Grain refinement and mechanical property improvement in IN625 alloy deposited by in-situ hot rolling assisted laser directed energy deposition

• In-situ hot rolling (ISHR) was integrated with laser directed energy deposition (LDED) to refine IN625 alloy microstructure. • ISHR effectively suppressed columnar grain growth and promoted the formation of fine equiaxed grains. • The yield strength of the alloy was doubled while maintaining acceptable ductility. • Microstructural analysis revealed increased dislocation density and lattice rotation in the rolled samples. • ISHR significantly improved the anisotropy of mechanical properties in LDED IN625 alloy. A headache problem has recently been highlighted in the laser directed energy deposited (LDED) IN625 alloy, where columnar grains with a large size are prevalent due to the complex heat flow effect. Influenced by this, the LDED IN625 alloy generally shows a low strength and severe anisotropy of mechanical behavior, limiting their practical application. To address this, an in-situ hot rolling (ISHR) assisted LDED strategy was employed to fabricate the thin-wall part of IN625 alloy in this work. The results demonstrate that the introduction of ISHR during LDED can promote the formation of fine equiaxed grains, along with an increased dislocation density. Significantly, the yield strength (YS) of the alloy is doubled while keeping an accepted ductility, and the anisotropy of tensile properties is improved. Dislocation strengthening and refine grain strengthening are responsible for the enhancement of the YS, and the related strengthening contributions are calculated to be about 240 MPa and 260 MPa, respectively. In addition, in-situ electron backscatter diffraction (EBSD) results reveal that lattice rotation and the formation of low-angle grain boundaries are the main deformation features of the rolled sample. In brief, the present study provides a feasible pathway for removing the columnar grain structures and improving mechanical performance in additively manufactured alloy.