Behavior of a Next-Generation Nickel Super Alloy Turbine Component under Direct Exposure to Gas Heat from Combustion in a Long-term Operation

In this research, the microstructural evolution and creep behavior of a second-stage vane from a gas turbine after 1200 long-term cycles were evaluated through microstructural examinations and creep tests. Microscopic analyses revealed an increase in the volume fraction and size of secondary phases such as gamma prime and carbides. These microstructural changes led to the embrittlement of the investigated nickel superalloy. Hardness testing results indicated an increase in hardness from 420 Vickers to 480 Vickers for the service-exposed vane after direct exposure to gas heat. Thermal analysis showed a 60°C decrease in the complete dissolution temperature, suggesting a need for repair or rejuvenation of the alloy. The growth of gamma prime precipitates through the shearing of dislocations and the coarsening of carbides due to the inhibition of grain boundary sliding resulted in an 11-hour reduction in creep life. The reference sample failed at a stress of 247 MPa and a temperature of 900°C after 40 hours with a strain of 9%. In contrast, the service-exposed vane exhibited a reduction in creep life and creep strain to 29 hours and 4%, respectively.