Fatigue of AM TiAl6V4: Benchmark of defect criticality models

Internal defects in laser powder bed fusion (PBF-LB/M) components are the primary drivers of fatigue failure, yet no systematic comparison of defect criticality models exists for ranking detected defects by severity. This work addresses two complementary research questions: (i) which defect is most critical? and (ii) what fatigue-life does the critical defect imply? For the first question, nine defect criticality ranking models, grouped into three geometry-based approaches (size ranking, Murakami Area model, Tammas-Williams model) and six simulation-based approaches (stress–strain concentration factor, averaged strain energy density, relative stress gradient, Smith-Watson-Topper parameter, equivalent plastic strain, Theory of Critical Distances), are benchmarked on two series of PBF-LB/M TiAl6V4 specimens (93 fatigue-tested; 84 of these inspected by X-ray CT prior to testing; 73 fractographically analysed after testing). The simulation-based models are evaluated with both a linear-elastic and an elastic–plastic material model. A matching procedure links CT defect data to fractographically identified fracture origins (21 of 84 CT-inspected specimens matched). For the second question, three crack growth models (Hartman-Schijve, Murakami-Endo, and a novel hybrid formulation) are compared for fatigue-life prediction based on the identified critical defect. Results show that geometry-based models achieve comparable ranking accuracy to computationally expensive simulation-based approaches, and that distinguishing between internal and surface crack growth environments is essential for accurate life prediction.