We studied the different parts (lock and feather) of Inconel 738C gas turbine blade, which were cut from the working turbine blade after long operation and recovery heat treatment. Undesired phases such as TCP phase (sigma phase) and some of continuous carbides such as M23C6 in the grain boundary are found. The presence of M23C6 carbides in studied samples testifies to the diffusion process of decomposition of MC carbide and the associated softening of the alloy. The appearance of sigma phase leads to embrittlement of the alloy. Generation of these specifications in the structure results in degradation of metallurgical and mechanical properties of the blade and eventually its destruction.