Creep–Fatigue Interaction of Inconel 718 Manufactured by Electron Beam Melting

Abstract

Electron beam melting of Ni‐base superalloy Inconel 718 allows producing a columnar‐grained microstructure with a pronounced texture, which offers exceptional resistance against high‐temperature loading with severe creep–fatigue interaction arising in components of aircraft jet engines. This study considers the deformation, damage, and lifetime behavior of electron‐beam‐melted Inconel 718 under in‐phase thermomechanical fatigue loading with varying amounts of creep–fatigue interaction. Strain‐controlled thermomechanical fatigue tests with equal‐ramp cycles, slow–fast cycles, and dwell time cycles are conducted in the temperature range from 300 to 650 °C. Results show that both dwell time and slow–fast cycles promote intergranular cracking, gradual tensile stress relaxation, as well as precipitate dissolution and coarsening giving rise to cyclic softening. The interplay of these mechanisms leads to increased lifetimes in both dwell time and slow–fast tests compared to equal ramp tests at higher strain amplitudes. Conversely, at lower mechanical strain amplitudes, the opposite is observed. A comparison with results of conventional Inconel 718 indicates that the electron‐beam‐melted material exhibits superior resistance against strain‐controlled loading at elevated temperatures such as thermomechanical fatigue.