New insights into tensile creep behavior and early-stage damage in a MoSiBTiC alloy at ultrahigh temperatures

Abstract In this study, the tensile creep behavior of a MoSiBTiC alloy, a promising candidate for ultrahigh-temperature applications, was investigated in the temperature range of 1400–1700 °C and the applied stress range of 100–300 MPa, with a focus on the early stages of deformation. A non-contact method was employed to directly measure gauge length changes in the tensile specimens. The alloy exhibited non-steady-state creep behavior, characterized by a minimum creep rate attained during the transient regime at a true strain of approximately 0.02–0.03, followed by a transition to tertiary creep. Based on the strain of 0.01 (~ 1%), the Larson–Miller parameter was derived, and the temperature required to reach 1% strain under 170 MPa in 125 h was estimated to be approximately 1222 °C. The stress exponent n determined from the Norton plots was on average 3.6 ± 0.2, and the apparent activation energy Q c obtained from the Arrhenius plots was 515 ± 42 kJ mol −1 . A possible change in the deformation mechanism was suggested between 1500 and 1600 °C, necessitating further investigation. Microstructural observations revealed the formation of voids and microcracks in the T 2 phase as early as the initial creep stage, up to a strain of ~ 0.01. Notably, the frequency of microcrack formation within the T 2 phase temporarily leveled off near the strain corresponding to the minimum creep rate, but increased markedly in the tertiary regime. These results suggest that microcracking within the T 2 phase is one of the dominant creep damage mechanisms in the MoSiBTiC alloy.