Tailoring microstructure and mechanical property of laser powder deposited Inconel 718 superalloy via hybrid processing strategies

Customized tailoring of the microstructure and mechanical properties is a longstanding and challenging requirement for the high-performance implementations of laser additive manufacturing technology in the aircraft industry. In this study, two sets of processing parameters were alternated layer by layer, forming hybrid processing strategies. Thin-wall builds of Inconel 718 superalloy were produced by laser powder deposition process to preliminarily study the effect of hybrid processing strategies on tailoring the microstructure and mechanical properties. The results indicate the hybrid processing strategies have a distinct influence on the crystal growth behavior, grain orientations and sizes, precipitations and associated tensile strengths. Under the bidirectional scanning pattern, the hybrid processing strategy could effectively tailor the macroscale orientation of coarse zigzag microstructure through adjusting and disturbing the primary-secondary dendritic arms alternate growth behavior of columnar crystals. The columnar crystal trunk size exhibits a banded feature with large value in low-velocity deposition layer and small value in high-velocity layer. Under the unidirectional scanning pattern, the hybrid processing strategy can distinctly balance the size and aspect ratio of oriented fibrous grains. The strong texture of microstructure acts as an important contributor to determine the fracture behavior and associated ultimate tensile strength. Comparing to the single processing strategies, the hybrid processing strategies show little effect on the ultimate tensile strength with a slightly increased anisotropy under bidirectional scanning pattern, while distinctly improve the ultimate tensile strength with a reduced anisotropy under unidirectional scanning pattern, showing the potential to tailor the microstructure distribution and mechanical properties with customized high-performance requirements by purposely adjusting the hybridization of processing parameters.