Identification of failure mechanisms in nickel base superalloy turbine blades through microstructural study

Failures in gas turbine blades can occur by various mechanisms that are operative at high temperatures. Most frequent ones are the creep and stress rupture. These mechanisms are strongly dependent on the microstructure of the blades and often, they are facilitated due to microstructural degradation that occurs during service exploitation. The study of these failures, therefore, requires detailed microstructural examination. This paper reports the basic microstructural features in cast nickel base superalloys that control the failure mechanisms in gas turbine blades followed by analysis of two service failures. A methodology has been suggested for effective microstructural analysis of turbine blades after service exposure. It has been shown how systematic microstructural study on the turbine blades can be helpful in establishing engine operating conditions.