Microstructure and mechanical properties of Co-free maraging steel fabricated by double-wire CMT + P arc-directed energy deposition

A Co-free maraging steel component, demonstrating excellent forming quality and freedom from internal defects, was successfully fabricated using the double-wire CMT + P arc-directed energy deposition (DED-Arc) process at a deposition rate of 6.4 kg/h. The microstructural evolution and mechanical properties of the deposited component were examined. Results revealed the component possessed a multi-layer structure along the building direction. Horizontally, it exhibited an alternating structural pattern comprising overlap areas (OA) and central fusion zones (CFZ). The overall microstructure consists of martensite, austenite, and Ni₃Ti precipitates. Austenite content increased and grain size decreased towards the bottom, attributed to varying heat dissipation conditions and inherent thermal cycles during DED-Arc. Compared to the OA, the CFZ exhibited a finer grain size and a higher proportion of high-angle grain boundaries (HAGBs); however, no significant difference was observed in the distribution of Ni₃Ti precipitates between the two regions. Tensile strengths were measured at 1163 ± 32 MPa (X), 1183 ± 33 MPa (Y), and 1135 ± 11 MPa (Z). Corresponding impact toughness values were 34.5 ± 3.1 J/cm² (X), 34.3 ± 1.9 J/cm² (Y), and 37.8 ± 4.3 J/cm² (Z). Ductile fracture predominated in both tension and impact tests. Microhardness in the top region was relatively low due to heat accumulation and thermal history variations. Furthermore, microstructural differences between the OA and CFZ led to higher microhardness in the CFZ. These findings demonstrate the successful application of the double-wire CMT + P DED-Arc process for maraging steel, providing an important reference for the future development of efficient, high-performance DED-Arc processes.