Multivariable optimization of WAAM process using Taguchi-based Grey Relational Analysis to improve mechanical properties and corrosion resistance in multilayer stainless-steel structural components

The Wire Arc Additive Manufacturing (WAAM) process is a promising alternative for constructing and repairing large-scale, structurally complex parts with variable shapes and dimensions. However, producing near-net shape WAAM builds with high mechanical properties requires considering the multiple responses issue and controlling several parameters. The present investigation employed the Taguchi method with Grey Relational Analysis (GRA) to optimize all operational WAAM process parameters, considering multiple response performance characteristics. As a novel aspect, the effect of wall tilt angles on the geometric, microstructural, mechanical and electrochemical properties of ASS 308L WAAM structures was studied. First, the geometrical features of a single bead (height, width, and wetting angle) were optimized to ensure multilayered thin-walled WAAM builds with a good height-to-width layer ratio. Then, microhardness and corrosion resistance in multilayered structures of austenitic stainless steel (ASS) grade 308L were improved by applying the same strategy (Taguchi-GRA methods). The ideal objective sequence was determined as a function of the calculated Grey Relational Coefficient (GRC) and Grade (GRG). Both GRC and GRG were analysed using analysis of variance (ANOVA) to determine the statistical significance of the parameters and their contribution to the response variables (geometric, mechanical, and electrochemical properties). Results revealed that the torch inclination had low statistical significance in the performance characteristics of multilayered builds but promoted significant variations in wetting angle (WA). The above affected the formation of humping bead defects at a low orientation angle (60°) due to alterations in the thermal gradient. Also, the dendrite orientation and predominant ferrite morphologies were modified by the WAAM build tilt angle. The lower corrosion rate and higher average microhardness were attributed to the refined and dispersed vermicular and lathy delta ferrite morphologies, which limited the formation of chromium-depleted regions. The formation of columnar dendrites led to the extension of corrosion-susceptible and low-microhardness regions.