Crystal-Structure-Based Modeling Study of Temperature-Dependent Fracture Toughness for Brittle Coating Deposited on Ductile Substrate

The temperature-dependent fracture toughness of a brittle coating/ductile substrate system, WC-10Co4Cr deposited on 1018 low carbon steel, is evaluated at microscopic level using an indentation-based model in terms of the Arrhenius-type equation and rate-controlling theory. The formulation of the model utilizes the parameters of crystal structures of each phase in the coating material. The slip systems of hard hexagonal \( \updelta \)-WC phase and soft FCC \( \upalpha \)-Co phase are analyzed. The fracture toughness of the two-phase coating is obtained by integrating the fracture toughness of single \( \updelta \)-WC phase coating and that of single \( \upalpha \)-Co phase coating using either the basic mixture method or the unconstrained mixture method. The results suggest that the fracture toughness of WC-10Co4Cr coating/1018 low carbon steel substrate system may remain constant until the temperature reaches a critical value, about 200 K, and ranges from 2.16 to 10.82 \( {\text{MPa}}\;{\text{m}}^{1/2} \), with temperature increasing from room temperature (298 K) to 1000 K.