Heat flux experiments on first wall mock-ups coated by plasma sprayed B4C

The plasma compatibility of the first wall of fusion devices can be achieved either by using protective tiles of massive material like fibre reinforced carbon or by direct coating of the metallic wall. For ITER, the plasma spray technique provides the opportunity to coat large areas of the first wall with coating thicknesses of the order of 1 mm and may allow in-situ repair of the coating. Plasma sprayed boron carbide (B4C) is regarded as a promising candidate material because of its low atomic number and high melting point. In the present work, actively cooled stainless steel AISI316L bodies were coated with a copper interlayer and a 1.2 mm top layer of B4C. The homogeneously coated surface was 210 mm × 65 mm. The stainless steel bodies had two parallel channels for water cooling of the mock-ups. Thermomechanical testing was performed in the JEBIS-facility (JAERI Electron Beam Irradiation System). Surface heat loads of 0.5-1 MW/m2 caused local delamination and cracking of the coating.