The selective laser melting of high temperature alloys is of great interest to the aerospace industry as it offers the prospect of producing more complex geometries than can be achieved with other manufacturing methods. In this study, the microstructure of the nickelbased superalloy, CM247LC, has been characterised following selective laser melting and after a post deposition heat-treatment below the γʹ solvus temperature. In the as-deposited state, scanning electron microscopy with electron backscatter diffraction revealed a fine, cellular microstructure with preferential alignment of <100> along the build direction. A high dislocation density was seen at the periphery of the cells, indicating substantial localised deformation of the material. Fine primary MC carbides were also observed in the inter-cellular regions. High-resolution transmission electron microscopy identified the occurrence of very fine γʹ precipitates, approximately 5 nm in diameter, dispersed within the gamma phase. After heat treatment, the elongated cell colonies were observed to partially coalesce, accompanied by a decrease in dislocation density, producing columnar grains along the build direction. Cuboidal γʹ precipitates approximately 500 nm in diameter were observed to form in the recrystallised grains, accompanied by larger γʹ precipitates on the grain boundaries.

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In this study, bulk and multifoil diffusion couple experiments were conducted to examine the interdiffusion process in Ni-Pt and Co-Pt binary alloy systems. Inter-, intrinsic-, and tracer-diffusion coefficients at different temperatures, and as a function of the composition, were estimated by using the experimental data. Results show that in both the alloy systems, Pt is the slower diffusing species, and hence the interdiffusion process is controlled by either Ni or Co. The thermodynamic driving force makes the intrinsic diffusion coefficients of Co and Ni higher in the range of 30-70 at.%. The low activation energy for Co and Ni impurity diffusion in Pt compared with Pt in Ni and Co indicates that the size of the atoms plays an important role. The vacancy wind effects on the diffusion process are examined in detail, and it was demonstrated that its contribution falls within the experimental scatter and hence can be neglected.

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