Microstructural evolution, crystallographic texture, grain morphology, and mechanical integrity of wire arc additively manufactured Inconel 625 alloy

Abstract

The material in wire arc additive manufacturing (WAAM) undergoes complex material flow and multiple thermal heating and cooling cycles, forming highly heterogeneous microstructures in terms of size, crystallographic orientations, and mechanical properties. The inhomogeneity also depends on the dislocation density and phases, which are influenced by the thermal history of the process. In this study, the Cold Metal Transfer (CMT) process was used to deposit a 60-layer build of Inconel 625 alloy. Detailed variations in the microstructural size, orientations, and phases along the building direction were studied using optical microscopy, electron backscatter diffraction (EBSD), and X-ray diffraction (XRD). Microstructural observations reveal dendrites, equiaxed crystals, cellular, and columnar structures with primary and secondary dendrites. Dynamic recrystallization (DRX) followed by abnormal grain growth was found in the build. The average grain size varies with deposited height, with a grain size of around 13 ± 1 μm near the substrate, 45 ± 1 μm in the middle region, and 18 ± 1 μm at the top. The top region exhibited a strong intensity of recrystallized Cube, Cube-ND, and Cube-RD textures, with weaker intensities of copper and brass textures. The middle and bottom regions show strong intensities of Goss, copper, F, S, and E textures, respectively. The highest dislocation density of 5.122 × 10⁻⁴ nm⁻² was found in the top region, while the lowest (4.14 × 10⁻⁴ nm⁻²) was observed in the bottom region. The ultimate tensile strength of the build ranged from 603 ± 05 MPa to 699 ± 10 MPa, while the yield strength varied from 313 ± 07 MPa to 365 ± 08 MPa along different orientations. Vickers hardness results showed a slight variation, from 240 ± 5 to 260 ± 2 HV, from bottom to the top of the deposited build. The findings from this study provide valuable insights into the microstructural evolution mechanism and mechanical behavior of WAAM-fabricated Inconel 625, which can guide other researchers in optimizing process parameters, enhancing material properties, and understanding the effects of thermal history on additive manufacturing of high-performance alloys.