Friction Bonding of Silicon Carbide to Oxygen-Free Copper with an Intermediate Layer of Reactive Metal

Intermediate layers of various metals ranging from reactive metals to noble metals have been applied to friction bonding of SiC (pressureless-sintered silicon carbide) to Cu (oxygen-free copper), and their influences on the bond strength and microstructures of the joint have been systematically investigated by means of TEM observations. When a thin foil of reactive metal, Al, Ti, Zr, or Nb, was applied as the intermediate layer, the bond strength of SiC to Cu was improved considerably. In contrast, when an intermediate layer of Fe, Ni, or Ag was applied, the SiC specimen separated from the Cu specimen immediately after the bonding operation without the application of external load, similar to the case of bonding without an intermediate layer. During friction bonding with an intermediate layer of reactive metal, the intermediate layer was mechanically mixed with Cu lo form a very complicated microstructure extending over a region as wide as a few 100 μm TEM observations have revealed that very thin reaction layers between the SiC and reactive metals were formed. When the Ti intermediate layer was applied, a TiC layer 10-30 nm thick was formed over almost the entire area along the interface, and between this layer and the SiC matrix a very thin layer of a Cu solid solution was detected. On the other side of the TiC layer, a Ti 5 Si 3 layer ∼100 nm thick was partially observed. When the Nb or Zr intermediate layer was applied, a very thin interfacial layer, in which Nb or Zr was significantly concentrated, was observed in addition to the reaction layers of Nb 5 Si 3 , NbC, and ZrC. These interfacial layers can he characterized by their much smaller thickness and finer grain size than those observed in diffusion-bonded and brazed joints. Apart from the layers mentioned above, amorphous silicon oxide layers were occasionally observed, suggesting that the reactive metal enhanced the removal of the oxide film on the SiC surface.