Failure of refurbished turbine blades in a power station by improper heat treatment

Turbine blades in a power station exposed to a temperature of about 800 °C were refurbished after 40,000 h of operation. However, after only 900 h of service at the same temperature, a number of refurbished blades were fractured. Various electron microscopy techniques as well as computational modeling were used to develop a one-to-one correspondence between microstructure and temperature distribution. Fracture was found to occur by a ductile intergranular mode. Although there was no evidence for overheating during service, the results showed that the blades initially contained γ′ precipitate-free zones alongside grain boundaries, which could accelerate intergranular failure consistent with the observed fracture mode. It was concluded that the blades were damaged by improper heat treatment during refurbishing.