Experimental evaluation and phase-field modelling of bulk and interface fracture toughness in residually stressed TiN-FeCr films

Understanding and evaluating the fracture behaviour of micro-architected multilayer systems is essential to ensure structural integrity. This work proposes a novel hybrid experimental–computational framework to characterise the fracture toughness of coatings at the micrometre scale.Pre-notched micro-cantilever tests were performed on TiN-coated FeCr specimens fabricated by focused ion beam machining. The tests provided load–displacement curves and direct observations of crack propagation within the TiN layer and subsequent TiN–FeCr interface delamination. Residual stresses resulting from the TiN deposition were quantified experimentally and incorporated into the simulations through an eigenstrain-based approach, enabling the representation of deposition-induced stresses, their redistribution during micro-cantilever fabrication, and their role in crack initiation and growth.A generalised cohesive phase-field model was developed and validated against the experiments to capture the two key fracturing processes involved. The TiN layer was described by an orthotropic phase-field formulation to represent its anisotropic fracture response, while the FeCr substrate was modelled as an elastoplastic material.The proposed methodology successfully reproduces the experimental fracture sequences and allows the intrinsic toughness of the TiN layer to be distinguished from the effects of residual stress. Furthermore, it enables a consistent identification of the TiN–FeCr interfacial decohesion properties, accounting for substrate plasticity. The successful application of the proposed approach opens new avenues for advanced structural assessments of coated microstructures and thin-film systems, widely found in advanced engineering applications, and provides a general pathway to incorporate eigenstrain-based residual stress fields, anisotropic fracture, and elastoplastic substrate effects in phase-field analyses of micro components.