Research on brazing technology of graphite/OFC/CuCrZr joints with CuSnTi fillers applying for carbon-based plasma-facing components

Abstract

Plasma-facing components (PFCs), which consist of plasma-facing materials, heat sink materials, and support materials, are designed to withstand plasma shock directly and heat load during tokamak device operation; therefore, the bonding of graphite (plasma-facing material) with CuCrZr (heat sink material) is a critical technology for manufacture of PFCs. In this paper, oxygen-free copper (OFC) and CuSnTi foil were employed as the stress-relieving layer and brazing filler respectively, and graphite/CuSnTi/OFC/CuSnTi/CuCrZr brazing joints were fabricated under various brazing process parameters. The distribution of reaction products and joint-formatting mechanism were analyzed by scanning electron microscope (SEM), energy disperse spectroscopy (EDS) and X-ray diffractometer (XRD), and optimal brazing process parameters were determined by microstructure and mechanical property test results. The brazing joints exhibited a shear strength of 24 MPa when brazed at 1213 K with holding time of 15 min, and the mock-up fabricated using the CuSnTi filler endured 7 MW m⁻² for 1000 thermal fatigue cycles of 15 s heating and 15 s cooling in high heat flux (HHF) tests, which verified the feasibility of its application under high thermal load conditions. The OFC layer within the joint can effectively relieve the thermal stress under high thermal load conditions. Moreover, the bonding of graphite, OFC and CuCrZr was realized in a one-step brazing process, thereby simplifying the manufacturing process while ensuring both mechanical properties and heat removal ability. This advanced brazing technology provides technological support for the fabrication of carbon-based PFCs in experimental tokamak devices.