Metallurgical Analysis Procedure
The techniques used for life analysis are well established in literature and practice. One blade, which is either repre- sentative of the set or exhibits independent, unrepairable damage (such as impact damage), is selected for destructive examination. The initial steps include review of the blade history, visual examination, non-destructive testing, and gathering of relevant surface deposits.
The blade is typically sectioned to remove samples from the lower, mid and upper portions of the airfoil, the tip or shroud and any other features of interest. As the oper- ating temperature of the root is below that at which material degradation occurs, a section of the root is examined to provide a pre-service material benchmark. The samples are prepared for microscopic examination by conventional metallographic polishing techniques
The evaluation includes assessment of the base alloy microstructure, the coating/external surface condition, and the internal surface condition. Modes of degradation can be identified through various forms of microscopy and micro- analysis techniques. Depending on the size/design of the component, mechanical testing of the base metal may also be performed.