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

Abstract

Creep behavior of the Inconel 617 alloy has been investigated through tests carried out in the temperature range of 650 degrees C to 800 degrees 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 degrees C or has an intermediate steady-state regime at 750 degrees C or 800 degrees C. The variation of minimum creep rate (epsilon(min)) with stress (sigma) obeys the power law relationship (epsilon(min) = A sigma(n)), with the stress exponent, n, increasing with temperature to a peak value at similar to 700 degrees 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 degrees C. Investigation of the post-creep microstructures by transmission electron microscope has revealed the formation of gamma ' and M23C6 precipitates, which obstruct dislocation motion during the primary stage. Microstructures of the samples creep-tested at >= 750 degrees C have exhibited relatively smaller amounts of gamma '. 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 gamma ' precipitates.