Effect of different strain rates on mechanical behavior and structure of Inconel 718 produced by powder bed fusion

The paper aims to examine the effect of different strain rates on a mechanical behavior and structure of additively manufactured Inconel 718. The material was prepared by the powder bed fusion method, which is commonly employed for high-performance components subjected to both high static and dynamic loading. To analyze the material’s behavior at various strain rates, a conventional hydraulic testing machine and a split hopkinson pressure bar apparatus were utilized. Additionally, the effect of these conditions on mechanical properties and microstructure was investigated. Results of compressive tests revealed a positive strain rate sensitivity of the material. Furthermore, the microhardness exhibited an increase by 33.9% in the horizontal direction after deformation caused by 2·10^–2 strain rate and 35.8% in the vertical direction, respectively. Additionally, the average grain size decreased by 43.3%, and the high-angle grain boundaries decreased by 5.4% in the horizontal direction after the excessive plastic deformation at the strain rate of 1.8·10³ s^-1. Scanning electron microscopy images showed that the as-built structure predominantly consisted of Laves phases in a long strip shape, while the structure after dynamic testing featured a granular shape. Transmission electron microscopy analysis of a sample tested at strain rate of 0.002 s^-1 revealed finely developed grains within the structure, many of which contained a dislocation substructure. This study’s novelty and robustness lie in its significant contribution to practical industrial energy applications, in which parts are exposed to dynamic load such as gas turbines.