Structural degradation and elemental variations in an ex-service first-stage gas turbine blade

Microstructure degradation and residual low cycle fatigue life of a serviced turbine blade

“…The degradation of γ′ precipitate at 50 % and 70 % airfoil spans is pronounced. This phenomenon has also been observed in the other turbine blades of the serviced aero‐engine 16 and the gas turbine engine 19 . It is well recognized that the coarsening of γ′ precipitate in the Ni‐based superalloy is mainly dependent on the exposure temperature but hardly affected by the stress 9 .…”

“…However, the morphology and size of γ 0 precipitate in the airfoil were obviously distinct in two blades. Coarsened and rafted γ 0 precipitate were also observed in the directionally solidified 16 and single crystal 19 turbine blades. The degradation of γ/γ 0 phases at different spots varies, and the most significant change in its γ 0 precipitate appears in the trailing edge (TE).…”

“…This phenomenon has also been observed in the other turbine blades of the serviced aero-engine 16 and the gas turbine engine. 19 It is well recognized that the coarsening of γ 0 precipitate in the Ni-based superalloy is mainly dependent on the exposure temperature but hardly affected by the stress. 9 It is indicated that the 50-70 % span experiences the relatively high temperature during service.…”

“…This is attributed to the longest high temperature and the fluctuation in the working conditions for the leading edge (LE) compared with other parts 16 . Coarsened γ′ precipitate structures were also observed in the trailing parts 19 …”

“…16 Coarsened γ 0 precipitate structures were also observed in the trailing parts. 19 Generally, turbine blades are typically retired from operation after a defined operational period or based on a lifetime counter, even when there is little or no visible damage. 20 Considerable efforts 16,18,[20][21][22] have been devoted to extending the service life of these components beyond their original design lifespan.…”