In this PDF by W.Y. Maeng from the Korean Atomic Energy Research Institute, the author discusses a novel heatsink fabricated from graphite brazed to a copper baseplate for a proton accelerator. The one step brazing process for the joining of Cu-graphite plate uses TiCuSil alloy. There is some interesting cooling technology being discussed here, but keep in mind that while Graphite has a relatively good thermal conductivity it is generally only in one plane). This research note goes on to test IG-430 graphite impregnated with Cu and Ag alloys.
"The graphite used for front facing material is
IG-430 of Toyo Tanso. The copper plate for the
cooling jacket material is made with OHFC
(Oxygen Free High Conductivity Copper, ASTM
B170 Grade 1). The filler material for the brazing
is TiCuSil alloy (4.5%Ti-27.7%Cu-68.8%Ag,
FULL STORY @ ICENES2007 (http://www.icenes2007.org/icenes_proceedings/manuscripts.pdf/Session%203B/DEVELOPMENT%20OF.pdf)