Thermal and mechanical properties of infiltrated W/CuCrZr composite materials for functionally graded heat sink application

Functionally graded tungsten/copper composite materials are considered as interlayer material for the water-cooled divertor target of fusion reactors consisting of a tungsten base armor and a copper alloy heat sink. The W/Cu composite interlayer is supposed to reduce the thermal expansion mismatch and to strengthen the heat sink. A critical drawback of this composite is loss of strength at elevated temperatures owing to the softening of the copper matrix. To solve this problem, we developed a novel tungsten/copper composite using precipitation-hardened Cu1CrZr alloy instead of pure copper. To this end, a fabrication route based on melt infiltration into a tungsten skeleton was established. Comprehensive characterizations and tests were performed on the specimens of three compositions (30, 50 and 70 vol.% of tungsten) at temperatures of 20, 300 and 550 C. In this paper, extensive data of thermal and mechanical properties are presented. It turned out that the composites p ossess a strongly enhanced strength compared to the W/Cu composites and unreinforced alloy. The tensile behavior exhibits a significant hardening effect even for small W content while the rupture strain is decreased as well. Nevertheless, the composites show a still acceptable ductility for W content up to 50 vol.%. The composite of higher W content becomes fully brittle. Graded composites were also produced. Metallographic analysis confirms a good bonding between the layers. The thermal conductivity and thermal expansion data exhibit a typical rule-of-mixture behavior indicating a high quality of the materials.