Influence of Nano-Sized SiC on the Laser Powder Bed Fusion of Molybdenum

Abstract

Consolidation of pure molybdenum through laser powder bed fusion and other additive manufacturing techniques is complicated by a high melting temperature, thermal conductivity and ductile-to-brittle transition temperature. Nano-sized SiC particles (0.1 wt%) were homogeneously mixed with molybdenum powder and the printing characteristics, chemical composition, microstructure, mechanical properties were compared to pure molybdenum for scan speeds of 100, 200, 400, and 800 mm/s. The addition of SiC improved the optically determined density and flexural strength at 400 mm/s by 92% and 80%, respectively. The oxygen content was reduced by an average of 52% over the four scan speeds analyzed. Two mechanisms of oxygen reduction were identified as responsible for the improvements: oxidation of free carbon and the creation of secondary phase nanoparticles. This study illustrates the promising influence of nanoparticle additions to refractory metals in laser powder bed fusion.

Laser Powder Bed Fusion of Molybdenum and Mo-0.1SiC Studied by Positron Annihilation Lifetime Spectroscopy and Electron Backscatter Diffraction Methods

“…The EBSD IPF maps of the pure molybdenum and Mo-0.1SiC specimens with crystallographic textures are shown in Figure 4 and Figure 5 , respectively. As mentioned in our previous work [ 21 ], a significant amount of porosity plagued the prints of pure molybdenum and this can easily be seen even at the scales shown. Porosity was significantly reduced in the Mo-0.1SiC specimens.…”

“…This work will report the results of EBSD texture and grain boundary analysis along with PALS measurements. The results of mechanical testing, chemical composition, and optically determined density analyses, and scanning and transmission electron microscopy coupled with energy dispersive X-ray spectroscopy were presented in our previous paper [ 21 ].…”

“…This is mirrored in the Mo-0.1SiC specimens, where the expected trend is inversely related to scan speed after the 200 mm/s scan speed. From our previous research, it is known that, at the same processing parameters, the Mo-0.1SiC system experiences considerably more energy input than the pure molybdenum, and the differences with scan speed are more emphasized [ 21 ]. The differences between the grain sizes of pure molybdenum and Mo-0.1SiC demonstrate that the effect of the silicon carbide additions is more influential at lower scan speeds.…”

“…The pure molybdenum and Mo-0.1SiC specimens used in this study were consolidated in the same manner as described in our last paper [ 21 ]. One cylindrical specimen, 15 mm in diameter and 5 mm in height, was produced for each laser scan speed of 100, 200, 400, and 800 mm/s.…”

“…This work expands on the microscopy and mechanical testing of the LPBF of pure molybdenum and molybdenum with a dilute addition (0.1 wt%) of silicon carbide (Mo-0.1SiC) [ 21 ] by applying texture, grain boundary, and crystallographic orientation analysis through electron backscatter diffraction (EBSD) and microstructural analysis on the atomic-scale via PALS measurements. Literature reviews provide little evidence that PAS techniques have seen expansive use in characterizing AM materials [ 22 , 23 ]; however, their usefulness in identifying associated microstructural features should be expected.…”