Abstract

The René 77 nickel-based superalloy is used for critical elements such as industrial gas turbine blades. In this case, it is used in the first stage of the GE MS 7000 1B turbine. This type of blade is manufactured using the lost wax casting method, they are high-quality pieces. This work presents the microstructural study of Rene 77 blades, with rejuvenation heat treatment, which, in routine borescopic inspection, after 10,000 hours of service, presented surface cracking. At this stage of the turbine, the blades have a cooling system to preserve their integrity, so it is necessary to study the cracking mechanism present to corroborate whether the remaining ones can continue operating, be recovered or replaced. Several evaluations were carried out, including macroscopic and visual inspection of the outer surface of the blade and microstructural and chemical evaluation by SEM-EDS of samples extracted from the hottest zone, to the coldest zone of the root. The results obtained show a significant degradation that affects the microstructural stability throughout the blade structure. The thickening of the ' phase caused a change in its morphology, which affects the mechanical properties, since the ' phase acts as a barrier to the movement of dislocations, retarding thermo-creep, so the resistance to this mechanism decreased significantly. It is suggested that restoration of microstructure and properties can be effected with appropriate rejuvenation heat treatment.