Pyrolytic carbon indentation crack morphology

Area of Science:

• Materials Science
• Fracture Mechanics
• Surface Engineering

Background:

• Vickers indentation cracks are commonly used to study fatigue and fracture in brittle materials.
• Standard models like radial-median and Palmqvist cracks are often applied to analyze indentation-induced fracture.
• The specific crack morphology in pyrolytic carbon coatings on graphite substrates remains undescribed.

Purpose of the Study:

• To characterize the true morphology of Vickers diamond and spherical ball indentation cracks in pyrolytic carbon coatings.
• To compare the observed crack systems with established radial-median and Palmqvist models.
• To assess the implications of unique crack morphologies on fracture mechanics analysis.

Main Methods:

• Utilized serial metallographic cross-sections to examine crack propagation.
• Employed indentation fracture in bending tests to induce and analyze cracks.
• Incorporated acoustic emission and residual surface indentation scanning for comprehensive characterization.

Main Results:

• Indentation crack systems in pyrolytic carbon coatings did not conform to typical radial-median or Palmqvist models.
• A unique crack morphology was observed, potentially influenced by coating thickness limitations.
• Significant deviations from standard crack models were documented.

Conclusions:

• The fracture behavior of pyrolytic carbon coatings under indentation is distinct and material-specific.
• Standard indentation crack equations may not be suitable for analyzing fracture mechanics in these coatings.
• Further research is needed to develop appropriate models for small crack growth in such materials.