Phase-separation induced dislocation-network cellular structures in Ti-Zr-Nb-Mo-Ta high-entropy alloy processed by laser powder bed fusion

Han Chen; Daisuke Egusa; Zehao Li; Taisuke Sasaki; Ryosuke Ozasa; Takuya Ishimoto; Masayuki Okugawa; Yuichiro Koizumi; Takayoshi Nakano; Eiji Abe

doi:10.1016/j.addma.2025.104737

Article Phase-separation induced dislocation-network cellular structures in Ti-Zr-Nb-Mo-Ta high-entropy alloy processed by laser powder bed fusion

Han Chen ; Daisuke Egusa ; Zehao Li (National Institute for Materials Science) ; Taisuke Sasaki (National Institute for Materials Science) ; Ryosuke Ozasa ; Takuya Ishimoto ; Masayuki Okugawa ; Yuichiro Koizumi ; Takayoshi Nakano ; Eiji Abe

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Han Chen, Daisuke Egusa, Zehao Li, Taisuke Sasaki, Ryosuke Ozasa, Takuya Ishimoto, Masayuki Okugawa, Yuichiro Koizumi, Takayoshi Nakano, Eiji Abe. Phase-separation induced dislocation-network cellular structures in Ti-Zr-Nb-Mo-Ta high-entropy alloy processed by laser powder bed fusion. Additive Manufacturing. 2025, 102 (), 104737. https://doi.org/10.1016/j.addma.2025.104737

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Hierarchical structures, such as cellular structures, elemental segregations, and dislocation-network, are often proposed to enhance the mechanical properties of high-entropy alloys (HEAs) fabricated via additive manufacturing (AM). The formation of cellular structures is often attributed to elemental segregation during the solidification process or thermal strain resulting from the AM process. Here, we present a novel cellular structure where phase-separation and dislocation-network coupled in Ti-Zr-Nb-Mo-Ta HEA processed by laser powder bed fusion (L-PBF). Electron microscopy observations and X-ray diffraction (XRD) analyses show that this unique cellular structure consists of Zr-rich and Ta-rich body-center cubic (BCC) phases as the cell-wall and the cell-core, respectively, with their lattice constant difference of about 1 %. Moreover, a higher density of dislocations forming distinct networks is detected within this cellular structure, whose density reached 8 × 1014 m−2. Ma- chine learning analysis reveals that the dislocations preferentially occur on the Zr-rich BCC side, thus accom- modating the strains significant around the boundaries between the two BCC phases. With the aid of thermodynamic simulations, we propose a formation mechanism of the present cellular structure, which is governed by the elemental partitioning behavior of Zr and Ta during a solid-state phase separation under rapid cooling. Boundaries with this phase separation are introduced as semi-coherent interfaces with misfit disloca- tions, introducing a high-density dislocation in the present material. This novel cellular structure can signifi- cantly enhance the strength of AM HEAs, providing valuable insights for developing high-performance AM metals through the design of hierarchical microstructures.

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