Relationship between cross-sectional plane and corresponding morphology in an immiscible alloy powder with core-deviated structure

Abstract

Immiscible alloy powders with core/shell structure have recently garnered considerable interest due to their excellent industrial performance. However, a frequently observed yet often overlooked feature is the presence of core-deviated structure in various cross-sectional planes of the powder. To date, limited research has been conducted on this structure and its origin, leaving the formation mechanism unclear. Gaining a comprehensive understanding of this mechanism is crucial for advancements in powder materials research. In this study, we first analyzed the solidification microstructures of Fe-68 wt.%Sn alloy powders, followed by a numerical analysis of airflow and internal temperature fields within a powder during the free-falling process. Our findings revealed that the average airflow velocity on the windward side is faster than that on the leeward side, causing the highest temperature point within the powder to shift towards the leeward side over time. This phenomenon is fundamentally linked to the formation of the core-deviated structure. Furthermore, we explored the relationship between cross-sectional planes and potential microstructures, demonstrating that the final observed structures are strongly influenced by the position and orientation of the cross-sectional plane. Additionally, the core deviation distance was theoretically predicted and found to be consistent with experimental results in Fe-68 wt.%Sn powders. This research provides valuable insights into the actual solidification process of immiscible alloy powders and contributes to the development of specialized structural materials.