In-Situ Reduction of Mo-Based Composite Particles during Laser Powder Bed Fusion

Suxia Guo,Weiwei Zhou,Zhenxing Zhou,Wei Luo,Naoyuki Nomura,Yuchi Fan

doi:10.3390/cryst11060702

Abstract

Raw powders are processed in water during the freeze-dry pulsated orifice ejection method (FD-POEM), leading to the inclusion of oxygen impurities. This study proposes a strategy for removing the oxygen content and enhancing the mechanical performance of laser powder bed fusion (L-PBF) builds from powders using carbon nanotubes (CNTs) and H2 reduction. Spherical 1.5 wt.% CNT/Mo composite powders with uniform dispersion were fabricated via FD-POEM. The quantity of MoO2 decreased significantly, and a hexagonally structured Mo2C phase was simultaneously formed in the L-PBF build. The Mo2C with network structure was distributed along the boundaries of equiaxed Mo grains, leading to an increased Vickers hardness of the matrix. This study demonstrates the feasibility of fabricating oxygen-free and high-strength refractory parts during L-PBF for ultrahigh-temperature applications.

Highlights

Refractory metals have gained significant attention in the academic and industrial fields [1,2,3]
It is noteworthy that the dispersion state of the slurry is an important factor in obtaining a stable slurry for freeze-dry pulsated orifice ejection method (FD-POEM) because a heterogeneous deposition phenomenon does not occur during slurry fabrication
It was obvious that certain circumference-type nano defects were introduced on the outer layers of the carbon nanotubes (CNTs), as observed by transmission electron microscopy (TEM), indicating a defective character

Summary

Introduction

Refractory metals have gained significant attention in the academic and industrial fields [1,2,3]. Metals are melted, thereby impacting the inert gas jet, water pressure, or high-temperature plasma and atomizing into particles These methods exhibit certain limitations owing to the high melting points of the refractory materials. Carbon nanotubes (CNTs) were chosen as ideal reduction agents by adding them to Mo powders processed by FD-POEM to remove oxygen. The reason for this is twofold: first, acid-treated CNTs can exist individually because of their functionalized surfaces [32]. The feasibility of the in situ removal of oxygen from Mo built by the addition of CNTs into powders processed by FD-POEM during L-PBF was investigated. These builds were subjected to microstructural analysis and mechanical characterization

Characterizations

Results and Discussion

Conclusions