Kin-Ling Sham1 Hahn Choo1 Xianghui Xiao2 Manyalibo Matthews3 Elena Garlea4

1, University of Tennessee, Knoxville, Knoxville, Tennessee, United States
2, Argonne National Laboratory, Argonne, Illinois, United States
3, Lawrence Livermore National Laboratory, Livermore, California, United States
4, Y-12 National Security Complex, Oak Ridge, Tennessee, United States

Fundamental understanding of the effects of processing parameters on various as-printed material characteristics, such as component dimensions, grain size/morphology/orientation, and defect density/distribution, is essential for critical advances in the development of structural or functional 3-D printed items. A systematic study on powder bed fusion (PBF), selective laser melting (SLM) 3-D printing process has been conducted to investigate the role of volumetric energy density (VED) in as-printed material characteristics. However, the consideration of only the VED (a thermodynamic parameter) will not accurately depict the complex heat and mass transport phenomena, their influence on the melt pool geometry, and, in turn, the development of microstructure and defects. Therefore, a processing-parameter matrix was created covering a wide range of VEDs with a series of iso-VED cases with varying combinations of power and speed. For example, under a same VED condition, comparisons between high power/high speed cases and low power/low speed cases were made for multiple iso-VED cases. In this study, the laser-beam power was varied from 140 to 380 W, while laser scan speed was also varied from about 75 to 1200 mm/s at each respective laser-beam power using 316L stainless steel as a model system. Using synchrotron x-ray microtomography, quantitative analysis of defects (pores, microcracks, and lack-of-fusion defects) was performed and correlated to the microstructure development as a function of the laser power, scan speed, and the VED. The correlations among 3-D printing parameters, their influence on solidification process, microstructure development, and defect characteristics will be discussed. More specifically, in addition to the general understanding of the role of VED inputs during an SLM process, the effect of laser power and scan speed within each subset of iso-VED cases will be discussed in terms of the physics of melt pool behavior and its correlations to the development of grain structure (i.e., size, shape, and orientation) and pore/crack characteristics (i.e., count, size, aspect ratio, and volume fraction). [A portion of this work was performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344. The abstract is released under LLNL-ABS-740854.]