Laser Metal Additive Manufacturing on Graphite
Metal powders are typically directly fused to a metal substrate of similar composition in metal powder-bed fusion additive manufacturing. This work presents a process for printing a metal alloy directly on graphite, rather than a metal platform. This technology has attractive applications to heat transfer, as this process can be used to directly print heat sinks or heat exchangers on pyrolytic graphite. The heat transfer applications of metal-pyrolytic graphite are enormous, as pyrolytic graphite has the second highest thermal conductivity (>1700 W/m-K at room temperature) of any bulk material, with only expensive diamond exceeding it. Bonding of common metal alloys used in additive manufacturing and graphite are relatively weak and possess high contact angles. However, by using the proper interlayer material, wettability and reactivity of the graphite substrate with metal powder can increase drastically. The alloys that can typically bond to graphite require extended times at elevated temperatures (minutes to hours), while this study demonstrates rapid bonding (~100 µs).