Friction bonding of silicon carbide to oxygen-free copper with an intermediate layer of reactive metal (reprinted from Journal of the Japan Instituteof Metals, vol 65, pg 895-904, 1999)

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 b ond strength and microstructures of the joint have been systematically inve stigated by means of TEM observations. When a thin foil of reactive metal, Al, Ti, Zr, or Nh, 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 cast: of bonding without an intermediate lay er. During friction bonding with an intermediate layer of reactive metal, t he intermediate layer was mechanically mixed with Cu to form a very complic ated microstructure extending over a region as wide as a few 100 mum. TEM o bservations have revealed that very thin reaction layers between the SIC an d reactive metals were formed. When die 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 Ti5 Si3 layer similar to 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 reac tion layers of Nb5Si3, NbC, and ZrC. These interfacial layers can be charac terized by their much smaller thickness and finer grain size than those obs erved in diffusion-bonded and brazed joints. Apart from the layers mentione d above, amorphous silicon oxide layers were occasionally observed, suggest ing that the reactive metal enhanced the removal of the oxide film on the S IC surface.