Characterization of Bonded Zone and Evaluation of Cracking in Vacuum Brazed Zircaloy-4 and Stainless Steel-316L Joint

Brazing of two dissimilar structural materials; Zircaloy-4 and SS-316L was performed at 900°C under high vacuum conditions. The metallic glass ribbons (Zr₅₅Cu₃₀Al₁₀Ni₂Fe₃-at.%) of 30 μm thickness, were used as an interlayer. The bonded region was characterized by scanning electron microscope (SEM), energy dispersive spectroscope (EDS) and microhardness testing. The metallurgical bond formation was due to compositional changes in the molten interlayer and later on its subsequent solidification. Assessment of the bonded zone (BZ) revealed three distinct regions (Region-I, Region-II and Region-III). Diffusion transformation was observed in Region-I and Region-III which were interface with base alloys SS-316L and Zircaloy-4 respectively. However, Region-II at the middle of the BZ was composed of isothermally and athermally solidified portions. The highest values of Microhardness were observed in Region-III which was due to the presence of hard phases. Moreover, a crack parallel to BZ was observed in Region-III and was attributed to differential contraction of base alloys during cooling. Maximum shear stress acting on the BZ was calculated and correlated to the brittle phase cracking.