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Abstract: 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 38.0μm 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. [Copyright &y& Elsevier]

Abstract: The microstructure and residual stress of laser rapid formed (LRFed) nickel-base superalloy Inconel 718 was investigated. The as-deposited microstructure of an LRFed Inconel 718 alloy is composed of columnar dendrites growing epitaxially along the deposition direction, and the columnar dendrites transformed to unevenly distributed equiaxed grains after annealing treatment at high temperature. Residual stress evaluation in microstructure scale by Vickers micro-indentation method indicates that the residual thermal stress is unevenly distributed in the LRFed sample, and it has a significant effect on the recrystallization during solution annealing treatment. The residual stress is introduced by rapid heating and cooling during laser rapid forming. There is an alternative distribution between high residual stress regions and low residual stress regions, within a single deposited layer, resulting in a similar distribution of recrystallized grain size. [ABSTRACT FROM AUTHOR]