Influence of Tool Steel Coating Thickness on the Mechanical and Thermal Properties of Copper Alloy Substrates Fabricated by Laser‐Directed Energy Deposition

Depositing tool steel coatings on copper-alloy molds is an effective strategy to extend mold lifespan, owing to the high strength and ductility of tool steels. However, the coating thickness must be carefully optimized to ensure sufficient surface strength without significantly compromising the thermal dissipation efficiency of the mold. In this study, tool steel coatings with three thickness levels (1.2, 2.8, and 4.5 mm) are fabricated via laser-directed energy deposition to examine their influence on microstructure, microhardness, load-bearing capacity, and thermal conductivity. The results reveal that increasing coating thickness does not necessarily enhance load-bearing capacity: an improvement is observed when the thickness increases from 1.2 to 2.8 mm, whereas a further increase to 4.5 mm leads to a decline. Thermal conductivity exhibits a continuous decrease with increasing thickness. It drops from 159 to 115 J m1 K1 after depositing a 1.2 mm coating, and further decreases to 90 and 75 J m1 K1 for the 2.8 and 4.5 mm coatings, respectively. Overall, a coating thickness of 2.8 mm (five layers) is identified as optimal, achieving the balance between load-bearing capacity and thermal conductivity for mold surface applications.