Dr Hoque Mozumder, Mark Taylor, Vincenzo Bongiorno, Dr. Yao Lu, Jun Wang, Stewart Williams, Philip B Prangnell, Ed Pickering, Fabio Scenini
The University of Manchester, The University of Manchester, Cranfield University, Cranfield MK43 0AL, United Kingdom, Cranfield University, Cranfield University, University of ManchesterThe University of Manchester
Wire-arc additive manufacturing (WAAM) often leads to elemental microsegregation and non-equilibrium phase formation during rapid solidification, which can compromise the corrosion performances of alloys. This study evaluates the effect of post-printing heat treatment strategies on the microstructure and pitting corrosion behaviour of WAAM processed Custom 465 (C465) martensitic stainless steel. The as-printed WAAM C465 exhibited large columnar prior austenite grains and pronounced microsegregation, which stabilised retained austenite and Laves phases in the inter-dendritic regions. An optimised homogenisation treatment effectively reduced microsegregation and dissolved Laves phases. The pitting corrosion behaviour was comprehensively evaluated using cyclic potentiodynamic polarisation (CPP) and electrochemical noise (ECN) techniques. WAAM C465 exhibited inferior pitting resistance, poor repassivation and higher metastable pitting activity compared to its wrought counterpart. High-resolution surface characterisation following anodic polarisation revealed metastable pit initiation at Cr-depleted inter-dendritic retained austenite and Laves/matrix interfaces in WAAM C465. However, homogenisation (performed prior to standard solution treatment and ageing) significantly enhanced the pitting resistance of WAAM C465 by eliminating preferential sites for metastable pit nucleation and achieving performance comparable to conventionally manufactured wrought counterpart. Overall, this work demostrates the critical role of post-printing heat treatment strategies in addressing WAAM-induced microstructural heterogeneities and mitigating pitting susceptibilities.
