Effect of laser power on defect, texture, and microstructure of a laser powder bed fusion processed 316L stainless steel

TLDR

Laser powder bed fusion of 316L stainless steel was examined to determine how laser power influences defect formation, microstructure, constituent phases, and crystallographic texture. Specimens were fabricated at laser powers from 380 to 200 W (scan speed 300 mm s⁻¹) and evaluated by synchrotron micro‑CT for pore characteristics, synchrotron X‑ray diffraction for texture and phases, and metallography for melt‑pool shape and grain orientation. Lowering laser power increased porosity linearly from 0.13 % to 0.88 %, refined cellular spacing from 1.5 µm to 0.75 µm, and shifted texture from strong (200) to random, yet 200 W still produced nearly fully dense parts, demonstrating that microstructure can be tuned within an optimal porosity range.

Abstract

The effect of laser power on defect characteristics, microstructure development, constituent phases, and crystallographic texture was studied on a laser powder bed fusion (L-PBF) processed 316L stainless steel. A series of specimens was additively manufactured as a function of laser power ranging from 380 to 200 W with a fixed scan speed of 300 mm/s. The density, size, shape, and orientation of pores in as-printed L-PBF cylinders were characterized using high-resolution synchrotron X-ray computed microtomography with a 0.65 μm resolution. The changes in the texture and phases were investigated using high-energy synchrotron X-ray diffraction. The melt pool shape and grain size/orientation were also analyzed using metallography. The results show that the porosity increases linearly from 0.13 to 0.88% with the decrease in laser power. However, even with a decrease in laser power by about half and corresponding seven-fold increase in porosity, the 200 W case can still be considered as nearly fully dense. On the other hand, with the same decrease in the laser power, the cellular spacing was refined from 1.5 to 0.75 μm and the texture changed from strong (200) to random. Therefore, within an optimal porosity range, it is feasible to manipulate microstructure significantly using the control of laser power.