In-situ dry ice impact-assisted wire-arc directed energy deposition of H13 steel: synergistic improvement of surface quality, mechanical properties and microstructure

• A novel in-situ dry ice impact cooling (DIIC) strategy is proposed for WA-DED of H13 steel, enabling continuous additive manufacturing. • DIIC reduces surface waviness by 14.1%, significantly improving forming accuracy and surface quality. • Rapid cooling induces multiscale microstructural optimization, including martensite refinement, increased dislocation density, and a more uniform dispersion of nanocarbides. • The strengthening mechanisms originate from the synergistic effects of dislocation strengthening, precipitation strengthening, and grain boundary strengthening. Wire-Arc Directed Energy Deposition (WA-DED) is prone to severe heat accumulation due to its layer-by-layer deposition nature, which adversely affects macrostructure, microstructure, and mechanical properties, thereby limiting industrial application. To address this issue, this study proposes an in situ dry ice impact-assisted WA-DED process, in which compressed air propels dry ice particles to achieve rapid cooling of each deposited layer. A systematic comparison was conducted between H13 steel specimens fabricated under Air Cooling (AC) and Dry Ice Impact Cooling (DIIC) conditions. The results show that DIIC significantly enhances heat dissipation and reduces surface waviness, thereby improving forming quality. At the microstructural level, DIIC promotes grain refinement, increases dislocation density, and results in a more uniform distribution of precipitates. Consequently, hardness, yield strength, and tensile strength increase by 10.7%, 14.9%, and 14.4%, respectively. Meanwhile, elongation and impact toughness decrease by 0.5% and 12.4% due to increased brittle phases. Overall, the strengthening effect outweighs the loss in ductility. Combined with its efficiency advantage, DIIC shows strong potential for applications requiring high wear resistance and load-bearing capacity, providing a basis for improving WA-DED performance.