Investigations into metallurgical, mechanical, and particulate matter emissions in in situ micropowder alloyed wire arc additive manufacturing process

Wire Arc Additive Manufacturing (WAAM) is an advanced manufacturing technique capable of a high deposition rate and is used for fabricating large-sized and complex components. Of specific interest in the recent past is the in-situ micropowder alloying during filler material deposition to modify the properties of each deposited layer. This study focuses on investigating the metallurgical and mechanical characteristics of the steel produced through powder-added WAAM, using characterization techniques such as optical microscopy, scanning electron microscopy, energy-dispersive spectroscopy and Vickers microhardness testing. Additionally, changes in the size distribution of fine and ultrafine particles (UFP) emitted during WAAM deposition, with and without micropowder addition, were studied using a Scanning-Mobility-Particle-Sizer. Two single-bead multi-layered walls of ER70S6 were deposited in two conditions: as-deposited steel wall and interlayer Titanium micropowder-added steel wall. The results indicate that the microhardness of the Ti micropowder-added steel wall increased by approximately 35% due to the formation of specific microstructures, such as bainitic-ferrite, with retained austenite and mainly due to precipitation strengthening. The emission measurement results suggest that the addition of Ti micropowder during WAAM increases UFP concentration by 20%. The elevated temperature during the deposition process could be a key factor for the rise in particulate matter emissions.