On the possibility of repairing super-exposed IN792 gas turbine blades

Abstract

The blades in the turbine section of gas turbomachines experience high temperatures and, more importantly, mechanical loading stresses, which lead to blade microstructure degradation during service. Regarding this, one of the most economical techniques is to repair or refurbish these blades rather than replacing them with new ones. In the present work, the feasibility of repairing a stage of as-received super-exposed blades in the fourth stage of the turbine hot section is studied. Several samples are prepared from the as-received blades; afterward, a few samples are rejuvenated with standard heat treatment. Later, for both as-received and rejuvenated samples, metallurgical analysis of microstructure, such as optical microscopy and scanning electron microscopy, is performed. In addition, mechanical tests, such as high-temperature and room-temperature tensile tests, creep tests, and their fractography, are conducted. Finally, the results associated with both rejuvenated and as-received samples are compared with the minimum standard criteria provided by the original equipment manufacturer (OEM). It has been shown that the microstructure and mechanical properties of the as-received samples indicate that the blade is fully retired. Later, using the rejuvenation technique, the microstructure and mechanical behavior of the blades are restored not completely but favorably (around 30% recovery), and the lifetime of the rejuvenated blades can be extended for another working sequence.