Achieving impressive strength and mitigated anisotropy in high-power laser-arc hybrid additive manufacturing of stainless steel through tailored microstructures composition

Abstract

High-power laser-arc hybrid additive manufacturing (HP-LHAM) is beneficial to improving tensile properties and reducing anisotropy, but the mechanisms remain unclear. This work focused on the effects of parameters on microstructures, tensile properties, and anisotropy in HP-LHAM of stainless steel quantitatively. The HP-LHAMed sample exhibited a heterogeneous microstructure featuring fine grains in remelting zone (FGRZ) and coarse grains in melting zone (CGMZ). By observing the microstructure characteristic, it was determined that the δ-ferrite shape in CGMZ can be transformed under the impact of large pulsed current triggered solution heat treatment effect or high-frequency laser beam oscillation, while kept as strip shape in FGRZ. Furthermore, investigations demonstrated that the utilization of a high-power laser with beam oscillation not only led to a synchronous increase in strength and elongation, but also brought about a pronounced reduction in anisotropy. This results in an optimized horizontal yield strength (YS) of 363 MPa, which was superior to that of the as-deposited sample without laser beam (∼318 MPa). The corresponding YS anisotropy had decreased from 7.5% to below 2.0%. YS modeling analysis proved that the improved properties were primarily ascribable to fine-grain strengthening rather than solution or precipitation strengthening, because their contributions for the YS improvement were 166.6, 27.7, and 3.3 MPa, respectively. While for the anisotropy of tensile properties, the value of Taylor factor and range of FGRZ were the main factors, and the influence of the latter was more remarkable than the former. Two methods for improving tensile properties and reducing anisotropy were then proposed accordingly. These new findings will deepen the understanding and expand the application of HP-LHAM process in the preparation of large size components.