Joining Inconel 718 and GRCop42: A framework for developing transition compositions to avoid cracking and brittle phase formation

Abstract

Distinct regions of high temperature strength and high thermal conductivity are required for components such as combustion chambers. Inconel 718 and GRCop42 are commonly used for such components. However, the bimetallic joining of these alloys has been shown to result in a liquid miscibility gap at the interface, which at select compositions can lead to brittle phase formation and cracking. In this work, CALPHAD modeling is used to predict regions of brittle phase formation in the Inconel 718–Ni–GRCop42 and Ni–Cu GRCop42 multi-component ternary systems, with experimental validation of the modeling provided by arc melting. Through characterization of arc melted sample microstructure combined with CALPHAD modeling, the solidification paths throughout the system are elucidated and a brittle phase and crack free compositional region is identified. Based on these results, a compositionally graded path consisting of two transition compositions is identified. Powder Laser Directed Energy Deposition is used to fabricate the Inconel 718–GRCop42 joint with the identified transition compositions, and the joint is subject to characterization in terms of composition profile, defects, grain morphology, present phases and microhardness. Results confirm the transition compositions circumvent brittle phase formation found in bimetallic Inconel 718–GRCop42 joints, thus overcoming the thermodynamic barrier of bimetallic joining.