Study on the in situ strengthening and toughening mechanism of H13 tool steel/WC-12Co composite using laser-based directed energy deposition

To overcome the unworkability of hot work molds in conventional manufacturing, laser additive manufacturing (AM) is widely adopted to print molds/dies with complex internal structures. However, in the AM process, some hot work steels easily crack (e.g., H11 and H13 tool steel) or exhibit dissatisfactory wear resistance (e.g., MS1 maraging steel). To tackle this issue, toughened functionally graded metal matrix/ceramic composite materials can be fabricated on existing molds by laser directed energy deposition (L-DED). Contrary to previous studies that clad Co on WC to avoid the decomposition of ceramic, in this work, we innovatively utilized a type of WC12Co powder with a substructure to accelerate its decomposition and improve the toughness of composites. It was found that the unmelted tens-micrometer-magnitude WC-12Co powder and in situ synthesized nano WC coexist in the laser-deposited H13 steel/WC-12Co composites to act as the reinforcement phase. Particularly, all the brittle phases (WC and FexWxC) are wrapped by soft gamma phases, alleviating the coefficient of thermal expansion (CET) mismatch between materials and the residual stress generated by laser AM. Consequently, defect-free deposits with varied WC contents are manufactured by L-DED and exhibit high hardness and superior wear resistance at both room and elevated temperatures due to the second phase and grain refinement strengthening mechanisms. These findings provide a disparate metal matrix composite design route for laser additive manufacturing to improve the toughness of metal matrix/ceramic composite materials and obtain exceptional performance.