Investigation of microstructure and mechanical properties of diffusion brazed boron carbide ceramics with Ni-Cr-Si-Fe-B-C filler alloy

This study investigates the mechanical properties and microstructure of boron carbide ceramic joints with Ni-Cr-Si-Fe-B-C filler, using vacuum diffusion brazing at temperatures from 1363 to 1423 K. The results of shear strength tests showed a 43.8% increase (from 39.44 to 56.73 MPa) as the temperature rose from 1363 to 1383 K, a 22.8% increase (from 56.73 to 69.56 MPa) from 1383 to 1403 K, and a 10.9% decrease (from 69.56 to 61.92 MPa) from 1403 to 1423 K. The sample brazed at 1403 K for 30 min showed the highest shear strength of 69.56 MPa. This increased strength is due to the higher fluidity of the molten filler alloy and enhanced interactions in the ceramic-metal system at elevated temperatures. The joint interface, interfacial phenomena, fracture surface, hardness, microstructure, and phases in different samples were analyzed. Fractography results indicate that shear strengths correlate with the ratio of removed areas from the ceramic on the fracture surface. The boron carbide part exhibited a mixed mode of brittle fracture. Successful joining and good strength at low temperatures are attributed to compounds like Fe2B, SiC, and Ni4B3. Higher temperature samples showed stronger peaks of these compounds and chromium borides, contributing to the higher strength observed. The study also reveals consistent results in the diffusion pattern of elements, elemental analyses, hardness values, and phases formed at the fracture surface.