GRAPHITE FIBER - COPPER MATRIX COMPOSITES
This new metal matrix composite has been trademarked under the name of FiberNide.

Graphite fiber copper - matrix composites are the material of choice for many thermal management applications. Copper has a thermal conductivity of 398 watts/m.°C and a coefficient of thermal expansion of 16.8ppm/°C. The best material to add to the copper to lower and control the expansion is pitch based graphite fiber. These graphite fibers have a high modulus (135 Msi), a thermal conductivity twice that of copper, and a coefficient of thermal expansion of -1.5ppm/°C. For heat sinks where the control of the thermal expansion in the x-y plane is of paramount importance, the milled fiber is the best choice because of the uniform distribution that can be achieved using FiberNide’s propriety process.

CTE OF GRAPHITE FIBER/COPPER COMPOSITES

The coefficient of thermal expansion (CTE) of 0.2mm long milled graphite fiber – copper matrix composites as a function of the volume percent fiber is shown in the upper curve of the attached graph. In the manufacturing method employed, most of the fibers orient themselves in the x-y plane as shown in the attached photomicrograph. For the most requested CTE of 8 ppm/°C, 33 volume percent graphite is required. The x-y thermal conductivity of this composition is approximately 465 W/m.°C while the Z axis conductivity is about the same as copper. In addition to lowering the CTE and improving the thermal conductivity the graphite fiber also improves the stiffness and machineability of the composite.

In some applications the x-y CTE is not important, and a heat pipe with all the fiber oriented in the Z direction is desired. The Z axis CTE of copper - graphite composites made from 1 inch long chopped fiber is shown in the lower curve of the graph. At 33 volume percent graphite, the Z axis conductivity is 530 W/m.°C.