In-situ microstructure control by laser post-exposure treatment during laser powder-bed fusion

Abstract

In-situ microstructure control is an important feature of laser powder-bed fusion (LPBF) that enables the tailoring of the mechanical behaviour of additively manufactured metallic parts. In this research, a novel method is introduced to control the formation of microstructure by laser post-exposure (PE) treatment during the LPBF process. Laser post-exposure treatment is a secondary laser scanning with significantly lower energy input, resulting in the development of uniform, uninterrupted, and elongated grains. This secondary laser scanning is conducted after the completion of the main laser scanning strategy on the loose powder and before spreading the new layer of powder. Using electron backscatter diffraction and optical microscopy, it has been found that while the average length of the elongated grains was 845 µm for a PE-treated sample, this value for the same sample in the absence of the PE treatment was 321 µm. Therefore, for the first time, an in-situ laser treatment has been reported for the microstructure control of LPBF-made parts. A printed part utilizing post-exposure may be comparable to directionally solidified products used widely in industries for enhanced creep and fatigue resistance.

Keywords

• Laser powder-bed fusion
• Laser post-exposure
• Microstructure control
• Directional solidification
• Elongated grain