Additive manufacturing of Inconel 718-Copper alloy bimetallic structure using laser engineered net shaping (LENS™)

To understand processing ability and measure resultant interfacial and thermal properties of Inconel 718 and copper alloy GRCop-84, bimetallic structures were fabricated using laser engineering net shaping (LENS (TM)), a commercially available additive manufacturing technique. It was hypothesized that additively combining the two aerospace alloys would form a unique bimetallic structure with improved thermophysical properties compared to the Inconel 718 alloy. Two approaches were used: the direct deposition of GRCop-84 on Inconel 718 and the compositional gradation of the two alloys. Scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), X-ray Diffraction (XRD), Vickers microhardness and flash thermal diffusivity were used to characterize these bimetallic structures to validate our hypothesis. The compositional gradation approach showed a gradual transition of Inconel 718 and GRCop-84 elements at the interface, which was also reflected in the cross-sectional hardness profile across the bimetallic interface. SEM images showed columnar grain structures at the interfaces with Cr2Nb precipitate accumulation along grain boundaries and the substrate-deposit interface. The average thermal diffusivity of the bimetallic structure was measured at 11.33 mm(2)/s for the temperature range of 50 degrees C-300 degrees C; a 250% increase in diffusivity when compared to the pure Inconel 718 alloy at 3.20 mm(2)/s. Conductivity of the bimetallic structures increased by almost 300% compared to Inconel 718 as well. Such structures with designed compositional gradation and tailored thermal properties opens up the possibilities of multi-material metal additive manufacturing for next generation of aerospace structures.