Brazing of high-nitrogen steel to Al0·3CoCrFeNi using a BNi-2 filler: Microstructure, mechanical properties, and corrosion resistance

Abstract

Studies that focus on brazing high-nitrogen steel (HNS) to high-entropy alloys (HEAs) are currently limited. In this study, the HEA Al0·3CoCrFeNi was successfully brazed to HNS using a commercial BNi-2 filler at 1080–1140 °C. The microstructure and shear strength of the Al0·3CoCrFeNi/HNS brazed joints were observed and evaluated. The typical microstructure of the brazed joint was HNS/infiltration layer/reaction layer/Ni(s,s) (containing NiAl3)/reaction layer/infiltration layer/Al0·3CoCrFeNi. The higher brazing temperature and longer holding time promoted the diffusion of B as a brazing seam with homogeneous Ni(s,s), and more intergranular Cr-rich borides formed in the base materials. The optimized shear strength attained 549.2 MPa after the joint brazed at 1120 °C for 15 min, and ductile fracture occurred in the reaction zone. The insufficient and excessive diffusion of B resulted in residual Cr–B compounds in the brazing seam and excess borides in the HNS, respectively, which negatively affected shear strength. All the joints showed poor corrosion resistance following immersion in a 3.5 wt% NaCl solution because the excess Cr-rich compounds resulted in decreased Cr content in the surrounding matrix. Therefore, Ni-based fillers without B were more suitable for obtaining Al0·3CoCrFeNi/HNS joints with a favorable corrosion resistance.