Infiltration of Graphite Foams with Cu-1%Cr Alloy for Thermal Management Composites.Lindsey Martin - Purdue Graduate Student
Graphitic foam-copper alloy composites have been produced using a low-pressure infiltration processing technique (LPI). Pure copper does not wet graphite, but an addition of 1 wt %Cr in Cu enables infiltration at pressures less than 1 atm. Two different density foams (Pocofoam and PocoHTC, Poco Graphite, Inc., Decatur, TX) were infiltrated under 1 atm inert gas pressure for different times ranging from 30 to 120 minutes. PocoFoam and PocoFoam HTC both have cell diameters around 200 - 300 microns. PocoFoam is about 80% porous, has a CTE of 1.3 ppm/C and a Thermal Conductivity of 135 W/mK. PocoForm HTC is about 50% porous, has a CTE of 1.9 ppm/C and a thermal conductivity of 245 W/mK making it more desirable for thermal management of electronics. Quantitative stereological measurements showed a time dependent filling of the cells in the more dense foam (HTC), which was most likely due to lower cell connectivity compared to the less dense foam (Pocofoam). Thermal expansion and thermal conductivity measurements are reported and correlated with the composite constituent properties and microstructure.
PocoFoam was able to be 96% infiltrated (by area counting) in 30 minutes of infiltration. PocoFoam HTC, however only achieved 55 to 57% infiltration in the same time. At 60 minutes of infiltration, 81% infiltraion was achieved with PocoFoam HTC in one run. At 120 minutes of infiltration time 90%, 79% and 78% infiltration was achieved with PocoFoam HTC.
CTE (expansion diagrams) showed that the infiltrated samples expand somewhere between the rate of PocoFoam HTC and Cu(Cr1%). On strange occurance in the CTE data was that one of the composite samples when run a second time expanded at a much lower rate than the first time the same sample was tested.
Thermal conductivity data yet needs to be determined, as does appropriate models for this type of composite material property prediction.