Laser powder bed fusion (LPBF), a typical metal additive manufacturing (MAM) process, generates large thermal gradients and rapid cooling rates, making it challenging to fully understand the relationship between nano-scaled solidification microstructure and process parameters. This study aims to uncover the nano-scaled solidification microstructure characteristics of 316L stainless steel (SS) produced through LPBF. A deeper understanding of microstructural development is crucial for fabricating high-performance materials by effectively controlling the AM process.
1. Introduction
Laser powder bed fusion (LPBF) is currently the most versatile metal additive manufacturing (MAM) process, enabling the production of complex parts without the design limitations of traditional manufacturing methods. The rapid and repeated thermal cycles create intense thermal gradients, leading to metastable chemical, structural, and mechanical states, resulting in metallurgical defects that compromise material properties. Extensive research of LPBF-processed 316L SS has been conducted to improve the mechanical properties and highlight the need to correlate different microstructural features with the manufacturing process. Most studies have focused on characterizing microstructures from macro to sub-micrometer scales, with few investigating features at the nano or atomic levels. Therefore, this study aims to explore these nano/atomic scale microstructural features to better understand the relationship between solidification microstructure and process parameters.
2. Experiment
The nominal composition of the 316L SS powder was 18Cr-14Ni-2.5Mo-0.03C (wt.%), and the powder size was under 53µm. LPBF fabrication was conducted using a 3D printer (EOSM290, EOS GmbH, Germany) equipped with a Yb-fiber laser by the “X-scan strategy,” i.e., the laser beam was scanned bidirectionally along the X-axis without rotation.