Numerical Simulation of Fracture in Coated Brittle Materials Subjected to Tribo-Contact

Manufacturing processes used to deposit hard coatings often produce cracks which reside within the coating, at the interface, or in the substrate. These cracks originate from material defects and thermal expansion mismatch. When subjected to stress (from solid body contact) the cracks can act as flaws which initiate and/or propagate subsequent fracture contained entirely in the coating, substrate, interface, or combinations thereof. The finite element method has been used in conjunction with a numerical interface fracture mechanics model to investigate the structural response of coated brittle materials subjected to normal and shear loads (tribo-contact). Residual stresses from depositing TiC onto a WC-TiC-TaC-Co substrate were superimposed with loads that simulate a single point scratch test. Experimental observations of metallographic cross sections, taken through scratched TiC films, were used for verification and guidance in modeling. This study has examined how flaw orientation affects crack propagation through the coating, interface, and substrate. The importance of interface fracture toughness and anisotropy in coating mechanical properties are discussed in light of wear particle formation.