Microstructure of additive manufactured materials for plasma-facing components of future fusion reactors

Two metallic materials considered for the divertor in fusion reactors are manufactured by powder bed fusion through electron beam melting: tungsten as armor of plasma-facing components and an age-hardenable CuCrZr alloy as heat sink material for the divertor. Cuboids are additively manufactured from both materials, and cross sections containing the build direction are characterized by electron backscatter diffraction. A peculiar heterogeneity is observed in the microstructure of tungsten and traced to the scanning strategy. Large columnar grains along the building direction with slight outward inclination are seen on both sides of the cross section i.e. where grains are observed in viewing planes perpendicular to the printing direction. Grains appear only slightly elongated in the center; neither their entire length nor their inclination is detected when the plane of view contains the printing direction. Many incidental twin boundaries are identified in the CuCrZr alloy; their occurrence is rationalized by the presence of an almost perfect fiber texture. Additionally, X-ray computed tomography confirmed the low porosity of the CuCrZr specimen.