Mechanical Properties of the W Coating and Interface of Vacuum-Plasma-Sprayed W–Ferritic Steel Joints Under Shear and Bending Loads

Vacuum plasma spraying (VPS) is a prospective technology for the fabrication of tungsten-coated ferritic steel (W-steel), which is the main candidate for plasma-facing components (PFCs) of fusion reactors. PFCs are sub-jected to harsh service environments; therefore, the mechanical properties of W-steel joints must be evaluated. However, detailed studies on the mechanical properties of W-steel joints are still limited because of the limited thickness of the tungsten-coating layer. In this study, high-grade W-steel joints were fabricated using a VPS system. The mechanical properties of the W coating and W-steel interface were evaluated using micro-double-notch compression and micro-cantilever bending tests. The ultimate shear strength of the interface area exhibited a large scatter (-0.84-3.54 GPa), which was similar to that of the W layer (-1.2-3 GPa) and higher than that of the reduced-activation ferritic/martensitic steel (F82H) substrate (-0.6 GPa). The bending test indicated that the interface exhibited good bending performance and that its nominal fracture strength was higher than that of the W coating, which may be attributed to the ductile nature of the F82H region at the interface. The fracture microstructure elucidated the importance of improving the mass densities of W coatings to improve the mechanical performance of vacuum-plasma-sprayed W-steel joints. Effective bonding of a W/F82H interface and the adjacent F82H substrate via VPS results in high strength and ductility of the interface area, and hence the W-steel joint, against shearing and bending loads.