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Mock-ups of thermal shields for international thermonuclear experimental reactor (ITER) have been manufactured by depositing 5-mm-thick W coatings on a CuCrZr alloy (ELBRODUR®). Coatings, made by controlled atmosphere plasma spray technique, have low porosity and excellent thermal fatigue resistance under high heat flux. Their structure has been investigated by scanning electron microscopy (SEM), scanning tunnel microscopy (STM), energy dispersion spectroscopy (EDS) and inductively coupled plasma (ICP) analysis. In spite of the remarkable thermo-mechanical properties of coatings, the present work evidenced some flaws (small cracks, unmolten W particles and presence of Ni in the external layers). Quality of coatings may be improved by strictly controlling purity and granulometry of sprayed W powders and some process parameters.

Mock-ups for the International Thermonuclear Experimental Reactor(ITER) were manufactured by depositing W coatings on tubular substrates of CuCrZr alloy via plasma spraying. An appropriate interlayer (of Ni, Al and Si) was optimised to increase the adhesion of W on the Cu alloy and to provide a soft interface with intermediate thermal expansion coefficient for better thermo-mechanical compatibility. The distribution of chemical elements in the layered interface and in the coating was investigated by energy dispersive spectroscopy (EDS), XPS and AES in the as-prepared material and after heat treatment of 24 h at 823 K. Moreover, the external W layer was examined by inductively coupled plasma emission spectrometry(ICP-ES). The results showed that the as-prepared material does not exhibit macro-porosity. The layers forming the interface do not exhibit any long-range diffusion of the chemical species from layer to layer during the deposition process. The heat treatment does not seem to cause long-range migration of Al and Ni into the W coating. The presence of Ni (0.4 wt%) in the as-deposited external W layer as shown by ICP-ES is only due to the low purity (commercial grade) of W powders used in spraying operations. It can be eliminated by using W powders of higher purity in the deposition process.