Induction brazing of Inconel 718 to Inconel X-750 using Ni–Cr–Si–B amorphous foil

Abstract

Induction brazing of Inconel 718 to Inconel X-750 using Ni–7Cr–3Fe–3.2B–4.5Si (wt.%) foil as brazing filler metal was investigated. Because of the sensitive responses of induction brazing, the microstructural evolution of joint interfaces can be effectively realized. Brazing was conducted at the temperature range 1373–1473 K for 0–300 s in a flowing argon environment. Both interfacial microstructures and mechanical properties of brazed joints were investigated to evaluate joint quality. The optical and scanning electron microscopic results indicate that good wetting existed between the brazing alloy and both Inconel 718 and Inconel X-750. The diffusion of boron and silicon from brazing filler metal into base metal at the brazing temperature is the main controlling factor pertaining to the microstructural evolution of the joint interface. The element distribution of Cr, Fe, Si, Ni and Ti was examined by energy dispersive X-ray analysis. It was found that silicon and chromium remain in the center of brazed region and form brittle eutectic phases, boron distribution is uniform across joint area as it readily diffuses from brazing filler metal into the base metal. The influence of the heating cycle on the microstructures of the base material and holding time on the mechanical properties of the brazed joints were investigated. It was found that the microstructures of the base material were not affected by the rapid heating and cooling cycle of induction processing, but the shear strength increased with increasing brazing time. Results show that excellent joint shear strengths of as high as about 503 MPa were obtained when processed at approximately 1423 K for 300 s.