Characterization of ductile nano-TiC dispersed V4Cr4Ti/RAFMs solid diffusion joint for nuclear fusion reactor application

Reduced activation ferrite/martensite (RAFM) steel and V4Cr4Ti alloy are candidate structural materials applicable for blankets with various coolants for fusion reactor. In order to combine their advantages, a solid-state diffusion bonding bimetallic plate was designed to provide for high-temperature strength and neutron-irradiation resistance from the vanadium alloy and corrosion-resistance from the steel. However, brittle intermetallic and carbide layers can be formed during the high-temperature diffusion process, which is detrimental to the mechanical properties of the joint. To understand the mechanisms for a ductile joint, the diffusion bonding was performed at different temperatures by hot isostatic pressing (HIP). Various methods were used for the interfacial analysis, together with shear mechanical test and Vickers hardness test across the interface. The interfacial intermetallics differ significantly from each other with different bonding temperatures. Brittle sigma-(Fe, V) intermetallic and continuous V2C carbide layer could be avoided by optimizing the diffusion parameters. The joint bonded at 850 degrees C shows the optimal ductility with highest shearing strength value of 240 MPa, resulting from the synergetic effects. The dispersed TiC nanoparticles formed at interface would play an important role to improve the mechanical performances of the V4Cr4Ti/CLF-1 joint. Besides, no continuous thick carbides or sigma- (Fe, V) layer, finer grains in the decarburization layer and the ultra-fine recrystallization grains of the vanadium alloy around the interface are all helpful for joint performance improvement.