Fracture Mechanics Characterization of Rotating Anode Components

Rotating anodes in X-ray tubes are subjected to extreme thermal stresses, necessitating preconditioning that induces a network of surface cracks. This study investigates the fracture toughness and fracture mode transitions of two tungsten-rhenium focal track materials at ¿196 °C, room temperature, and 500 °C. A modern vacuum plasma-sprayed (VPS) material is compared to the conventional sintered and forged (PM) variant. The VPS material exhibits an elongated grain morphology designed to minimize dose loss over the anode¿s service life. However, this microstructure may compromise fracture toughness, due to the known grain morphology dependence in tungsten-rhenium alloys. Small-scale samples extracted from manufactured anodes, reflecting in-service microstructures, were tested to quantify fracture toughness. Measured in the axial direction at 500 °C, the critical stress intensity factors ranged from 20.0 - 23.2 MPa¿m for VPS and 17.5 - 19.9 MPa¿m for PM, demonstrating that VPS achieves values comparable to PM. A clear fracture mode transition was observed in both materials, shifting from cleavage at low temperatures to intercrystalline fracture at high temperatures. To investigate crack-tip behavior at the interface to the base body, composite beam samples were designed, and stress intensity factors were calculated using a Green¿s functions-based model. These results underscore the utility of miniaturized sample testing for evaluating the fracture mechanics of anode components.