3D quantitative microstructural characterization of U-TIG welded Inconel 718 superalloy: Microstructural refinement and mechanical properties enhancement

This paper presents a novel self-induced ultrasonic pulse TIG (U-TIG) process with high efficiency, which improves microstructure and mechanical properties of TIG welds in Inconel 718 (IN718) super-alloy. The characteristics of grain sizes, sub-grain sizes, grain orientations and boundary precipitates in the weld metal were quantitatively analyzed on the three-dimensional (3D) scale. Ultrasonic pulse current not only refines overall dimensions of grains and sub-grains in 3D directions, but also changes grain growth orientations from vertical to oblique. The refinement of grains and sub-grains increases grain boundary length and zigzag degree, while the morphology of the Laves phase transforms from a long-strip shape to a refined pebble-like one. These microstructural evolutions are responsible for the improvement tensile strength (95% of that of the base metal) and ductility (461% of that of the base metal).