissertation Advisor/Co-Advisor - Keywords:
- cBN
fracture behavior
mechanical properties
digital image analysis
SEM - Abstract:
- Samples of cBN-borosilicate composites were synthesized and mechanically failed to create fracture surfaces for characterization of the crack propagation. The cBN crystals were also oxidized to determine differences in fracture toughness and crack propagation due to modification of the cBN-glass interface. The diametral compression test, using a single-edge V-notch, was employed to measure the fracture toughness and create the fracture surfaces for study. This test is attractive because it can be used for brittle materials without loading or gripping difficulties, and the notch is relatively easy to machine into the samples. The fracture toughness for borosilicate glass was found to be 0.56MPam. Toughness increased with increasing volume fraction up to 40vol% to a value of 1.41MPam for a 40vol% cBN composite, an overall increase of 152%. The addition of oxidized cBN increased the fracture toughness to 1.28MPam for a 40vol% oxidized cBN composite, an overall increase of 129% from the borosilicate glass. SEM images were taken of the fracture surfaces to characterize the crack path through these composites. Two types of direct interactions between the crack and embedded particles were identified based on matched image pairs of the fracture surfaces: transgranular particle failure and interfacial failure. Digital image analysis and SEM images were used to quantify the areal density of cBN on the fracture surfaces to determine the frequency of crack particle interaction with the cBN crystals. It was found that for the cBN-borosilicate glass composite, where the CTEcBN > CTEglass, the crack preferentially propagates through the glass matrix due to local compressive stresses surrounding the cBN crystal.