The Microstructural Analysis of the Effect of Fic on Gas Turbine Blades

Abstract

Advancements in superalloys permit hot gas path components to operate for many thousands of hours under severe centrifugal, thermal and vibratory stresses. The blade of a gas turbine must withstand the most severe combination of temperature, stress, and environment. After a certain period of operation, the blade is damaged by the turbine operation mode. To recover the similar initial mechanical properties, the blade of nickel-based superalloy component undergoes a replacement repair process. A fluoride ion cleaning (FIC) process is used to assist in the successful welding repair of nickel-based superalloy components. This work is to study the FIC influence on a gas turbine blade that was serviced 25,748 equivalent operating hour (EOH) after first overhaul. The blades, including the fractured regions were obtained from a plant. The conditions of blade samples were observed by optical microscope and SEM, and the chemical composition of the flaws in the blade was investigated by EDS. γ′ phase morphology is also an important indicator of the mechanical properties of blades at the high temperatures. The blade condition was examined from morphology and size of the γ′ phase, because the γ′ phase coarsening rate depends largely on the exposure time and temperature.

Second Stage Gas Turbine Blade Premature Replacement Investigation

“…The effect of long-term thermal exposure on the microstructure and the stress rupture property of a directionally solidified nickel-base superalloy [4] shows that the metal carbides coarsens, and the content of Nb in the carbide increases with the rise of the aging time, as do the c 0 size and c 0 phase rafts. In the recent study to recover severely damaged GTD-111DS turbine blades affected by thermal fatigue crack [5], welding repair was successfully used. However, various pre-treatment and post treatment steps were needed to improve the quality of the repaired product.…”