Effect of hatch spacing and laser remelting on the formation of unique crystallographic texture of IN718 superalloy fabricated via laser powder bed fusion

This study investigated the effects of hatch spacing and laser remelting on microstructure and growth texture of IN718 superalloy fabricated via laser powder bed fusion (LPBF) based on the bidirectional scanning strategy. A crystallographic lamellar microstructure (CLM) with a 〈0 0 1〉 // the building direction (BD) growth texture in the center layer was obtained. The increase of hatch spacing can influence the intensity of 〈0 0 1〉 // BD growth texture in the center layer and deflect the 〈0 1 1〉 oriented dendrites in the overlapping layer to the scanning direction. Meanwhile, with the increase of hatch spacing, the primary dendrite arm spacing increases, and morphologies of the interdendritic precipitated Laves phases change from discrete dots to chains. The selection effect of laser remelting was discovered, which works as the “selector” for preferential orientation grains. Through several times of interlayer laser remelting, the grains with preferential orientations are selected by competitive growth. Laser remelting can also eliminate the stray grains and dendrites on the top of the molten pool and improve the heat input. Therefore, the epitaxial growth of 〈0 0 1〉 // BD columnar grains in the center layer is promoted. Based on the optimized hatch spacing and the laser remelting process, a 〈0 0 1〉 // BD near directional solidification structure is obtained.