Failure due to structural degradation in turbine blades

During test run, tips of two high pressure turbine blades of an engine were found chipped off. The material of the blades is Udimet 500 and blades are used without any additional coating. The cause of failure is found to be intergranular crack(s) which started during exposure to high temperature. The phenomenon occurred at the pressure as well as the suction sides and the regions close to the tip experienced high distress. Cracks initiated from the oxidized/corroded grain boundaries and propagated to the critical length to result in catastrophic fracture. An indication of the blades running hot is the microstructural degradation. The mechanism of failure was hot corrosion followed by high cycle fatigue.