Investigation on the microstructure of W-coated low-activation alloy V-4Cr-4Ti

Microstructures of vacuum plasma sprayed (VPS) and brazed W on NIFS-HEAT-2 were studied by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). During the VPS process, growth of grains perpendicular to the interface was prominent. The blocky Ti-oxides, which have a strong effect on the mechanical properties before and after irradiation, were dissolved in the interface region of NIFS-HEAT-2. Understanding the effect of heat treatment (namely, post-coating heat treatment) on W-coated materials is important to reduce the irradiation induced hardening effects on the materials. After a heat load of about 5 MW/m2 (∼16 cycles), the surface of VPS-W has a very fine rough structure but no prominent cracks due to thermal heat loads were detected.