Investigation of Single and Double Pulse Techniques on Microstructure and Mechanical Anisotropy of Inconel 686 Component Fabricated by Wire Arc Directed Energy Deposition

Abstract

In this study, thin-wall components of Inconel 686 were fabricated using gas metal arc welding-based wire arc directed energy deposition (WA-DED) with both single pulse (SP) and double pulse (DP) techniques. The microstructure and mechanical properties of the fabricated components were analyzed across various regions, including the lower, middle, and upper sections along the vertical direction, in the horizontal and inclined directions. Microstructural studies revealed variations in the microstructure across different regions of the as-built components, influenced by the degree of constitutional undercooling and layer-by-layer deposition process. SP-GMAW showed columnar dendrites in the lower and middle regions, transitioning to equiaxed dendrites in the upper region. In contrast, DP-GMAW exhibited cellular dendrites in the lower region, short columnar dendrites in the middle, and fine equiaxed dendrites in the upper region. DP-GMAW reduced the crystallite size to 20.05 nm and increased the dislocation density to 24.8 × 10^‒4 nm^‒2 compared to SP-GMAW. The controlled thermal cycles in DP-GMAW promote rapid solidification and inhibit large grain growth. This technique also minimized elemental segregation by creating a dynamic stirring effect through alternating pulse intensities, enhancing mixing and refining the microstructure. As a result, DP-GMAW significantly improved the mechanical properties of WA-DED-fabricated samples, leading to a 4.78% increase in hardness and a 5.84% increase in tensile strength. Moreover, it achieved a 9.3% reduction in anisotropy and heterogeneity, attributable to improved heat control and cooling rates.

Graphical Abstract