Creep behavior of Pt-aluminide (PtAl) coated directionally solidified Ni-based superalloy CM-247LC after thermal exposure

摘要

The effect of cyclic oxidation on the tensile creep properties of a Pt-aluminide (PtAl) coated directionally solidified Ni-based superalloy (CM-247LC) has been evaluated at 980 ℃/220 MPa. Cyclic oxidation of creep specimens was carried out at 1100 ℃ in air up to 750 h. Creep rate and creep life were found to be adversely affected by thermal exposure/oxidation. The extent of degradation of these properties increased with increase in the duration of thermal exposure/oxidation. Such creep behavior has been correlated with the microstructural changes taking place in the coating such as formation of γ' films/ envelopes at B2 (NiAl) grain boundaries, formation of parallel rafts in the region close to coating-substrate interface and coarsening of γ' precipitates in the substrate superalloy during oxidation. The creep strain, on the other hand, was not significantly affected by oxidation. This can be attributed to the prevention of oxidation induced damage by the presence of the coating.