Diffusion brazing of cast INCONEL 718 superalloy utilising standard heat treatment cycle

Abstract

The time required to ensure completion of the isothermal solidification process is the key in obtaining an intermetallic free and robust joint after diffusion brazing. In view of economic considerations, it is interesting to perform bonding process trials using standard heat treatment cycles. This paper addresses the effect of applying the standard heat treatment cycle including homogenisation, solution and double aging treatments on the microstructural and mechanical response of diffusion brazed IN718. A commercial Ni–7Cr–4·5Si–3·2B–3Fe (wt-%) brazing alloy was used as the interlayer. Results showed that bonds made with the standard homogenisation treatment, at 1100°C, exhibited a eutectic free joint centreline. After applying the standard solution and double aging treatment, a bond with a joint efficiency of 82% relative to base metal was obtained in terms of shear strength. Room temperature tensile properties and stress rupture properties of the diffusion brazed joint were better than the minimum requirement of the AMS5383 acceptance standard.

Keywords:

• Diffusion brazing
• Transient liquid phase bonding
• Cast IN718
• Standard heat treatment
• Isothermal solidification

M.P. gratefully acknowledges the support from Professor H. N. Han during his sabbatical leave in the Department of Materials Science and Engineering, Seoul National University.