Copper-Beryllium precipitation hardening alloys are widely used to manufacture molds in plastic injection moulding due to the excellent thermal properties combined with good mechanical strength and corrosion resistance. However, the lower hardness and wear resistance compared to tool steel, as well as the higher cost, limited their wider use. A tool steel cladding on copper alloy substrate represents a suitable solution to overcome these limitations. Among the candidate cladding techniques, direct laser metal deposition (DLMD) seems to be a proper solution due to its flexibility, the possibility to fabricate thick cladding (1mm) and even 3D structures. However, a direct DLMD of tool steel showed critical issues such as cracks and lack-of-fusion. Substrate preheating can inhibit above defects but it will meanwhile damage the substrate strength due to overaging. Thus, appropriate deposition strategies were considered in order to avoid the use of substrate preheating.
In this work, AISI H13 hot-work tool steel was cladded by DLMD on Moldmax-HH Cu-Be alloy substrate. Different deposition strategies involving i) an intermediate buffer layer (austenitic stainless steel and Ni-superalloy) and ii) functionally graded architecture, were considered to try to inhibit cracking and lack-of-fusion.
The microstructure of samples was analyzed by optical and scanning electron microscopy. Energy Disperse Spectroscopy was used to evaluate interface diffusion of Cu, Fe, and alloying elements. Microhardness profiles were determined to evaluate the influence of buffer layer and functionally graded structure on surface (tool steel) and substrate (CuBe) hardness. The mechanical and thermal properties including load bearing capability (LBC) and thermal conductivity (TC) were also investigated. The results showed that the Ni-superalloy buffer led to crack-free cladding. FGM suppressed cracking but did not totally eliminate it. LBC and TC can be tuned changing the ration between cladding/substrate thickness.