Creep Deformation Behavior of Inconel 617 Alloy in the Temperature Range of 650 °C to 800 °C

Creep behavior of the Inconel 617 alloy has been investigated through tests carried out in the temperature range of 650 °C to 800 °C under 95 to 350 MPa. Creep curves obtained from tests on the alloy exhibit a non-classical nature, with the primary creep rate decreasing to a minimum value, followed by a typical increase, which is either continuous at temperatures ≤ 700 °C or has an intermediate steady-state regime at 750 °C or 800 °C. The variation of minimum creep rate (έmin) with stress (σ) obeys the power law relationship (έmin = Aσn), with the stress exponent, n, increasing with temperature to a peak value at ~ 700 °C. The value of n > 5 has been rationalized by considering the existence of threshold stress, which like n has been found to decrease sharply with temperature beyond 700 °C. Investigation of the post-creep microstructures by transmission electron microscope has revealed the formation of γ′ and M23C6 precipitates, which obstruct dislocation motion during the primary stage. Microstructures of the samples creep-tested at ≥ 750 °C have exhibited relatively smaller amounts of γ′. The existence of threshold stress and the steady-state regime in the tertiary creep stage has been ascribed to obstruction of dislocation motion by M23C6 and γ′ precipitates.