Imperfections in Inner Cavity of Row 4 Turbine Blade Caused by Metal-Core Reaction

Abstract

Abstract When selecting case studies for presentation in this section Failure Analysis of Practical Metallography, the authors of this contribution asked themselves time and again what conditions actually constitute a component failure. Conventional wisdom has it that a failure occurred when a component or assembly lost its function intended by design. The authors readily admit that this is decidedly not the case for the “failure” presented in this contribution. Not only did no failure occur (the component was successfully used in engine service for the intended operating time), but the subject turbine blade did not loose its intended function by any stretch of the imagination. Why is this case study then presented here anyway? Because the evaluation and assessment of severity of indications found upon non-de structive testing of the subject turbine blade was only possible after destructive metallurgical investigation. One could jokingly concede that the blade definitely lost its function after metallographic cut-up. In any case, in the “failure case” presented in this contribution, the engineering department did not dare to release the subject turbine component for renewed engine service after refurbishment, since indications were detected that could not be properly assessed, without destroying the part; hence the subject component was not fit for engine service. The inclined reader may himself decide whether this fact makes it a component failure.