Effects of Ultrasonic Vibration on Microstructure, Mechanical Properties, and Fracture Mode of Inconel 625 Parts Fabricated by Cold Metal Transfer Arc Additive Manufacturing

Ultrasonic vibration was applied in cold metal transfer (CMT) arc additive manufacturing of Inconel 625 parts with the purpose to study the effects of ultrasonic vibration on weld formation, microstructure, and mechanical properties. Forming geometry can be affected by ultrasonic vibration during CMT arc additive manufacturing, especially reducing weld penetration and the penetration rate, by measuring weld width, weld penetration, contact angle, and penetration rate. Performed by optical and scanning electron microscopy, the dendrite grains were refined and the directional growth of coarse columnar grains was also suppressed in the CMT welds with ultrasonic vibration. Energy dispersive spectrometry and x-ray energy-dispersive spectrometry were also used to evaluate the composition of the phases, which show the second phases of laves enriched in Mo and Nb were segregated at the grain boundary of gamma-Ni dendrites and columnar grains. Comparing traditional CMT processed samples, tensile strengths which reached 677.1 +/- 4.6 MPa were improved in the transverse direction with the ultrasonic vibration. All of the sample fracture occurred in a transcrystalline ductile mode, but the dimples were denser and more uniform on fracture surface of tensile samples with ultrasonic vibration.