Exploring bonding temperature variations in diffusion brazing of B4C ceramics with Ni-Cr-Si-Fe-B interlayer: Mechanical and microstructural analysis

This study examines the impact of the bonding temperature parameter on the quality of diffusion brazing joints of B4C 4 C ceramics using a Ni-Cr-Si-Fe-B interlayer. Various factors including shear strength, hardness, microstructure, interfacial phenomena, elemental diffusion patterns, formed compounds and phases, and fracture surfaces of the samples were analyzed and compared. The brazed sample at 1110 degrees C for 1/2 h exhibited the highest shear strength of 62 MPa. Increase of the bonding temperature to the optimum level (1090-1110 degrees C) enhances the fluidity of the molten interlayer, facilitating its diffusion into the porosities of the ceramic components. This increase also promotes higher interactions within the system, creating favorable conditions for element diffusion. However, surpassing the optimum temperature (1110-1130 degrees C) may lead to increased destructive reactions and intensify the impact of the coefficient of thermal expansion (CTE) mismatch, resulting in residual stresses and a subsequent decrease in bond strength. The excessive increase in the bonding temperature (1130-1150 degrees C) can lead to the excessive fluidity of the molten interlayer, potentially causing effusion onto the joint's fixture and damaging the samples. The results indicate the formation of various compounds between the elements of the interlayer and carbon and boron elements, including SiC, Ni4B3, 4 B 3 , CrB2, 2 , Fe2B, 2 B, Ni6Si2B, 6 Si 2 B, and B2Fe3Ni3, 2 Fe 3 Ni 3 , at the fracture surface of the sample bonded at 1110 degrees C. The more substantial peaks of these compounds, compared to other samples, could be a reason for the higher strength of this particular sample.