Strength, microstructure and bonding mechanism of borosilicate glass-to-SA105 carbon steel seals

Abstract The bonding strengths, microscopic characteristics and fracture properties of borosilicate glass-to-SA105 carbon steel seals were investigated, and two different glass-to-metal bonding mechanisms were compared. First, a mechanical interlocking mechanism was found via precipitates formed from chemical reactions at the interface of the seal bonded to unoxidized SA105 carbon steel. Second, a transitional layer mechanism was proven by the dissolution of metal oxides, which was on the surface of preoxidized SA105 carbon steel, into the glass. The bonding strength results showed that both mechanisms effectively contributed to the joining of dissimilar phases, but the effect of the latter mechanism was more prominent than that of the former mechanism. Various microstructures and chemical compositions of the surface oxide scales were obtained by applying different preoxidation conditions to SA105 carbon steel. Additionally, different sealing interfaces were reported through this process. The width of the interfacial transitional layer ranged from 0.5 μm to 1.5 μm, and the strength of the seal was closely related to this width. The sealing of SA105 carbon steel that was preoxidized at 800 °C for 30 min with a moderate width of the transitional layer had an optimal shear strength of 25.4 MPa. However, a wide transitional layer composed of the remaining oxide scales deteriorated the strength of the seal. In addition, fracture analysis of the seals after the shear test was conducted, and the intrinsic correlations between the macroscopic shear strength and microscopic bonding mechanism were established. The present work should provide a reference for the characterization of bonding strength in joining dissimilar materials.