On the feasibility to obtain CuCrZr alloys with outstanding thermal and mechanical properties by additive manufacturing

Abstract

The CuCrZr alloy combines high thermal conductivity and mechanical strength with stability at high-medium temperatures, making it a promising heat sink material for the EU-DEMO divertor and limiters. Additive Manufacturing (AM) technologies have proven effective in developing complex-shaped components with almost no constraints on geometry and minimal machining and welding requirements. This makes them particularly suitable for the production of heat exchangers featuring complex cooling channels with intricate inner structures.This study demonstrates the feasibility to obtain dense CuCrZr via Electron Beam Powder Bed Fusion (EB-PBF) with high thermal conductivity and enhanced mechanical strength compared to conventional routes. Gas atomization was used to produce spherical powders with a composition close to ITER specifications. By optimising the EB-PBF process parameters, relative density values of 99.7 % were achieved after HIP treatment, that removes the eventual residual porosity. The results underscore the importance of meticulous powder manufacturing to mitigate oxidation and microstructural defects in the final components. Achieving high relative densities in the EB-PBF process requires a focus on adopting high-energy absorption rates in the powders. This strategy can be accomplished by reducing the scanning speed and consequently the building rate of the process. The microstructural characterization revealed a complex hierarchical microstructure composed of grains and grain boundaries, solidification-enabled cellular-like subgrains elongated along the building direction and an ultra-fine precipitate state (already present in the as-built condition) mainly consisting of Cr-rich nanoprecipitates, although Zr-rich precipitates were also found at the melt pool boundaries. The thermal conductivity, hardness, mechanical strength at room temperature and high-medium temperatures were measured and correlated with the EB-PBF process parameters and the microstructure obtained after HIP treatment. The results indicate that it is possible to obtain CuCrZr with improved mechanical behaviour compared to conventional manufacturing technologies, while maintaining the thermal conductivity requirements for EU-DEMO.