Premature failure of turbine blades in the combustion zone was reported in one of the aeroengines. The engine had compressor turbine and free turbine in a common shaft. When the failure occurred, the power of the compressor came down to less than 2 percent of its value, after 2100 hrs of service. Stripout examination of the engine revealed complete failure of the shroud tips of the turbine blades in the first and second stages of the turbine and partial melting of many thermocouple assemblies. Detailed failure analysis on the failed blades revealed presence of creep cavities. Protective coating had also peeled off at many locations giving way for enhanced creep strain due to direct overtemperature exposure.In another case, failure of turbine blades was detected in another aeroengine, which was operating in a coastal environment. In this failure, the protective coating on the blades was found to have cracked at many locations and also revealed grain boundary spikes. The matrix was found to contain wedge type creep cavities and grain boundary cracking. Discrete particles were found to be present in the matrix depleted zone adjacent to the base metal. The cause of this failure is established to be hot corrosion followed by creep damage.Systematic failure investigations carried out to establish the root cause of the failure of the blades in these two aeroengine the remedial measures recommended to avoid recurrence of such failures are discussed in this paper.
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