Thermo-Mechanical Fatigue Investigation of Inconel 718 Based on Miniature Specimen Testing

Abstract

Thermo-mechanical fatigue (TMF) is a critical degradation mechanism affecting gas turbine components. Testing under realistic loading conditions, such as TMF, is essential for these highly stressed, safety-relevant components. Most existing test setups utilize standard specimens that rarely represent the geometrical sizes of the actual engine components. Although there is interest in using smaller sized specimens to reduce material usage and allow for testing that closely resembles real-life conditions, only a few setups currently facilitate cyclic mechanical testing of small-scale specimens. This paper addresses the need for test rigs designed for TMF testing miniature specimens under realistic thermal gradients and mechanical loads. It focuses on developing a low-cycle fatigue miniature specimen test system validated with nickel-based superalloy Inconel 718. The study compares two specimen sizes to evaluate the impact of size, strain rates, and heating and cooling rates on fatigue life, applying cyclic temperature loading in both in-phase and out-of-phase loading conditions.