Effect of powder layer thickness on the microstructure and properties of Inconel 625 superalloy manufactured by selective laser melting

The microstructure and mechanical properties of Inconel 625 alloy formed by selective laser melting (SLM) with various powder layer thicknesses were methodically examined. The formation mechanisms of crystal texture and the contributions of different strengthening mechanisms to yield strength were deeply analyzed. The molten pool of SLM-ed alloy was primarily constituted by epitaxially grown columnar dendrites and slight cellular structure, with the Laves phase distributed in interdendritic areas. Cube texture ({001}<100>) and Rotated Goss texture ({110}<110>) were the main texture types in the alloy, formed by dendrites growing epitaxially along <001> direction and perpendicular to <011> direction, respectively. Both the content of the Laves phase and the primary dendrite arm spacing (PDAS) increased as a result of escalating laser power and diminishing scanning speed. Higher laser power and lower scanning speed also resulted in raised fractions of both textures and reduced Taylor factors in the SLM-ed alloy. Compared with those of 30 μm, the SLM-ed alloy with a layer thickness of 50 μm exhibited lower contents of the Laves phase and both textures, smaller PDAS as well as higher Taylor factors. The theoretically calculated yield strengths of the SLM-ed alloy with distinct layer thicknesses were consistent with the measured data. Higher yield strengths of the alloy with a layer thickness of 50 μm were mainly ascribed to the improvement of solid solution strengthening and grain boundary strengthening.