Coating pre-cracking effect on the LCF fatigue life of superalloys for gas turbine blades

In gas turbine engines for aerospace propulsion, the application of coatings on HP and LP stage blading where the highest temperatures are experienced is a common practice to prevent environmental degradation. However, since the strength of the coating is lower than that of the substrate material, upon loading the static strength of the coating may be exceeded and coating cracking may occur. In order to assess the effect of cracking in the coating on polycrystalline nickel superalloy MAR-M002, a number of combined cycle fatigue (CCF) and low cycle fatigue (LCF) tests with and without dwell have been carried out, at temperatures up to 870 °C. Comparison of the CCF and of the LCF tests with dwell with conventional LCF tests is presented herein, with special discussion of the effect of coating cracking.