Tensile, fatigue and creep response characterisation of direct energy deposited Inconel 718: anisotropy and effects of heat treatment

This study reports the outcomes of a comprehensive mechanical testing programme for direct energy deposited Inconel 718 in as-built and heat-treated conditions. After investigating the microstructure and hardness of the alloy in both conditions, the study focuses on investigating the tensile, strain-controlled low cycle, stress-controlled high cycle fatigue, as well as the creep response of the alloy for samples loaded parallel and perpendicular to the build direction. The tensile tests were conducted at room temperature and at 600, 650, and 700°C; creep tests were conducted at 650°C, and fatigue tests were performed at room temperature. It was found that samples loaded perpendicular to the build direction show superior tensile and creep strength for both as-built and heat-treated states. Furthermore, heat treatment consistently enhanced the tensile and creep strength of the alloy. Meanwhile, a lower level of anisotropy and difference between as-built and heat-treated responses was observed from fatigue response of the alloy.