Development of brazing technologies for bonding of graphite and CuCrZr joints applying for the first wall of the EAST device

Bonding between plasma-facing materials (PFMs) and heat sinks is an important factor for the performance of plasma-facing components (PFCs) in the tokamak device; in some specific applications, graphite is adopted as the plasma-facing material and CuCrZr as the heatsink. Bonding of graphite and CuCrZr is a critical and difficult process due to the poor wettability of graphite and wide gap of material properties between graphite and CuCrZr, to which should be paid more attention. Herein, brazing processes were developed to achieve the bonding of CuCrZr and graphite, and a layer of oxygen-free copper (OFC) was placed between graphite tiles and CuCrZr heat sinks as a stress-buffer layer. Three types of brazing fillers including Ti powder with AgCu foil, AgCuTi paste and AgCuTi foil were used to achieve the bonding of CuCrZr and graphite. Samples were tested by scanning electron microscopy (SEM), energy dispersive spectrometry (EDS) and shear strength experiment; the results showed that these three types of fillers can achieve the bonding of CuCrZr and graphite. In addition, one-step brazing and multi-step brazing were both developed to achieve the bonding of graphite/OFC/CuCrZr, and the mock-ups were manufactured and endured cyclic high heat loads in the high heat flux (HHF) tests. In conclusion, the simplified one step brazing process including types of fillers, brazing temperature and brazing sequence was determined, which provides a promising premise method for the heat transfer structure design of PFCs.