Key Takeaways & Executive Findings
- •• In-situ synchrotron X-ray imaging reveals three distinct bubble growth modes in LPBF of oxide ceramics: uplift growth, gas channel attachment, and bubble coalescence. • Bursting of large bubbles induces melt flow oscillations, leading to local instability of the melt pool and potential pore formation. • Understanding bubble dynamics provides critical insights for optimizing LPBF parameters to eliminate porosity and enhance mechanical properties of oxide ceramics. • The study directly links bubble behavior to melt pool instability, offering a pathway to reduce defects in additively manufactured ceramics.
Abstract
Laser powder bed fusion (LPBF) is used to fabricate complex-shaped, dense, and high-performance oxide ceramics. During LPBF, bubbles form and evolve in the melt pool and ultimately remain in the printed ceramics as pores, which significantly degrade the mechanical properties. Therefore, it is essential to understand the bubble behaviors during LPBF. Herein, we conducted an in-situ investigation of the bubble dynamics in the melt pool of homogeneously mixed Al2O3–Y2O3 powders using synchrotron high-speed X-ray imaging. The formation, growth, motion, and evolution of bubbles, as well as the relationship between the instability of melt flow and bubble rupture during LPBF, were elucidated. The findings reveal that bubbles from the interstices within the powder bed grow following three distinct modes, i.e., uplift growth, gas channel attachment, and bubble coalescence. Furthermore, melt flow oscillations caused by the bursting of large bubbles can lead to local instability of the melt pool. Results from this study enhance the understanding of bubble dynamics during LPBF and may provide valuable insights for pore elimination in LPBF-processed oxide ceramics.
1. Introduction
Oxide eutectic ceramics demonstrate high hardness, superior temperature resistance and intrinsic resistance to oxidative corrosion, and have been widely used as loaded components in extreme environments [1–2]. However, the inherent brittleness and low plastic deformability have constrained their use as complex structural components through traditional subtractive manufacturing, i.e., cutting, turning, or drilling [3]. Currently, indirect additive manufacturing (IAM), including stereo lithography appearance (SLA), digital light processing (DLP), and binder jetting (BJ), enables the fabrication of complex ceramic components through post-processing (debinding and sintering) [4–5]. Unfortunately, the required post-processing poses challenges in overcoming the limitations associated with the poor connecting, delamination and deformation of the ceramic components. Additionally, the volatilization of organic resins introduces porosity, which is typically more pronounced in parts with low density produced via IAM [6].
Compared to IAM, direct additive manufacturing (DAM) targets the fabrication and improves the production of high-density oxide ceramics with reduced porosity and enhanced properties, which can be achieved through laser powder bed fusion (LPBF) technology [7–8]. A high-density Al2O3 toughened ZrO2 part with high bending strength in the case of refined and homogenous microstructure has been successfully prepared by Verga et al. [9] via LPBF technology. Therefore, LPBF technology has been considered as an effective method to prepare high-performance oxide eutectic ceramics. The LPBF process of powders mainly includes powder spreading, laser melting and solidification. During laser melting, the interaction between laser and powder always promotes the formation of porosity, which is related to the combined effect of recoil pressure and melt flow, leading to the instability and collapse of the melt pool and the bubbles captured in the solidification front. Therefore, optimizing the process parameters of LPBF to eliminate the formation of porosity, and uncovering the relationship between melt pool and porosity elimination are of significance to improve the quality of components with high density.
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Zhun Su, Wenquan Lu, Zongye Ding, Liang Zhao, Fan Yang, Jianguo Li, Qiaodan Hu (2025). In-situ observation on bubble evolution during laser powder bed fusion of oxide ceramic. Int. Journal of Minerals, Metallurgy and Materials (矿物冶金与材料学报). https://doi.org/10.1007/s12613-025-3170-2
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Frequently Asked Questions
What are the three distinct bubble growth modes observed during LPBF of oxide ceramics?
The three distinct bubble growth modes are uplift growth, gas channel attachment, and bubble coalescence, as revealed by in-situ synchrotron X-ray imaging.
How does bubble bursting affect the melt pool during LPBF?
Bursting of large bubbles induces melt flow oscillations, which can lead to local instability of the melt pool, potentially affecting the final porosity and mechanical properties of the printed ceramic.
Why is it important to understand bubble dynamics in LPBF?
Understanding bubble dynamics is crucial for optimizing LPBF process parameters to eliminate porosity, thereby improving the density and mechanical performance of oxide ceramic components.
What technique was used for in-situ observation of bubble evolution?
The study utilized synchrotron high-speed X-ray imaging to observe bubble formation, growth, motion, and evolution in the melt pool during LPBF.
What material system was investigated in this study?
The study investigated homogeneously mixed Al2O3–Y2O3 powders, which are relevant for oxide eutectic ceramics.
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