Intermetallic g-titanium aluminides (TiAl) offer enormous potential for weight reduction in structural components for elevated temperature applications up to about 750°C due to high specific strength, creep and oxidation resistance combined with a low density of about 4 g/cm³. The substitution of heavier Ni-base superalloys in automotive and aircraft engine components, e.g. turbo charger-wheels or turbine blades improves engine performance and reduces fuel consumption and CO2 emissions. A disadvantage of this material class however, is the low ductility and fracture toughness. In addition to high-cyclic loading, hot gas corrosion and creep, aircraft turbine blades are exposed to the impact of external objects or particles from previous engine stages. Sufficient component safety and damage tolerance can only be ensured by a balanced property profile of the material. In the course of extensive ballistic experiments on preloaded plate specimens, the impact robustness of three TiAl alloys and ten microstructures was determined. Depending on specimen thickness, projectile diameter and material, the lowest impact energy required for crack initiation was determined, as well as the kinetic energy at which specimen fracture occurs under preload. Representative for the loading of a turbine blade by the takeoff/landing cycles, the residual fatigue strength was determined by a step test procedure. The backside cracks were characterized in optical microscopy and computed tomography (CT) studies. Comprehensive scanning electron microscopic analysis show the influence of local microstructure. Ductility and tensile strength are crucial for the initiation of first backside cracks during a low energy impact. However, further crack propagation and failure of the specimen depends on the fracture toughness of the material. Dynamic fracture toughness experiments were performed on specimens instrumented with strain gauges to exclude inertial effects revealed a slightly increasing fracture toughness with increasing loading rate. Fatigue threshold tests showed a pronounced crack resistance curve (R-curve) behavior of the material. A previous tensile overload significantly increased the slope of the cyclic R-curve. In contrast to ductile materials, however, the long-crack threshold does not increase.
|Translated title of the contribution||Impact behaviour and damage tolerance of selected g-TiAl alloys|
|Award date||30 Jun 2023|
|Publication status||Published - 2023|
Bibliographical noteembargoed until 03-03-2028
- titanium aluminide
- foreign object damage