Study of mechanical degradation and microstructural characterization in a ni-based superalloy component of a gas turbine

The microstructural characterization of a blade made of Ni-based superalloy was carried out and discussed. The blade was removed from service, of a gas turbine, due to preventive maintenance. This component was studied on different cross sections according to the surface temperature obtained by ANSYS software. The cross sections were characterized by Optical Microscopy (OM), Scanning Electron Microscopy (SEM) and High Resolution Scanning Electron Microscopy (HR-SEM). It was determined that the maximum value of total deformation is 0.001717 mm, located in the surface upper section of the blade, which not correspond to the section with the highest value of temperature calculated with ANSYS software. These results were consistent with the rafted microstructure observed at the upper region of the blade. Microcavities close to the MC carbides with a size of about 40x10^-6 m were also observed. The mechanical behavior of the Ni-based superalloy was studied by Rockwell Hardness testing (RHT). So, morphological changes were identified in the occurrence of the strengthening precipitated, γ', according to the operating conditions: stress and temperature. The average radius of the γ' precipitated was obtained by computer image analysis using ImageJ software. No clear relationship was found between the hardness values obtained and the coarsened γ' precipitated. A bimodal occurrence of coarsened γ' particles was identified distributed through γ matrix by HR-SEM. Thus, this study was carried out with the purpose to identify the critical parameters that promote microstructural changes in the Ni-based superalloy and therefore affect the mechanical behavior in this turbine blade.