Bonding of high density graphite by brazing with filler metal and sinter bonding with adhesive resin using direct current heating and sufficient pressing was studied. Radiative heating and slight pressing were also tested for comparison. Al, Ag-Cu-Ti, Ni-Cr-B were used for filler metal and phenolic adhesive resin containing graphite powders and hardening material was used for adhesive resin. Joint properties were evaluated by microstructure and bending strength of joint.
Main results obtained are as follows :
(1) At Al, Ag-Cu-Ti, Ni-Cr-B brazing using radiative heating and slight pressing (1.5×10-3 MPa), wettability of filler metal to graphite was very poor and 4 point bending strength of joint was low extremely. At Al, Ag-Cu-Ti, Ni-Cr-B brazing using direct current heating and sufficient pressing (9.8 MPa), above mentioned wettability was improved and 4 point bending strength of joint increased. But, 4 point bending strength of the later brazing joint was lower than bending strength of base graphite (78 MPa). This difference is based on generation of void and cavity.
(2) At sinter bonding with phenolic adhesive resin using radiative heating and slight pressing (1.5×10-3 MPa), voids generated in adhesive resin and 4 point bending strength of joint was low. At sinter bonding with phenolic adhesive resin using direct current heating and sufficient pressing (9.8 MPa), voids disappeared and 4 point bending strength of joint equivalent to bending strength of base graphite (78 MPa) was obtained. This difference is based on generation of void in phenolic adhesive resin.
(3) It was confirmed by gas analysis test that H2O gas generated by condensation-polymerization reaction of phenolic adhesive resin at heating. Removal of H2O gas is important, because H2O gas causes voids in phenolic adhesive resin. Holding at 353–393 K and sufficient pressing at sinter bonding process are effective for removal of H2O gas in phenolic adhesive resin.
