Effect of overlap rate on recrystallization behaviors of Laser Solid Formed Inconel 718 superalloy

The effect of overlap rate on the residual stress, recrystallization nucleation location and the distribution of recrystallized grains of LSFed Inconel 718 superalloy were investigated. It is found that the as-deposited microstructures with different overlap rates have the similar characteristics including that columnar grains grow along the deposition direction. The overlap area possesses higher residual stress compared with the inner-pass area, and the position of peak residual stress is closer to previous pass. The increase in the overlap rate will broaden the variation range of the residual stress. During heat treatment, the recrystallization nucleation first occurs in the overlap area with the lower overlap rate, and then expands to both overlap area and inner-pass area paralleling with the increasing of the overlap rate. Although the overlap rate is only one of basic factors in the Laser Solid Forming process, it plays an important role in controlling residual stress distribution, material microstructure and mechanical properties. The higher overlap rate adopted, the finer and the more evenly distributed grains could be obtained through recrystallization for LSFed Inconel 718 superalloy.

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► The overlap rate brings very little change in the as-deposited microstructure.
► Overlap area has higher residual stress than inner-pass area.
► The higher overlap rate results in higher residual stress.
► Recrystallized nucleation location expands along with overlap rate increasing.
► The higher overlap rate could obtain finer and more evenly distributed grains.