Heat input and shielding environment effect on CMT-WAAM of IN718

Abstract

Shielding gas plays a vital role in customising the weld bead characteristics. This study explores the effect of shielding gases at different heat inputs of welding considering wire arc additive manufacturing (WAAM) of Inconel 718 on its bead geometry characteristics, microstructure evolution and mechanical properties. Bead-on-plate experiments were fabricated using the cold metal transfer (CMT) technique of gas metal arc welding (GMAW) using Taguchi’s L9 orthogonal array. ANOVA and S/N ratio approaches were used to analyse factor effects, their contribution and optimum level. For heat input determination, the dynamic characteristics of the welding power source are recorded and processed. Higher bead geometry characteristics and wider heat affected zone (HAZ) area were observed with increased heat input. The increase in CO₂ concentration in the Ar + CO₂ mixture changed the weld texture from silver metallic (with pure Ar) to grey with 2.5% CO₂ and light yellow with 20% CO₂. Higher bead width, reinforcement, penetration and dilution were observed when 20% CO₂ was mixed with Ar. With 2.5% CO₂, beads were continuous and smoother with all heat inputs. While with 100% Ar shielding environment, higher hardness is obtained compared to welds prepared with 2.5% CO₂ and 20% CO₂ mixed with Ar. The presence of a higher concentration of Nb-riched precipitates, observed from SEM-EDS analysis, resulted in higher strength. The findings of this experimental investigation will empower the WAAM researchers and practitioners to enhance the weld quality and optimize its geometrical characteristics.