Effects of Rotation Angle on Surface Morphology, Microstructure, and Mechanical Properties of Invar 36 by Laser Powder Bed Fusion

Abstract

The scanning strategy is one of the most influential parameters determining the forming quality, microstructure, and properties in the Laser powder bed fusion (LPBF) process. The optimized scanning strategy enables the transition from "passive adaptation to defects" to "active control performance", significantly contributing to the maximizing material properties. To investigate the scanning strategy, particularly the often overlooked impact of rotation angle on the surface morphology, microstructure, and mechanical properties of Invar 36 alloy fabricated by LPBF, three representative rotation angles: 0°, 67°, and 90° were selected in this work. The results indicate that the rotaion angle has a negligible influence on the type of microstructure established during LPBF processing: all samples display cell-shaped and strip-shaped substructures. However, the rotation angle significantly affects the surface morphology and mechanical properties. The findings reveal that adopting 0° and 90° rotation angles results in relatively poor surface finish and lack-of-fusion defects, whereas a 67° rotation angle leads to reduced surface roughness and improved relative density. A noticeable “edge effect” is observed at a rotation angle of 0°. Moreover, the sample fabricated using a 67° rotation angle exhibits the finest microstructure and the optimal combination of mechanical properties, with yield strength and ultimate tensile strength reaching 350.34 MPa and 501.03 MPa, and plastic deformation approaching 50%.

Keywords: Laser powder bed fusion, Invar 36, Rotation angle, Microstructure, Mechanical properties