# Investigation of Ti65 Powder Spreading Behavior in Multi-Layer Laser Powder Bed Fusion
## 5 Conclusions  
In this work, a multi-layer PBF-LB/Ti65 powder was investigated by using a coupled DEM-CFD approach. The macro- and microscopic properties of the powder beds across successive layers and different sub-regions were analyzed under various spreading velocities. Furthermore, the mechanisms of powder bed densification and void formation induced by the presence of a printed region were elucidated. The key findings are summarized as follows:  
1. The powder bed quality improves with increasing layer number. The first two layers exhibit low packing density and high surface roughness due to limited powder availability and a strong boundary effect. From the third layer onward, the powder bed properties stabilize, indicating a diminishing influence from the initial layer constraints.
2. Properly reducing the spreading velocity enhances powder bed quality, as evidenced by increased packing density, improved surface uniformity, a higher coordination number, and a reduced coefficient of variation. This improvement is attributed to the longer time available for particle rearrangement and void filling at lower velocities.
3. The printed region influences not only the powder bed formed directly above it (Zone 2) but also indirectly alters the bed quality in front of (Zone 1) and behind (Zone 3) it. As a result, the height profile of the powder bed across the three zones shows a decreasing trend along the spreading direction.
4. Mechanism analysis reveals that the printed region induces a high-contact force zone at the interface between Zones 1 and 2 due to the obstruction, leading to the formation of a low-velocity area and enhanced local densification. In Zone 2, particle motion is constrained by printed geometry, promoting a relatively dense packing structure. Driven by the recoating blade, only a limited number of particles fall into the area  
Figure 17: (**a**) Average contact forces of particles in Zone A4; (**b,c**) motion behaviors of particles in low-velocity zone and around the voids, respectively.  
ahead of Zone 3, leading to the formation of a pit. Additionally, due to insufficient particle supply, a relatively loosely packed powder bed forms in Zone 3.  
Conceptualization, G.Y., M.L. and X.A.; Methodology, Z.L., J.W. and H.Z.; Software, Z.L., X.L. and H.Z.; Validation, J.N. and Q.M.; Formal analysis, Z.L., J.W., G.Y., M.L. and X.A.; Investigation, J.W. and J.N.; Resources, Z.L., G.Y., X.L., M.L., X.A. and J.N.; Data curation, J.W., X.L., M.L. and Q.M.; Writing--original draft, Z.L.; Writing--review & editing, J.W., G.Y., X.L., X.A., J.N., H.Z. and Q.M.; Visualization, H.Z.; Supervision, X.A.; Project administration, X.A.; Funding acquisition, X.A. All authors have read and agreed to the published version of the manuscript.  
This research received no external funding.  
Not applicable.  
The raw data supporting the conclusions of this article will be made available by the authors on request.  
The authors are grateful to the Liaoning Revitalization Talents Program (XLYC1805007) and Fundamental Research Funds for the Central Universities (N2425007) of China for the financial support of current work.  
Authors [PERSON], [PERSON] and [PERSON] were employed by the company Shenyang Aircraft Industry Group Co., Ltd. The remaining authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.