Development of mechanical properties of plasma-facing components of blanket utilizing selective laser melting techniques

Water cooled ceramic breeding blanket is a key component of the China Fusion Engineering Test Reactor. As the plasma-facing components (PFCs) of Blanket exposed to plasma directly, the manufacturing process of reduced activation ferritic/martensitic (RAFM) steel faces severe challenges. In this study, RAFM steel PFCs was fabricated using selective laser melting, and the impact of heat treatment processes on its microstructure and properties was thoroughly analyzed. The results indicated that tempering after normalizing (NT) most effectively enhanced the comprehensive mechanical properties of RAFM steel at room temperature (σb = 668.8 MPa, δ = 16.1%). The original RAFM steel exhibited a pronounced checkerboard scanning feature with cubic texture, characterized by an orderly distribution of coarse lath martensite and fine acicular martensite. The checkerboard feature disappeared and grains tend to be uniform after heat treatment. The dense dislocation networks appeared and carbides precipitated in original specimens, which exhibited dislocation strengthening was the primary mechanism. However, dislocations began to release and carbides precipitated along the lath boundaries or within the martensitic grains with the recrystallization process after thermal treatment. Precipitations were mainly Cr-rich M23C6 carbides and Ta, V-rich MX carbonitrides via detected. And the dominant mechanisms were precipitation and fine grain strengthening in NTed, HIPed and NHed specimens. Overall, the 740 °C tempering after 980 °C normalizing heat treatment processes were effective in enhancing the microstructure and comprehensive mechanical properties of RAFM steel. This work provided prominent guiding values for high-performance manufacturing of the first wall on fusion reactors.