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

Abstract

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.