Selective laser melting of metal structures onto graphite substrates via a low melting point interlayer alloy

We demonstrate a process to selective laser melt a metal alloy directly onto graphite. The heat transfer applications of metal features printed onto annealed pyrolytic graphite are compelling, as pyrolytic graphite has the second highest in-plane thermal conductivity (>1500 W/m-K at room temperature) of any bulk material. While the bonding of metal alloys commonly used in selective laser melting (SLM) with graphite is relatively weak, the proper interlayer material drastically improves the wetting and bonding. The challenge is the alloys that typically bond to graphite require extended bonding times at elevated temperatures (minutes to hours), while the SLM process delivers only brief exposures to high temperatures (∼100 µs). In this paper, we employ a Sn3Ag4Ti alloy that rapidly forms a nanometer-thin layer of TiC, as verified by transmission electron microscopy. The influence of graphite thermal properties on interfacial bond strength is shown by mechanical testing and simulations of selective laser melting.