Microstructure and Mechanical properties of a Reversed Engineered Inconel 625 Produced by Direct Energy Deposition

Abstract

The purpose of this study is to investigate the micro-structural and mechanical properties of reverse engineered Inconel 625 manufactured by direct energy deposition (DED). A costume made 4kW robotized DED machine was used for the manufacturing of specimens. Mechanical and micro-structural properties of the specimens are studied in as-build condition and after heat treatment for 60-, 120- and 300 minutes at 1175 C. This study provide a comparison of micro-structural and mechanical properties of as-build and heat treated specimens. Mechanical properties of the specimen are studied by performing Vickers hardness and tensile test. Analysis of the micro-structural properties is performed using scanning electron microscope (SEM), transmission electron microscope (TEM), X-ray spectroscopy (EDS), electron backscatter difraction (EBSD) and X-ray diffraction (XRD). It was found that the super alloy is very durable and shows average hardness (HV5) of 257.7HV in as-build condition which decreased to 215HV on heat treatment (30 min) due to reduction of residual stress and relaxation of dislocations. Difference in mechanical properties is observed within the specimen e.g hardness differs from top to bottom. Change in tensile strength is observed in as-build and heat treated specimens. The tensile test resulted in a brittle fracture in both as-build and heat treated specimens. As-build specimens showed cellular and columnar structures, while equiaxed structure and coarse grains are observed in heat treated specimens. Welding defects such as cracks and pores are also observed in both as-build and heat treated specimens. EBDS shows misorientation angle of most of the grains is between 1◦ to 3.5◦ in as-build specimen and 0◦ to 60◦ on the 300 minute heat treated specimen. It is observed that recovery of grains happened in the heat treated specimens. However, there was no evidence of recrystallization in any of heat treated specimen. No precipitates or any change in chemical composition was observed in heat treatment (1175◦C) specimens. The hardness, yield strength and residual stress of additive manufactured (AM) Inconel 625 super alloy decrease on heat treatment while the alloy become more ductile.