Influence of the manufacturing strategy on the microstructure and mechanical properties of Invar 36 alloy parts manufactured by CMT-WAAM

Abstract

The influence of the manufacturing strategy of Invar 36 alloy parts manufactured by Directed Energy Deposition by Arc (DED-Arc) also known as wire and arc additive manufacturing (WAAM) using cold metal transfer (CMT) technology has been investigated. This study focuses on the influence of applying different deposition strategies on the resulting microstructure and mechanical properties. As manufacturing costs and time are critical issues which determine the business case in WAAM applications, it is important to use the smallest possible amount of feedstock material. Therefore, different manufacturing strategies are used to obtain the variable wall thicknesses required for each part preform using WAAM as a manufacturing route. Differences in manufacturing temperature and thermal history due to different deposition strategies have been recorded. Deep microstructural analysis in as-built condition revealed that granular alignment and the crystallographic texture obtained differ between deposition strategies studied. This is the reason why there are differences in the mechanical properties, such as yield strength, ultimate tensile strength, elongation, and hardness, of the different strategies analyzed. The results revealed that the higher strength is obtained in three overlapped weld beads for the walls (514 and 581 MPa in building direction and perpendicular direction, respectively), compared to single weld bead wall (481 and 489 MPa), circular single weld bead wall (460 and 484 MPa), and meandering weld bead wall (467 and 439 MPa). The opposite is true for elongation, which is a typical correlation between strength and ductility in Fe-based alloys, having the highest elongation in the meandering weld bead wall (26 and 30%) and circular single weld bead (30 and 27%) compared to single weld bead wall (27 and 23%) and three overlapped weld bead wall (23 and 20%). It can therefore be concluded that an Invar 36 alloy part manufactured by CMT-WAAM with different strategies will have different mechanical properties, having a difference in ultimate tensile strength of 54 MPa and 142 MPa, and in elongation of 7% and 10% in building direction and perpendicular direction, respectively, between the most and the least resistant zone.