Oxidation-controlled creep response of miniaturized Waspaloy specimens in a hydrogen-containing atmosphere

• Miniaturized Waspaloy creep specimens are highly sensitive to oxidation-induced surface degradation. • At 875 °C, differences in creep softening are closely related to differences in oxidation behavior. • Ar + 5 % H 2 produces a thinner and more homogeneous oxide scale than Ar. • Slower oxidation in Ar + 5 % H 2 delays degradation of the effective load-bearing cross section. • A direct hydrogen effect on the creep mechanism could not be conclusively isolated. Hydrogen-containing atmospheres are of growing interest for high-temperature applications, but their influence on the creep behavior of Ni-based superalloys remains difficult to assess under realistic conditions. In this study, the creep response of Waspaloy was investigated using miniaturized tensile specimens and related to oxidation behavior in Ar and Ar + 5 % H 2 atmospheres. The applicability of the miniaturized creep approach was first assessed by comparison with conventional macroscopic specimens. At 925 °C and 120 MPa, macro and micro specimens showed broadly similar creep behavior during the short test durations, indicating that surface-related degradation did not dominate the overall response. At 875 °C and 80 MPa, the minimum creep rates remained similar in both atmospheres, whereas subsequent creep softening was delayed in Ar + 5 % H 2 . Complementary oxidation experiments at 875 °C revealed a thicker, more heterogeneous oxide scale with stronger internal oxidation in Ar, while Ar + 5 % H 2 produced a thinner, more homogeneous oxide scale. These results show that the creep response of miniaturized specimens is strongly influenced by oxidation-induced surface degradation and the resulting reduction of the effective load-bearing cross section. A direct hydrogen effect on the high-temperature creep mechanism could not be conclusively identified.