Effect of heat transfer in substrate on microstructure and tensile behavior of deposits built by directed energy deposition

Abstract

This study was aimed at analyzing the properties of the deposited material and interface on a substrate containing an inner lattice structure, layered using directed energy deposition (DED). The substrate with the lattice structure was fabricated using powder bed fusion (PBF) and then layered using a heterogeneous material through DED. Subsequently, the temperature changes of the substrate were monitored during layering, and its correlation with the properties of the deposited material were investigated. The results revealed that the lattice substrate exhibited a high heating and cooling rate during layering. Moreover, the temperature near the deposited region of the substrate was higher than that of the solid sample. This heat transfer property of the substrate resulted in a thick fusion or transition zone at the substrate-deposits interface. Owing to the rapid cooling rate of the lattice substrate, the microstructure of the deposited region was predominantly cellular grain, and the formation of the Laves phase was suppressed. In the tensile test, the lattice samples showed fractures within the substrate region. This was attributed to the formation of a transition zone in the interface of the lattice sample, where the compositions of the two heterogeneous materials gradually fused. In contrast, the interface of the solid sample had a narrow transition zone, leading to non-convergent fracture locations and tensile properties due to inadequate fusion at the interface. Additionally, the dominant Laves phase in the deposited region of the solid sample was identified as a factor contributing to the delamination near the interface.