Investigation of 316L microstructure evolution mechanism and mechanical properties in dual-laser powder bed fusion with controllable remelting time interval

Abstract

Remelting has a significant effect on controlling microstructure and enhancing properties of components prepared by laser powder bed fusion. In order to reveal the mechanism of the effect of remelting time intervals, this study employed a dual-laser powder bed fusion equipment to ensure precise and controllable time intervals of remelting. The effects of intervals (2 ms, 5 ms, and 50 ms) on substructure morphology, microstructure and mechanical properties of 316L were analyzed. The results indicate that the grain size ranged from 13.03 μm to 26.55 μm due to the influence of initial temperature at different remelting intervals on grain size. Additionally, the composition ratio between columnar and cellular substructure varies with the time interval, which greatly influences mechanical properties. Longer intervals favor columnar substructures in high-temperature gradients, and dislocation motion is impeded, leading to an increased strength of up to 689.6 MPa. Shorter intervals promote cellular substructures in low-temperature gradients, and dislocations move smoothly along the boundaries of substructure, leading to an elongation of up to 49.3 %. Therefore, a novel method for controlling microstructure and properties is provided in this study utilizing the precise controllable remelting time intervals of dual-laser powder bed fusion.

Keywords

• Selective laser melting
• Multi-beam
• Dislocation cell
• Grain growth
• Microstructure evolution