Microstructure and mechanical properties of super-invar alloy fabricated by wire-arc additive manufacturing

Here, wire-arc additive manufacturing (WAAM) is employed to manufacture a super-invar alloy thin-wall rectangular component. The microstructure is characterized by cellular sub-grains with different morphologies inside the epitaxially grown columnar crystals. Based on the finite element simulation results, the value of the G (the temperature gradient)/R (the solidification rate) during the deposition process is calculated as 1.59 ×10⁸ K·s·m⁻², which is associated with the columnar cellular microstructure. The transfer mode of the droplet during the WAAM is liquid bridge transition. The mechanical properties of specimens are anisotropic, and the longitudinal samples are better than transverse samples; the UTS is 398.8 MPa, the YS is 291.4 MPa, and the elongation is 40.8%. The coefficient of thermal expansion (CTE) is measured to be 0.265 ×10⁻⁶ K⁻¹ in the range of 20 °C to 100 °C. The findings provide a reference for the fast fabrication of super-invar alloy components through WAAM, which promotes the applications of super-invar alloy in aerospace.