Nanoparticle Tracing during Laser Powder Bed Fusion of Oxide Dispersion Strengthened Steels

Abstract

The control of nanoparticle agglomeration during the fabrication of oxide dispersion strengthened steels is a key factor in maximizing their mechanical and high temperature reinforcement properties. However, the characterization of the nanoparticle evolution during processing represents a challenge due to the lack of experimental methodologies that allow in situ evaluation during laser powder bed fusion (LPBF) of nanoparticle-additivated steel powders. To address this problem, a simulation scheme is proposed to trace the drift and the interactions of the nanoparticles in the melt pool by joint heat-melt-microstructure–coupled phase-field simulation with nanoparticle kinematics. Van der Waals attraction and electrostatic repulsion with screened-Coulomb potential are explicitly employed to model the interactions with assumptions made based on reported experimental evidence. Numerical simulations have been conducted for LPBF of oxide nanoparticle-additivated PM2000 powder considering various factors, including the nanoparticle composition and size distribution. The obtained results provide a statistical and graphical demonstration of the temporal and spatial variations of the traced nanoparticles, showing ∼55% of the nanoparticles within the generated grains, and a smaller fraction of ∼30% in the pores, ∼13% on the surface, and ∼2% on the grain boundaries. To prove the methodology and compare it with experimental observations, the simulations are performed for LPBF of a 0.005 wt % yttrium oxide nanoparticle-additivated PM2000 powder and the final degree of nanoparticle agglomeration and distribution are analyzed with respect to a series of geometric and material parameters.

Nanoparticle Additivation Effects on Laser Powder Bed Fusion of Metals and Polymers—A Theoretical Concept for an Inter-Laboratory Study Design All Along the Process Chain, Including Research Data Management

“…Porosity in as-built metal and polymer parts significantly impacts the density, mechanical, and functional properties [57][58][59][60]. The microstructural formations and porosity distributions of the as-built parts can be affected by the dissolution degree, lattice misfit degree, high-temperature chemical stability, wetting degree, interface reactions, and laser absorptivity of NPs during PBF-LB processing [36,[82][83][84][85][86]. Further, the parts' relative density and porosity content can affect as-built parts' mechanical and functional properties [2,3].…”

“…As illustrated in Figure 7, laser power or energy density variations can affect the melt pool's undissolved the NPs rearrangement in the melt pool. Marangoni convection significantly impacts NP rearrangement in the metal melt pool [63,86,87]. Depending on the laser power or energy density, surface tension gradients between melt and solid drive a fluid flow in the melt pool.…”

“…Increasing laser power or energy density will increase the Marangoni convection and melt pool depth during processing. In addition, there can be other factors in melt pool dynamics: evaporation in the melt pool, recoil pressure, and inverted Marangoni flow direction due to inhomogeneous melt pool chemistry [36,63,75,78,86,87].…”

Manufacturing oxide-dispersion-strengthened steels using the advanced directed energy deposition process of high-speed laser cladding

“…Additionally, advanced particle agglomeration enforces buoyancy-induced flotation effects of nanoparticles leading to slag formation on the clads' surface and therefore reduced dispersion strengthening. [50] However, a direct comparison between the powder-blown deposition techniques of DED and HSLC, and the powder bed manufacturing process of L-PBF is difficult because of the strongly differing beam diameters (DED and HSLC: 0.66 mm [25], L-PBF: 0.08 mm [27]) leading to formation of increased melt pool dimensions in DED and HSLC, altering the solidification conditions significantly. The direct comparison of DED and HSLC with identical beam diameters used proves the ability to increase cooling and solidification rates leading to improved dispersion of nanoparticles in the stainless steel matrix reflected by smaller oxide particles in HSLC (50-150 nm) compared to DED (100-200 nm) [25].…”

New Frontiers in Materials Design for Laser Additive Manufacturing

“…Oxide dispersion strengthening (ODS) is an evolving example of how material development benefits from AM by providing a method to produce these types of composites more economically or at all. These advances also benefit from sophisticated modeling, e.g., [ 2 ] propose a model to predict the nanoparticle’s exact location in solidified LAM material. Another promising approach to modify powders at the nano level is to systematically coat them to improve process behavior, like, e.g., investigated by [ 3 ] on maraging tool steel.…”