Influence of microstructural architecture on the fracture resistance of W Re focal tracks

Rotating anodes in X-ray tubes are subjected to extreme thermal stresses, necessitating preconditioning that induces a network of surface cracks. As such, the necessity of fracture mechanical tools in their engineering is evident. Challenges are posed by the strong morphological dependence of fracture mechanical properties in typically used tungsten‑rhenium alloys, as well as the limited thickness of focal tracks. In the experimental evaluation of toughness parameters, samples must be taken directly from a routinely manufactured rotating anode, to ensure a comparable microstructure. In this contribution, small-scale samples are designed and extracted from focal track material to measure its local fracture resistance in a temperature range between −196 °C and 500 °C for two material systems. An advanced vacuum plasma-sprayed (VPS) material, exhibiting an elongated grain morphology, is compared to the conventional sintered and forged (PM) variant. Measured in the axial direction at 500 °C, the critical stress intensity factors range 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, despite the pronounced difference in the investigated microstructures. Additionally, composite beam samples were designed to study the crack tip-interface interaction, and stress intensity factors for the composite beam case were deduced using a Green's functions approach. Plasticity and residual stress influences were estimated using a finite element model. • Small-scale samples are designed and produced from rotating anode focal tracks. • Elongated grain morphology of VPS - W Re10 does not reduce fracture toughness. • Stress intensity factors for composite samples are evaluated and compared. • Influences of residual stresses and plasticity at the interface are evaluated.