Isothermal LCF behavior in aluminide diffusion coated René 80 near the DBTT

Ni-base superalloys such as René 80 are widely used for aircraft turbine blades manufacture, due to possesses suitable mechanical, oxidation and hot corrosion properties. It is usually coated in order to increase its wear, oxidation, erosion and hot corrosion properties against environmental degradation. One the most important properties of coatings is its DBTT. In this paper the behavior of uncoated and coated (CODEP-B) René 80 has been studied near the DBTT (871 °C), R = (εmin/εmax) = 0 and strain rate of about 2 × 10−3 s−1. Experimental results show that in coated specimens while the total cyclic strain is lower than 1%, coating leaves longer fatigue life, at this condition the nucleation of the cracks occurs merely in substrate, but in strains more than 1% as a result of nucleation of cracks in the coating surface, diffusion layer and substrate simultaneously, fatigue life time of the coated specimens is lower than that of uncoated specimens.