Properties of plasma sprayed boron carbide protective coatings for the first wall in fusion experiments

In this study stainless steel substrates were coated by vacuum plasma spraying with a two-layer system consisting of a bond coat of 40 μm nickel–chromium and the top coat material B4C of 160–200 μm thickness. The spray angle was varied from normal incidence to 60° with respect to the substrate normal. The effects of processing conditions on microstructure, mechanical properties and thermal load resistance were investigated by use of X-ray diffraction, optical microscopy, SEM, optical porosimetry, roughness- and adhesion-tests and thermal shock experiments in the electron beam test facility JUDITH. The thickness of the deposited B4C-coatings decrease to a minimum of 40 μm with increasing spray angle. Simultaneously the average roughness increases at a constant value of porosity. It could be stated, that the coatings, deposited at a larger angle, tend to exhibit a larger erosive attack pattern at slightly lower energy.