Microstructural changes in a laser solid forming Inconel 718 superalloy thin wall in the deposition direction

The microstructure variation of as-deposited Inconel 718 superalloy sample in deposition direction fabricated by laser solid forming (LSF) was investigated. It was found that the as-deposited microstructure was mainly consisted of predominant γ columnar dendrites directionally growing along the deposition direction. Primary dendrite arm space measurement revealed spaces of 11.5, 17.5 and 38.0 μm at the bottom, the middle and the top section of the LSF sample respectively. The result was further studied by comparing with the Kurz-Giovanola-Trivedi (KGT) dendrite growth model, which was in a reasonable agreement with the experimental result. The various microstructures and micro-segregation situations at different sections of the LSF sample, which were induced by the thermal accumulation during LSF process, were also carefully discussed.