Laser-assisted substrate heating for crack mitigation in laser metal deposition

Abstract Laser Metal Deposition (LMD) is widely applied for repairing components and reinforcing molds and tools due to its ability to locally deposit metal onto target materials. However, when cemented carbides are deposited onto steel substrates, the mismatch in material properties and rapid thermal cycling often lead to crack formation in the overlay. To address this issue, this study investigates the effect of localized laser heating of the substrate during the LMD process on crack suppression. A multi-beam laser powder deposition system equipped with dual laser beams was employed, allowing simultaneous cladding and substrate heating. WC–12 wt% Co powder was deposited onto S50C steel while varying the output power and irradiation position of the substrate heating laser. Crack formation was evaluated using digital microscopy, and microstructural changes were analyzed through Vickers hardness testing and SEM observation. Additionally, numerical simulations based on the two-dimensional heat conduction equation were performed to analyze temperature histories under different heating conditions. The results revealed that crack formation was most effectively suppressed when the substrate heating laser was positioned 0.5 mm from the cladding path and operated at output power of 30 W or higher. Under these conditions, dendritic structures appeared in the overlay, suggesting a change in solidification behavior. Thermal simulations showed that substrate heating led to a more gradual temperature decrease after the peak, particularly at 50 W and 0.5 mm offset, indicating a reduced cooling rate. These findings demonstrate that localized laser heating of the substrate during cladding effectively reduces thermal strain by lowering the cooling rate, thereby contributing to crack suppression.