Mechanical properties of steel–copper multi-material samples built by laser powder bed fusion using a graded energy input

Abstract

AbstractLaser powder bed fusion (L-PBF) is a well-established additive manufacturing technology for the fabrication of metallic components. Despite being used in different industries with different materials, the L-PBF process is still today predominantly used for mono-material processing only. While combining different materials during processing is not yet extensively researched, it holds great potential for improving current applications, as well as enabling new ones. In this paper, the material combination of the copper alloy CuCr1Zr and the tool steel 1.2344 is investigated. While copper and its alloys offer high electrical and thermal conductivity coupled with good mechanical properties in terms of strength and ductility, steel offers a significantly higher strength and better wear resistance. Multi-material samples from steel 1.2344 and CuCr1Zr are manufactured by L-PBF using three transition zones, enabling a gradual increase in the applied volume energy density. The application of transition zones successfully eliminated hot cracking and facilitated a narrow steel–CuCr1Zr intermixing zone. The mechanical properties of the manufactured samples are investigated by tensile testing with samples tested in the as-built condition and after subsequent heat treatment. Different heat treatments are applied and evaluated. Furthermore, the fracture surfaces of torn tensile samples and the cross-sectional microstructure of untested samples are visualized by optical and scanning electron microscopy. During tensile testing, a number of samples failed in proximity of the material interface. The fracture surfaces show unmolten powder particles indicating insufficient melting, whereas the cross-sectional images display an accumulation of lack of fusion defects in the CuCr1Zr within a distance of approximately 250 µm from the material interface. Tensile testing results indicate that the observed defects have a significant influence on the elongation to fracture, yet do not show a strong correlation to the yield strength and the ultimate tensile strength. This study emphasizes the current difficulty in manufacturing a defect-free microstructure within the multi-material interface.