The fatigue crack propagation threshold DELTAK(T) has been determined for two Ti turbine-disk materials. Alloy A is used in many turbines and can be considered as a successful structural material. Alloy N is a new development for applications at higher temperatures. The test results show that the two Ti alloys are practically identical in respect to the non-propagation condition DELTAK(th) as well as the material property DELTAK(T). However, threshold test results show that Alloy N has an extremely low limit for crack propagation under static loading at room temperature, at a stress intensity factor of 700 MPa mm1/2 (24 MPa mm1/2). While Alloy N appears to fulfil the requirements at the desired high end of the temperature range, problems occur in the temperature range below 100-degrees-C. In this lower temperature range, Alloy N tends in its crack growth behaviour more towards ceramic materials than to metallic materials.
