Influence of deep cryogenic treatment on microstructure and mechanical behavior of Inconel 686 alloy produced by DP-GMAW wire arc additive manufacturing

In this investigation, Inconel 686 components were produced utilizing wire arc additive manufacturing (WAAM) with a double-pulsed gas metal arc welding (DP-GMAW) technique. The study focused on analyzing the microstructural evolution and mechanical performance of the fabricated parts, as well as evaluating the influence of deep cryogenic treatment (DCT) on these characteristics. Microstructural examination was carried out across different layer of the specimen, specifically, the upper, middle, and lower sections. Observations from optical microscopy and scanning electron microscopy (SEM) revealed that the DCT-processed sample featured a refined equiaxed grain structure at the top, short columnar and cellular dendrites in the middle, and fine cellular dendrites at the base. To assess grain characteristics, X-ray diffraction (XRD) analysis was employed, indicating a reduced average crystallite size of 16.28 nm and an elevated dislocation density of 37.73×10 -4 nm -2 in the DCT-treated specimen compared to the untreated build. Elemental distribution and segregation were assessed using energy-dispersive X-ray spectroscopy (EDS), both through point analysis and elemental mapping. The findings showed minor molybdenum (Mo) segregation in the as-built material, which was effectively suppressed in the DCT-treated sample due to grain refinement. Mechanical testing, including Vickers hardness and tensile evaluations, was used to measure properties such as hardness, tensile strength, yield strength, and ductility. The DCT-treated component demonstrated improvements of 7.85% in hardness, 7.2% in tensile strength, and 2.3% in ductility relative to the as-built counterpart. Moreover, DCT treatment was found to mitigate anisotropy and structural heterogeneity present in WAAM-fabricated Inconel 686.