Rivestimenti spessi di W su CuCrZr per applicazioni nei futuri reattori a fusione nucleare

The precipitation hardened CuCrZr alloy has been used in the past as a structural material for actively cooled plasma facing components of nuclear reactors (Tore Supra and JET) and selected as the heat sink material for divertor parts of the future International Thermonuclear Experimental Reactor (ITER) [1]. Because of its high melting point and good thermal conductivity, W is a promising material to use as protection (armour) for thermal shields made of CuCrZr. However, W-Cu joining is really challenging for the high thermal expansion mismatch between W and Cu alloys (alpha(Cu) approximate to 4 alpha(W)), the high elastic modulus and brittleness of W. Important requirements for high quality W-armours are low porosity and low impurity content. For realizing the joints, plasma spraying (PS) has been used for its simplicity, the possibility to cover complex and extended surfaces and the relatively low cost. An appropriate interlayer was optimized 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. It was possible to manufacture mock-ups for ITER by depositing up to 5-mm thick W-coatings on tubular substrates of CuCrZr (Fig.1), which were able to sustain a remarkable number of thermal fatigue cycles under high heat flux (up to 5 MW/m(2)) [2-4]. Microstructural and mechanical characterization confirmed the good properties [4,5].