Monitoring the degree of dilution during directed energy deposition of aluminum bronze and H13 tool steel using optical emission spectroscopy

Controlling heat transfer in casting tools is a key quality aspect. It can be improved by selectively applying volumetric aluminum bronze (CuAl9.5Fe1.2) sections in the core of the tools and subsequently depositing these cores with hard-facing H13 tool steel. Directed energy deposition (DED) can be used for both additive manufacturing of aluminum bronze and hard-facing by depositing the filler material onto a substrate surface or previously manufactured bodies. A sufficient metallurgical bonding of the deposited filler material and the underlying layer must be ensured. Hence, the dilution is a key factor for quality assurance. However, high dilution of the underlying layer and the filler material negatively affects the desired properties and must be monitored. Optical emission spectroscopy of the DED process emissions is investigated by comparing the emission lines of the individual elements comprising the base and the filler materials. Multiple single tracks using aluminum bronze as the filler material are laser-cladded with varying power, onto the two different types of substrates, i.e., mild steel S355 (1.0570) and hot working tool steel H11 (1.2343). Additionally, single tracks of H13 (1.2344) are deposited with varying laser powers onto an additively manufactured core of aluminum bronze. Both resulting in deposition tracks with varying dilution values. Multiple emission lines of Cr, Fe, Cu, Al, and Mn are detected and measured (line intensity). Line intensity ratios using the element emission lines are calculated and correlated with the respective metallographic results of the deposition tracks (dilution and chemical composition). Deposition tracks with a higher dilution (CuAl9.5Fe1.2 onto S355/H11 as well as H13 onto CuAl9.5Fe1.2) showed an increased line intensity ratio of the underlying material to the filler material. Moreover, this technology was transferred in a multilayer industrial application.