Joining of Ti coated graphite to heat sink material

Joining of graphite to heat sink material (CuCrZr) is an interesting area in fusion community. At present in SST-1 like tokamak, graphite joining with CuCrZr (heat sink) is considered for plasma facing component. However, the graphite tiles are attached to heat sink material by physical and mechanical bolting mechanism. The direct metallurgical joining of carbon with CuCrZr material is a problematic as having the large mismatch of coefficient of thermal expansion (CTE) between the carbon and copper, where the CTE ratio between carbon and copper is reported to be 1:16. To metallize and to improve the wettability of the carbon surface, typically active element coating is done in prior such as Titanium (Ti) coating or chromium coating is done on the carbon surface. In this paper, we chose Ti coating, which is achieved by sputtering technique using RF magnetron sputtering device. Once the carbon surface is being metallized by Ti coating then the joining of copper is employed by OFHC copper casting route at 1125°C for 2 h under Ar+4%H₂ atmosphere. Finally, the vacuum brazing is carried out in Gleeble 3800 system for the joining of copper cast Ti coated graphite with heat sink material at 980°C using TiCuNi₇₀ brazing filler. Characterizations such as NDT-UT, metallography study and micro hardness measurement of the sample have been carried out. The experimental details and results of the characterization are presented in the paper. (author)