Fracture tests of microsized TiAl specimens

ABSTRACT γ‐TiAl‐based materials have the ability to provide superior creep strength, high yield strength and Young's modulus at temperatures as high as 700 °C. This has led to the consideration of γ‐TiAl‐based materials for use in microelectromechanical systems (MEMS) intended for application at elevated temperatures. One γ‐TiAl‐based material under consideration for these applications is the composition known as Alloy 7/Ti–46Al–5Nb–1W (at%). In this case, this material is tested in the as‐wrought form with a fully lamellar structure and a colony size ≈75 μm. The effect of loading volumes of this material smaller than conventional samples is investigated. This is carried out in order to improve understanding of the fracture toughness behaviour, which ultimately will be required of components of this material with a cross‐section ≈18 × 6 μm. Here, we focus upon a specially developed machine, which provides accurate loading of microsized cantilever beams through a diamond tip. The directional nature of the fracture toughness properties of this material is considered in relation to the local orientation of the lamellar microstructure and the resulting failure modes occurring.