Low-activation joining methods for cWC and RSBs on steel for nuclear applications

Abstract

Cemented tungsten carbides (cWCs) and reactive sintered borides (RSB) are novel radiation-dense materials that are recent candidates as reactor shielding for compact spherical tokamaks (cST). This work investigates the use of pressure-less sinter-fusing methods for joining dissimilar materials for use in activating environments. Pressure-less sinter-fusing shows promise as a relatively non-invasive joining method for dissimilar materials, and it can be performed in an inert atmosphere or under vacuum. Sinter-fusing as a method for joining low-activation cWC and RSB materials to mild steels was investigated using various braze alloy mixtures as a paste and metal foils. A selection of low-activation braze alloys was investigated to join cWC and RSB to steel using sinter-fusing at 1300 °C in Ar for 2 h. Low-activating braze alloys were based on Cu and Fe as the major components with additions including Cr, Zr, Ti, C, B and Si as minor components. SEM-EDX was used to assess the quality of bonding and diffusion of the braze compounds post-sintering. The Vickers hardness mechanical test was carried out for the base materials and the joint interface, and the fracture toughness values were calculated from the hardness data. Results show that both brazing paste and foils have achieved well joints with no cracks and pores, but Cu foil-based joints shown superior to that of brazing paste concerning their mechanical properties.